diff --git a/components/collator/src/provider.rs b/components/collator/src/provider.rs
index 5e658e331ee..d394bebba72 100644
--- a/components/collator/src/provider.rs
+++ b/components/collator/src/provider.rs
@@ -117,7 +117,8 @@ fn data_ce_to_primary(data_ce: u64, c: char) -> u32 {
 #[icu_provider::data_struct(marker(
     CollationDataV1Marker,
     "collator/data@1",
-    fallback_by = "collation",
+    // TODO(#3867): Use script fallback
+    fallback_by = "language",
 ))]
 #[derive(Debug, PartialEq, Clone)]
 #[cfg_attr(feature = "datagen", derive(serde::Serialize, databake::Bake), databake(path = icu_collator::provider))]
@@ -231,7 +232,7 @@ impl<'data> CollationDataV1<'data> {
 #[icu_provider::data_struct(marker(
     CollationDiacriticsV1Marker,
     "collator/dia@1",
-    fallback_by = "collation",
+    fallback_by = "language",
 ))]
 #[derive(Debug, PartialEq, Clone)]
 #[cfg_attr(feature = "datagen", derive(serde::Serialize, databake::Bake), databake(path = icu_collator::provider))]
@@ -273,7 +274,7 @@ pub struct CollationJamoV1<'data> {
 #[icu_provider::data_struct(marker(
     CollationReorderingV1Marker,
     "collator/reord@1",
-    fallback_by = "collation",
+    fallback_by = "language",
 ))]
 #[derive(Debug, PartialEq, Clone)]
 #[cfg_attr(feature = "datagen", derive(serde::Serialize, databake::Bake), databake(path = icu_collator::provider))]
@@ -361,7 +362,7 @@ impl<'data> CollationReorderingV1<'data> {
 #[icu_provider::data_struct(marker(
     CollationMetadataV1Marker,
     "collator/meta@1",
-    fallback_by = "collation",
+    fallback_by = "language",
 ))]
 #[derive(Debug, PartialEq, Clone, Copy)]
 #[cfg_attr(feature = "datagen", derive(serde::Serialize, databake::Bake), databake(path = icu_collator::provider))]
diff --git a/components/experimental/src/personnames/formatter.rs b/components/experimental/src/personnames/formatter.rs
index b14edf8e366..2899d153f31 100644
--- a/components/experimental/src/personnames/formatter.rs
+++ b/components/experimental/src/personnames/formatter.rs
@@ -47,9 +47,7 @@ impl PersonNamesFormatter {
             + DataProvider<icu_properties::provider::ScriptWithExtensionsPropertyV1Marker>
             + DataProvider<icu_properties::provider::ScriptValueToShortNameV1Marker>
             + DataProvider<icu_locale::provider::LocaleFallbackLikelySubtagsV1Marker>
-            + DataProvider<icu_locale::provider::LocaleFallbackParentsV1Marker>
-            // TODO: We shouldn't need the collation supplement here
-            + DataProvider<icu_locale::provider::CollationFallbackSupplementV1Marker>,
+            + DataProvider<icu_locale::provider::LocaleFallbackParentsV1Marker>,
     {
         let swe = icu_properties::script::load_script_with_extensions_unstable(provider)?;
         let scripts = icu_properties::Script::get_enum_to_short_name_mapper(provider)?;
diff --git a/components/experimental/tests/personnames/tests.rs b/components/experimental/tests/personnames/tests.rs
index fb9b75ec707..446b742fd28 100644
--- a/components/experimental/tests/personnames/tests.rs
+++ b/components/experimental/tests/personnames/tests.rs
@@ -26,7 +26,6 @@ const _: () = {
     impl_person_names_format_v1_marker!(TestingProvider);
     icu_locale_data::impl_locale_fallback_likely_subtags_v1_marker!(TestingProvider);
     icu_locale_data::impl_locale_fallback_parents_v1_marker!(TestingProvider);
-    icu_locale_data::impl_collation_fallback_supplement_v1_marker!(TestingProvider);
     icu_properties_data::impl_script_value_to_short_name_v1_marker!(TestingProvider);
     icu_properties_data::impl_script_with_extensions_property_v1_marker!(TestingProvider);
 };
diff --git a/components/locale/src/fallback/algorithms.rs b/components/locale/src/fallback/algorithms.rs
index 7b5e76e9612..ee923e54c5d 100644
--- a/components/locale/src/fallback/algorithms.rs
+++ b/components/locale/src/fallback/algorithms.rs
@@ -63,16 +63,7 @@ impl<'a> LocaleFallbackerWithConfig<'a> {
             }
         }
         // 3. Remove irrelevant extension subtags
-        locale.retain_unicode_ext(|key| {
-            match *key {
-                // Always retain -u-sd
-                SUBDIVISION_KEY => true,
-                // Retain the query-specific keyword
-                _ if Some(*key) == self.config.extension_key => true,
-                // Drop all others
-                _ => false,
-            }
-        });
+        locale.retain_unicode_ext(|&key| matches!(key, SUBDIVISION_KEY));
         // 4. If there is an invalid "sd" subtag, drop it
         // For now, ignore it, and let fallback do it for us
     }
@@ -83,9 +74,6 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
         match self.config.priority {
             LocaleFallbackPriority::Language => self.step_language(locale),
             LocaleFallbackPriority::Region => self.step_region(locale),
-            // TODO(#1964): Change the collation fallback rules to be different
-            // from the language fallback fules.
-            LocaleFallbackPriority::Collation => self.step_language(locale),
             // This case should not normally happen, but `LocaleFallbackPriority` is non_exhaustive.
             // Make it go directly to `und`.
             _ => {
@@ -100,13 +88,6 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
     }
 
     fn step_language(&mut self, locale: &mut DataLocale) {
-        // 1. Remove the extension fallback keyword
-        if let Some(extension_key) = self.config.extension_key {
-            if let Some(value) = locale.remove_unicode_ext(&extension_key) {
-                self.backup_extension = Some(value);
-                return;
-            }
-        }
         // 2. Remove the subdivision keyword
         if let Some(value) = locale.remove_unicode_ext(&SUBDIVISION_KEY) {
             self.backup_subdivision = Some(value);
@@ -122,7 +103,7 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
         // 5. Check for parent override
         if let Some(parent) = self.get_explicit_parent(locale) {
             locale.set_langid(parent);
-            self.restore_extensions_variants(locale);
+            self.restore_subdivision_variants(locale);
             return;
         }
         // 6. Add the script subtag if necessary
@@ -134,7 +115,7 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
                     &region.into_tinystr().to_unvalidated(),
                 ) {
                     locale.set_script(Some(script));
-                    self.restore_extensions_variants(locale);
+                    self.restore_subdivision_variants(locale);
                     return;
                 }
             }
@@ -142,7 +123,7 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
         // 7. Remove region
         if locale.region().is_some() {
             locale.set_region(None);
-            self.restore_extensions_variants(locale);
+            self.restore_subdivision_variants(locale);
             return;
         }
         // 8. Remove language+script
@@ -152,13 +133,6 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
     }
 
     fn step_region(&mut self, locale: &mut DataLocale) {
-        // 1. Remove the extension fallback keyword
-        if let Some(extension_key) = self.config.extension_key {
-            if let Some(value) = locale.remove_unicode_ext(&extension_key) {
-                self.backup_extension = Some(value);
-                return;
-            }
-        }
         // 2. Remove the subdivision keyword
         if let Some(value) = locale.remove_unicode_ext(&SUBDIVISION_KEY) {
             self.backup_subdivision = Some(value);
@@ -175,7 +149,7 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
         if !locale.language().is_empty() || locale.script().is_some() {
             locale.set_script(None);
             locale.set_language(Language::UND);
-            self.restore_extensions_variants(locale);
+            self.restore_subdivision_variants(locale);
             return;
         }
         // 6. Remove region
@@ -183,11 +157,7 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
         locale.set_region(None);
     }
 
-    fn restore_extensions_variants(&mut self, locale: &mut DataLocale) {
-        if let Some(value) = self.backup_extension.take() {
-            #[allow(clippy::unwrap_used)] // not reachable unless extension_key is present
-            locale.set_unicode_ext(self.config.extension_key.unwrap(), value);
-        }
+    fn restore_subdivision_variants(&mut self, locale: &mut DataLocale) {
         if let Some(value) = self.backup_subdivision.take() {
             locale.set_unicode_ext(SUBDIVISION_KEY, value);
         }
@@ -197,17 +167,9 @@ impl<'a> LocaleFallbackIteratorInner<'a> {
     }
 
     fn get_explicit_parent(&self, locale: &DataLocale) -> Option<LanguageIdentifier> {
-        self.supplement
-            .and_then(|supplement| {
-                supplement
-                    .parents
-                    .get_copied_by(|uvstr| locale.strict_cmp(uvstr).reverse())
-            })
-            .or_else(|| {
-                self.parents
-                    .parents
-                    .get_copied_by(|uvstr| locale.strict_cmp(uvstr).reverse())
-            })
+        self.parents
+            .parents
+            .get_copied_by(|uvstr| locale.strict_cmp(uvstr).reverse())
             .map(LanguageIdentifier::from)
     }
 }
@@ -220,8 +182,6 @@ mod tests {
     struct TestCase {
         input: &'static str,
         requires_data: bool,
-        extension_key: Option<Key>,
-        fallback_supplement: Option<LocaleFallbackSupplement>,
         // Note: The first entry in the chain is the normalized locale
         expected_language_chain: &'static [&'static str],
         expected_region_chain: &'static [&'static str],
@@ -232,40 +192,30 @@ mod tests {
         TestCase {
             input: "en-u-hc-h12-sd-usca",
             requires_data: false,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en-u-sd-usca", "en"],
             expected_region_chain: &["en-u-sd-usca", "en", "und-u-sd-usca"],
         },
         TestCase {
             input: "en-US-u-hc-h12-sd-usca",
             requires_data: false,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en-US-u-sd-usca", "en-US", "en-u-sd-usca", "en"],
             expected_region_chain: &["en-US-u-sd-usca", "en-US", "und-US-u-sd-usca", "und-US"],
         },
         TestCase {
             input: "en-US-fonipa-u-hc-h12-sd-usca",
             requires_data: false,
-            extension_key: Some(key!("hc")),
-            fallback_supplement: None,
             expected_language_chain: &[
-                "en-US-fonipa-u-hc-h12-sd-usca",
                 "en-US-fonipa-u-sd-usca",
                 "en-US-fonipa",
                 "en-US",
-                "en-fonipa-u-hc-h12-sd-usca",
                 "en-fonipa-u-sd-usca",
                 "en-fonipa",
                 "en",
             ],
             expected_region_chain: &[
-                "en-US-fonipa-u-hc-h12-sd-usca",
                 "en-US-fonipa-u-sd-usca",
                 "en-US-fonipa",
                 "en-US",
-                "und-US-fonipa-u-hc-h12-sd-usca",
                 "und-US-fonipa-u-sd-usca",
                 "und-US-fonipa",
                 "und-US",
@@ -274,24 +224,18 @@ mod tests {
         TestCase {
             input: "en-u-hc-h12-sd-usca",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en-u-sd-usca", "en"],
             expected_region_chain: &["en-US-u-sd-usca", "en-US", "und-US-u-sd-usca", "und-US"],
         },
         TestCase {
             input: "en-Latn-u-sd-usca",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en-u-sd-usca", "en"],
             expected_region_chain: &["en-US-u-sd-usca", "en-US", "und-US-u-sd-usca", "und-US"],
         },
         TestCase {
             input: "en-Latn-US-u-sd-usca",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en-US-u-sd-usca", "en-US", "en-u-sd-usca", "en"],
             expected_region_chain: &["en-US-u-sd-usca", "en-US", "und-US-u-sd-usca", "und-US"],
         },
@@ -299,32 +243,24 @@ mod tests {
             // TODO(#4413): -u-rg is not yet supported; when it is, this test should be updated
             input: "en-u-rg-gbxxxx",
             requires_data: false,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["en"],
             expected_region_chain: &["en"],
         },
         TestCase {
             input: "sr-ME",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["sr-ME", "sr-Latn-ME", "sr-Latn"],
             expected_region_chain: &["sr-ME", "und-ME"],
         },
         TestCase {
             input: "sr-Latn-ME",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["sr-ME", "sr-Latn-ME", "sr-Latn"],
             expected_region_chain: &["sr-ME", "und-ME"],
         },
         TestCase {
             input: "sr-ME-fonipa",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &[
                 "sr-ME-fonipa",
                 "sr-ME",
@@ -338,72 +274,54 @@ mod tests {
         TestCase {
             input: "sr-RS",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["sr-RS", "sr"],
             expected_region_chain: &["sr-RS", "und-RS"],
         },
         TestCase {
             input: "sr-Cyrl-RS",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["sr-RS", "sr"],
             expected_region_chain: &["sr-RS", "und-RS"],
         },
         TestCase {
             input: "sr-Latn-RS",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["sr-Latn-RS", "sr-Latn"],
             expected_region_chain: &["sr-Latn-RS", "und-RS"],
         },
         TestCase {
             input: "de-Latn-LI",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["de-LI", "de"],
             expected_region_chain: &["de-LI", "und-LI"],
         },
         TestCase {
             input: "ca-ES-valencia",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["ca-ES-valencia", "ca-ES", "ca-valencia", "ca"],
             expected_region_chain: &["ca-ES-valencia", "ca-ES", "und-ES-valencia", "und-ES"],
         },
         TestCase {
             input: "es-AR",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["es-AR", "es-419", "es"],
             expected_region_chain: &["es-AR", "und-AR"],
         },
         TestCase {
             input: "hi-IN",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["hi-IN", "hi"],
             expected_region_chain: &["hi-IN", "und-IN"],
         },
         TestCase {
             input: "hi-Latn-IN",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["hi-Latn-IN", "hi-Latn", "en-IN", "en-001", "en"],
             expected_region_chain: &["hi-Latn-IN", "und-IN"],
         },
         TestCase {
             input: "zh-CN",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             // Note: "zh-Hans" is not reachable because it is the default script for "zh".
             // The fallback algorithm does not visit the language-script bundle when the
             // script is the default for the language
@@ -413,26 +331,21 @@ mod tests {
         TestCase {
             input: "zh-TW",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["zh-TW", "zh-Hant-TW", "zh-Hant"],
             expected_region_chain: &["zh-TW", "und-TW"],
         },
         TestCase {
             input: "yue-HK",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: None,
             expected_language_chain: &["yue-HK", "yue"],
             expected_region_chain: &["yue-HK", "und-HK"],
         },
         TestCase {
             input: "yue-HK",
             requires_data: true,
-            extension_key: None,
-            fallback_supplement: Some(LocaleFallbackSupplement::Collation),
-            expected_language_chain: &["yue-HK", "yue", "zh-Hant", "zh"],
+            expected_language_chain: &["yue-HK", "yue"],
             expected_region_chain: &["yue-HK", "und-HK"],
+            // TODO(#3867): script fallback should do zh-Hant or und-Hant as well
         },
     ];
 
@@ -451,8 +364,6 @@ mod tests {
             ] {
                 let mut config = LocaleFallbackConfig::default();
                 config.priority = priority;
-                config.extension_key = cas.extension_key;
-                config.fallback_supplement = cas.fallback_supplement;
                 let fallbacker = if cas.requires_data {
                     fallbacker_with_data
                 } else {
diff --git a/components/locale/src/fallback/mod.rs b/components/locale/src/fallback/mod.rs
index 5954af8b19c..69f4b852eb4 100644
--- a/components/locale/src/fallback/mod.rs
+++ b/components/locale/src/fallback/mod.rs
@@ -11,9 +11,7 @@ use icu_locale_core::subtags::Variants;
 use icu_provider::prelude::*;
 
 #[doc(inline)]
-pub use icu_provider::_internal::{
-    LocaleFallbackConfig, LocaleFallbackPriority, LocaleFallbackSupplement,
-};
+pub use icu_provider::_internal::{LocaleFallbackConfig, LocaleFallbackPriority};
 
 mod algorithms;
 
@@ -35,7 +33,7 @@ mod algorithms;
 /// let fallbacker = LocaleFallbacker::new();
 ///
 /// // Create a LocaleFallbackerIterator with a default configuration.
-/// // By default, uses language priority with no additional extension keywords.
+/// // By default, uses language priority.
 /// let mut fallback_iterator = fallbacker
 ///     .for_config(Default::default())
 ///     .fallback_for(locale!("hi-Latn-IN").into());
@@ -62,7 +60,6 @@ mod algorithms;
 pub struct LocaleFallbacker {
     likely_subtags: DataPayload<LocaleFallbackLikelySubtagsV1Marker>,
     parents: DataPayload<LocaleFallbackParentsV1Marker>,
-    collation_supplement: Option<DataPayload<CollationFallbackSupplementV1Marker>>,
 }
 
 /// Borrowed version of [`LocaleFallbacker`].
@@ -70,7 +67,6 @@ pub struct LocaleFallbacker {
 pub struct LocaleFallbackerBorrowed<'a> {
     likely_subtags: &'a LocaleFallbackLikelySubtagsV1<'a>,
     parents: &'a LocaleFallbackParentsV1<'a>,
-    collation_supplement: Option<&'a LocaleFallbackSupplementV1<'a>>,
 }
 
 /// A [`LocaleFallbackerBorrowed`] with an associated [`LocaleFallbackConfig`].
@@ -78,7 +74,6 @@ pub struct LocaleFallbackerBorrowed<'a> {
 pub struct LocaleFallbackerWithConfig<'a> {
     likely_subtags: &'a LocaleFallbackLikelySubtagsV1<'a>,
     parents: &'a LocaleFallbackParentsV1<'a>,
-    supplement: Option<&'a LocaleFallbackSupplementV1<'a>>,
     config: LocaleFallbackConfig,
 }
 
@@ -87,9 +82,7 @@ pub struct LocaleFallbackerWithConfig<'a> {
 struct LocaleFallbackIteratorInner<'a> {
     likely_subtags: &'a LocaleFallbackLikelySubtagsV1<'a>,
     parents: &'a LocaleFallbackParentsV1<'a>,
-    supplement: Option<&'a LocaleFallbackSupplementV1<'a>>,
     config: LocaleFallbackConfig,
-    backup_extension: Option<Value>,
     backup_subdivision: Option<Value>,
     backup_variants: Option<Variants>,
 }
@@ -118,9 +111,6 @@ impl LocaleFallbacker {
             likely_subtags:
                 crate::provider::Baked::SINGLETON_LOCALE_FALLBACK_LIKELY_SUBTAGS_V1_MARKER,
             parents: crate::provider::Baked::SINGLETON_LOCALE_FALLBACK_PARENTS_V1_MARKER,
-            collation_supplement: Some(
-                crate::provider::Baked::SINGLETON_COLLATION_FALLBACK_SUPPLEMENT_V1_MARKER,
-            ),
         };
         // Safety: we're transmuting down from LocaleFallbackerBorrowed<'static> to LocaleFallbackerBorrowed<'a>
         // ZeroMaps use associated types in a way that confuse the compiler which gives up and marks them
@@ -144,27 +134,13 @@ impl LocaleFallbacker {
     where
         P: DataProvider<LocaleFallbackLikelySubtagsV1Marker>
             + DataProvider<LocaleFallbackParentsV1Marker>
-            + DataProvider<CollationFallbackSupplementV1Marker>
             + ?Sized,
     {
         let likely_subtags = provider.load(Default::default())?.payload;
         let parents = provider.load(Default::default())?.payload;
-        let collation_supplement = match DataProvider::<CollationFallbackSupplementV1Marker>::load(
-            provider,
-            Default::default(),
-        ) {
-            Ok(response) => Some(response.payload),
-            // It is expected that not all keys are present
-            Err(DataError {
-                kind: DataErrorKind::MarkerNotFound,
-                ..
-            }) => None,
-            Err(e) => return Err(e),
-        };
         Ok(LocaleFallbacker {
             likely_subtags,
             parents,
-            collation_supplement,
         })
     }
 
@@ -174,7 +150,6 @@ impl LocaleFallbacker {
         LocaleFallbacker {
             likely_subtags: DataPayload::from_owned(Default::default()),
             parents: DataPayload::from_owned(Default::default()),
-            collation_supplement: None,
         }
     }
 
@@ -189,7 +164,6 @@ impl LocaleFallbacker {
         LocaleFallbackerBorrowed {
             likely_subtags: self.likely_subtags.get(),
             parents: self.parents.get(),
-            collation_supplement: self.collation_supplement.as_ref().map(|p| p.get()),
         }
     }
 }
@@ -201,10 +175,6 @@ impl<'a> LocaleFallbackerBorrowed<'a> {
         LocaleFallbackerWithConfig {
             likely_subtags: self.likely_subtags,
             parents: self.parents,
-            supplement: match config.fallback_supplement {
-                Some(LocaleFallbackSupplement::Collation) => self.collation_supplement,
-                _ => None,
-            },
             config,
         }
     }
@@ -219,10 +189,6 @@ impl LocaleFallbackerBorrowed<'static> {
         LocaleFallbacker {
             likely_subtags: DataPayload::from_static_ref(self.likely_subtags),
             parents: DataPayload::from_static_ref(self.parents),
-            collation_supplement: match self.collation_supplement {
-                None => None,
-                Some(x) => Some(DataPayload::from_static_ref(x)),
-            },
         }
     }
 }
@@ -240,9 +206,7 @@ impl<'a> LocaleFallbackerWithConfig<'a> {
             inner: LocaleFallbackIteratorInner {
                 likely_subtags: self.likely_subtags,
                 parents: self.parents,
-                supplement: self.supplement,
                 config: self.config,
-                backup_extension: None,
                 backup_subdivision: None,
                 backup_variants: None,
             },
diff --git a/components/locale/src/provider/fallback.rs b/components/locale/src/provider/fallback.rs
index dcd5f7bbf73..4fc50473779 100644
--- a/components/locale/src/provider/fallback.rs
+++ b/components/locale/src/provider/fallback.rs
@@ -3,7 +3,6 @@
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
 use super::*;
-use icu_locale_core::extensions::unicode::Key;
 use icu_locale_core::subtags::{region, script, Language, Region, Script};
 use icu_provider::prelude::*;
 use zerovec::ule::UnvalidatedStr;
@@ -77,26 +76,3 @@ pub struct LocaleFallbackParentsV1<'data> {
     #[cfg_attr(feature = "serde", serde(borrow))]
     pub parents: ZeroMap<'data, UnvalidatedStr, (Language, Option<Script>, Option<Region>)>,
 }
-
-/// Key-specific supplemental fallback data.
-#[icu_provider::data_struct(marker(
-    CollationFallbackSupplementV1Marker,
-    "fallback/supplement/co@1",
-    singleton,
-))]
-#[derive(Default, Clone, PartialEq, Debug)]
-#[cfg_attr(
-    feature = "datagen",
-    derive(serde::Serialize, databake::Bake),
-    databake(path = icu_locale::provider),
-)]
-#[cfg_attr(feature = "serde", derive(serde::Deserialize))]
-#[yoke(prove_covariance_manually)]
-pub struct LocaleFallbackSupplementV1<'data> {
-    /// Additional parent locales to supplement the common ones.
-    #[cfg_attr(feature = "serde", serde(borrow))]
-    pub parents: ZeroMap<'data, UnvalidatedStr, (Language, Option<Script>, Option<Region>)>,
-    /// Default values for Unicode extension keywords.
-    #[cfg_attr(feature = "serde", serde(borrow))]
-    pub unicode_extension_defaults: ZeroMap2d<'data, Key, UnvalidatedStr, UnvalidatedStr>,
-}
diff --git a/components/locale/src/provider/mod.rs b/components/locale/src/provider/mod.rs
index 624e4e3ed9d..9b07a27da6e 100644
--- a/components/locale/src/provider/mod.rs
+++ b/components/locale/src/provider/mod.rs
@@ -46,7 +46,6 @@ const _: () = {
     make_provider!(Baked);
     impl_locale_fallback_likely_subtags_v1_marker!(Baked);
     impl_locale_fallback_parents_v1_marker!(Baked);
-    impl_collation_fallback_supplement_v1_marker!(Baked);
     impl_aliases_v2_marker!(Baked);
     impl_likely_subtags_extended_v1_marker!(Baked);
     impl_likely_subtags_for_language_v1_marker!(Baked);
@@ -61,7 +60,6 @@ use icu_provider::prelude::*;
 /// The latest minimum set of markers required by this component.
 pub const MARKERS: &[DataMarkerInfo] = &[
     AliasesV2Marker::INFO,
-    CollationFallbackSupplementV1Marker::INFO,
     LikelySubtagsExtendedV1Marker::INFO,
     LikelySubtagsForLanguageV1Marker::INFO,
     LikelySubtagsForScriptRegionV1Marker::INFO,
diff --git a/documents/process/writing_a_new_data_struct.md b/documents/process/writing_a_new_data_struct.md
index 95346dbcf78..6a19b793f55 100644
--- a/documents/process/writing_a_new_data_struct.md
+++ b/documents/process/writing_a_new_data_struct.md
@@ -95,7 +95,7 @@ use icu_provider::prelude::*;
 use icu::decimal::provider::{ AffixesV1, GroupingSizesV1 };
 
 /// Symbols and metadata required for formatting a [`FixedDecimal`](crate::FixedDecimal).
-#[icu_provider::data_struct(marker(DecimalSymbolsV1Marker, "decimal/symbols@1", extension_key = "nu" ))]
+#[icu_provider::data_struct(DecimalSymbolsV1Marker = "decimal/symbols@1")]
 #[derive(Debug, PartialEq, Clone)]
 #[cfg_attr(
     feature = "datagen",
diff --git a/ffi/capi/bindings/c/LocaleFallbackConfig.d.h b/ffi/capi/bindings/c/LocaleFallbackConfig.d.h
index ee0b2f6825e..b72b6a5ae76 100644
--- a/ffi/capi/bindings/c/LocaleFallbackConfig.d.h
+++ b/ffi/capi/bindings/c/LocaleFallbackConfig.d.h
@@ -8,15 +8,12 @@
 #include "diplomat_runtime.h"
 
 #include "LocaleFallbackPriority.d.h"
-#include "LocaleFallbackSupplement.d.h"
 
 
 
 
 typedef struct LocaleFallbackConfig {
   LocaleFallbackPriority priority;
-  DiplomatStringView extension_key;
-  LocaleFallbackSupplement fallback_supplement;
 } LocaleFallbackConfig;
 
 
diff --git a/ffi/capi/bindings/c/LocaleFallbackPriority.d.h b/ffi/capi/bindings/c/LocaleFallbackPriority.d.h
index 683c8f38c31..a8ecf599a28 100644
--- a/ffi/capi/bindings/c/LocaleFallbackPriority.d.h
+++ b/ffi/capi/bindings/c/LocaleFallbackPriority.d.h
@@ -14,7 +14,6 @@
 typedef enum LocaleFallbackPriority {
   LocaleFallbackPriority_Language = 0,
   LocaleFallbackPriority_Region = 1,
-  LocaleFallbackPriority_Collation = 2,
 } LocaleFallbackPriority;
 
 
diff --git a/ffi/capi/bindings/c/LocaleFallbackSupplement.d.h b/ffi/capi/bindings/c/LocaleFallbackSupplement.d.h
deleted file mode 100644
index 8c712796f2a..00000000000
--- a/ffi/capi/bindings/c/LocaleFallbackSupplement.d.h
+++ /dev/null
@@ -1,23 +0,0 @@
-#ifndef LocaleFallbackSupplement_D_H
-#define LocaleFallbackSupplement_D_H
-
-#include <stdio.h>
-#include <stdint.h>
-#include <stddef.h>
-#include <stdbool.h>
-#include "diplomat_runtime.h"
-
-
-
-
-
-typedef enum LocaleFallbackSupplement {
-  LocaleFallbackSupplement_None = 0,
-  LocaleFallbackSupplement_Collation = 1,
-} LocaleFallbackSupplement;
-
-
-
-
-
-#endif // LocaleFallbackSupplement_D_H
diff --git a/ffi/capi/bindings/c/LocaleFallbackSupplement.h b/ffi/capi/bindings/c/LocaleFallbackSupplement.h
deleted file mode 100644
index 2a5cd4a223e..00000000000
--- a/ffi/capi/bindings/c/LocaleFallbackSupplement.h
+++ /dev/null
@@ -1,23 +0,0 @@
-#ifndef LocaleFallbackSupplement_H
-#define LocaleFallbackSupplement_H
-
-#include <stdio.h>
-#include <stdint.h>
-#include <stddef.h>
-#include <stdbool.h>
-#include "diplomat_runtime.h"
-
-
-#include "LocaleFallbackSupplement.d.h"
-
-
-
-
-
-
-
-
-
-
-
-#endif // LocaleFallbackSupplement_H
diff --git a/ffi/capi/bindings/c/LocaleFallbacker.h b/ffi/capi/bindings/c/LocaleFallbacker.h
index aca807736ca..7241aa54e1d 100644
--- a/ffi/capi/bindings/c/LocaleFallbacker.h
+++ b/ffi/capi/bindings/c/LocaleFallbacker.h
@@ -11,7 +11,6 @@
 #include "DataProvider.d.h"
 #include "LocaleFallbackConfig.d.h"
 #include "LocaleFallbackerWithConfig.d.h"
-#include "LocaleParseError.d.h"
 
 #include "LocaleFallbacker.d.h"
 
@@ -25,8 +24,7 @@ icu4x_LocaleFallbacker_create_mv1_result icu4x_LocaleFallbacker_create_mv1(const
 
 LocaleFallbacker* icu4x_LocaleFallbacker_without_data_mv1(void);
 
-typedef struct icu4x_LocaleFallbacker_for_config_mv1_result {union {LocaleFallbackerWithConfig* ok; LocaleParseError err;}; bool is_ok;} icu4x_LocaleFallbacker_for_config_mv1_result;
-icu4x_LocaleFallbacker_for_config_mv1_result icu4x_LocaleFallbacker_for_config_mv1(const LocaleFallbacker* self, LocaleFallbackConfig config);
+LocaleFallbackerWithConfig* icu4x_LocaleFallbacker_for_config_mv1(const LocaleFallbacker* self, LocaleFallbackConfig config);
 
 
 void icu4x_LocaleFallbacker_destroy_mv1(LocaleFallbacker* self);
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.d.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.d.hpp
index 0c79dfcd6bf..9cb0dc86f4f 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.d.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.d.hpp
@@ -9,11 +9,9 @@
 #include <optional>
 #include "../diplomat_runtime.hpp"
 #include "LocaleFallbackPriority.d.hpp"
-#include "LocaleFallbackSupplement.d.hpp"
 
 namespace icu4x {
 class LocaleFallbackPriority;
-class LocaleFallbackSupplement;
 }
 
 
@@ -21,8 +19,6 @@ namespace icu4x {
 namespace capi {
     struct LocaleFallbackConfig {
       icu4x::capi::LocaleFallbackPriority priority;
-      diplomat::capi::DiplomatStringView extension_key;
-      icu4x::capi::LocaleFallbackSupplement fallback_supplement;
     };
 } // namespace capi
 } // namespace
@@ -31,8 +27,6 @@ namespace capi {
 namespace icu4x {
 struct LocaleFallbackConfig {
   icu4x::LocaleFallbackPriority priority;
-  std::string_view extension_key;
-  icu4x::LocaleFallbackSupplement fallback_supplement;
 
   inline icu4x::capi::LocaleFallbackConfig AsFFI() const;
   inline static icu4x::LocaleFallbackConfig FromFFI(icu4x::capi::LocaleFallbackConfig c_struct);
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.hpp
index 102981eed34..e808a34f06a 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackConfig.hpp
@@ -11,7 +11,6 @@
 #include <optional>
 #include "../diplomat_runtime.hpp"
 #include "LocaleFallbackPriority.hpp"
-#include "LocaleFallbackSupplement.hpp"
 
 
 namespace icu4x {
@@ -27,16 +26,12 @@ namespace capi {
 inline icu4x::capi::LocaleFallbackConfig icu4x::LocaleFallbackConfig::AsFFI() const {
   return icu4x::capi::LocaleFallbackConfig {
     /* .priority = */ priority.AsFFI(),
-    /* .extension_key = */ {extension_key.data(), extension_key.size()},
-    /* .fallback_supplement = */ fallback_supplement.AsFFI(),
   };
 }
 
 inline icu4x::LocaleFallbackConfig icu4x::LocaleFallbackConfig::FromFFI(icu4x::capi::LocaleFallbackConfig c_struct) {
   return icu4x::LocaleFallbackConfig {
     /* .priority = */ icu4x::LocaleFallbackPriority::FromFFI(c_struct.priority),
-    /* .extension_key = */ std::string_view(c_struct.extension_key.data, c_struct.extension_key.len),
-    /* .fallback_supplement = */ icu4x::LocaleFallbackSupplement::FromFFI(c_struct.fallback_supplement),
   };
 }
 
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.d.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.d.hpp
index 5b137ffa74d..8f1b1e9476b 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.d.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.d.hpp
@@ -15,7 +15,6 @@ namespace capi {
     enum LocaleFallbackPriority {
       LocaleFallbackPriority_Language = 0,
       LocaleFallbackPriority_Region = 1,
-      LocaleFallbackPriority_Collation = 2,
     };
 } // namespace capi
 } // namespace
@@ -26,7 +25,6 @@ class LocaleFallbackPriority {
   enum Value {
     Language = 0,
     Region = 1,
-    Collation = 2,
   };
 
   LocaleFallbackPriority() = default;
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.hpp
index 6b9a5608154..cff568e6d85 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackPriority.hpp
@@ -29,7 +29,6 @@ inline icu4x::LocaleFallbackPriority icu4x::LocaleFallbackPriority::FromFFI(icu4
   switch (c_enum) {
     case icu4x::capi::LocaleFallbackPriority_Language:
     case icu4x::capi::LocaleFallbackPriority_Region:
-    case icu4x::capi::LocaleFallbackPriority_Collation:
       return static_cast<icu4x::LocaleFallbackPriority::Value>(c_enum);
     default:
       abort();
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.d.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.d.hpp
deleted file mode 100644
index 51245b1316d..00000000000
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.d.hpp
+++ /dev/null
@@ -1,44 +0,0 @@
-#ifndef icu4x_LocaleFallbackSupplement_D_HPP
-#define icu4x_LocaleFallbackSupplement_D_HPP
-
-#include <stdio.h>
-#include <stdint.h>
-#include <stddef.h>
-#include <stdbool.h>
-#include <memory>
-#include <optional>
-#include "../diplomat_runtime.hpp"
-
-
-namespace icu4x {
-namespace capi {
-    enum LocaleFallbackSupplement {
-      LocaleFallbackSupplement_None = 0,
-      LocaleFallbackSupplement_Collation = 1,
-    };
-} // namespace capi
-} // namespace
-
-namespace icu4x {
-class LocaleFallbackSupplement {
-public:
-  enum Value {
-    None = 0,
-    Collation = 1,
-  };
-
-  LocaleFallbackSupplement() = default;
-  // Implicit conversions between enum and ::Value
-  constexpr LocaleFallbackSupplement(Value v) : value(v) {}
-  constexpr operator Value() const { return value; }
-  // Prevent usage as boolean value
-  explicit operator bool() const = delete;
-
-  inline icu4x::capi::LocaleFallbackSupplement AsFFI() const;
-  inline static icu4x::LocaleFallbackSupplement FromFFI(icu4x::capi::LocaleFallbackSupplement c_enum);
-private:
-    Value value;
-};
-
-} // namespace
-#endif // icu4x_LocaleFallbackSupplement_D_HPP
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.hpp
deleted file mode 100644
index 356da64a8be..00000000000
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbackSupplement.hpp
+++ /dev/null
@@ -1,37 +0,0 @@
-#ifndef icu4x_LocaleFallbackSupplement_HPP
-#define icu4x_LocaleFallbackSupplement_HPP
-
-#include "LocaleFallbackSupplement.d.hpp"
-
-#include <stdio.h>
-#include <stdint.h>
-#include <stddef.h>
-#include <stdbool.h>
-#include <memory>
-#include <optional>
-#include "../diplomat_runtime.hpp"
-
-
-namespace icu4x {
-namespace capi {
-    extern "C" {
-    
-    
-    } // extern "C"
-} // namespace capi
-} // namespace
-
-inline icu4x::capi::LocaleFallbackSupplement icu4x::LocaleFallbackSupplement::AsFFI() const {
-  return static_cast<icu4x::capi::LocaleFallbackSupplement>(value);
-}
-
-inline icu4x::LocaleFallbackSupplement icu4x::LocaleFallbackSupplement::FromFFI(icu4x::capi::LocaleFallbackSupplement c_enum) {
-  switch (c_enum) {
-    case icu4x::capi::LocaleFallbackSupplement_None:
-    case icu4x::capi::LocaleFallbackSupplement_Collation:
-      return static_cast<icu4x::LocaleFallbackSupplement::Value>(c_enum);
-    default:
-      abort();
-  }
-}
-#endif // icu4x_LocaleFallbackSupplement_HPP
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.d.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.d.hpp
index 42928fafff7..c864bc757ad 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.d.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.d.hpp
@@ -18,7 +18,6 @@ namespace capi { struct LocaleFallbackerWithConfig; }
 class LocaleFallbackerWithConfig;
 struct LocaleFallbackConfig;
 class DataError;
-class LocaleParseError;
 }
 
 
@@ -36,7 +35,7 @@ class LocaleFallbacker {
 
   inline static std::unique_ptr<icu4x::LocaleFallbacker> without_data();
 
-  inline diplomat::result<std::unique_ptr<icu4x::LocaleFallbackerWithConfig>, icu4x::LocaleParseError> for_config(icu4x::LocaleFallbackConfig config) const;
+  inline std::unique_ptr<icu4x::LocaleFallbackerWithConfig> for_config(icu4x::LocaleFallbackConfig config) const;
 
   inline const icu4x::capi::LocaleFallbacker* AsFFI() const;
   inline icu4x::capi::LocaleFallbacker* AsFFI();
diff --git a/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.hpp b/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.hpp
index 287c1697e43..ae45af5357a 100644
--- a/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.hpp
+++ b/ffi/capi/bindings/cpp/icu4x/LocaleFallbacker.hpp
@@ -14,7 +14,6 @@
 #include "DataProvider.hpp"
 #include "LocaleFallbackConfig.hpp"
 #include "LocaleFallbackerWithConfig.hpp"
-#include "LocaleParseError.hpp"
 
 
 namespace icu4x {
@@ -26,8 +25,7 @@ namespace capi {
     
     icu4x::capi::LocaleFallbacker* icu4x_LocaleFallbacker_without_data_mv1(void);
     
-    typedef struct icu4x_LocaleFallbacker_for_config_mv1_result {union {icu4x::capi::LocaleFallbackerWithConfig* ok; icu4x::capi::LocaleParseError err;}; bool is_ok;} icu4x_LocaleFallbacker_for_config_mv1_result;
-    icu4x_LocaleFallbacker_for_config_mv1_result icu4x_LocaleFallbacker_for_config_mv1(const icu4x::capi::LocaleFallbacker* self, icu4x::capi::LocaleFallbackConfig config);
+    icu4x::capi::LocaleFallbackerWithConfig* icu4x_LocaleFallbacker_for_config_mv1(const icu4x::capi::LocaleFallbacker* self, icu4x::capi::LocaleFallbackConfig config);
     
     
     void icu4x_LocaleFallbacker_destroy_mv1(LocaleFallbacker* self);
@@ -46,10 +44,10 @@ inline std::unique_ptr<icu4x::LocaleFallbacker> icu4x::LocaleFallbacker::without
   return std::unique_ptr<icu4x::LocaleFallbacker>(icu4x::LocaleFallbacker::FromFFI(result));
 }
 
-inline diplomat::result<std::unique_ptr<icu4x::LocaleFallbackerWithConfig>, icu4x::LocaleParseError> icu4x::LocaleFallbacker::for_config(icu4x::LocaleFallbackConfig config) const {
+inline std::unique_ptr<icu4x::LocaleFallbackerWithConfig> icu4x::LocaleFallbacker::for_config(icu4x::LocaleFallbackConfig config) const {
   auto result = icu4x::capi::icu4x_LocaleFallbacker_for_config_mv1(this->AsFFI(),
     config.AsFFI());
-  return result.is_ok ? diplomat::result<std::unique_ptr<icu4x::LocaleFallbackerWithConfig>, icu4x::LocaleParseError>(diplomat::Ok<std::unique_ptr<icu4x::LocaleFallbackerWithConfig>>(std::unique_ptr<icu4x::LocaleFallbackerWithConfig>(icu4x::LocaleFallbackerWithConfig::FromFFI(result.ok)))) : diplomat::result<std::unique_ptr<icu4x::LocaleFallbackerWithConfig>, icu4x::LocaleParseError>(diplomat::Err<icu4x::LocaleParseError>(icu4x::LocaleParseError::FromFFI(result.err)));
+  return std::unique_ptr<icu4x::LocaleFallbackerWithConfig>(icu4x::LocaleFallbackerWithConfig::FromFFI(result));
 }
 
 inline const icu4x::capi::LocaleFallbacker* icu4x::LocaleFallbacker::AsFFI() const {
diff --git a/ffi/capi/bindings/dart/LocaleFallbackConfig.g.dart b/ffi/capi/bindings/dart/LocaleFallbackConfig.g.dart
index 8082b122518..aa2023fd961 100644
--- a/ffi/capi/bindings/dart/LocaleFallbackConfig.g.dart
+++ b/ffi/capi/bindings/dart/LocaleFallbackConfig.g.dart
@@ -5,9 +5,6 @@ part of 'lib.g.dart';
 final class _LocaleFallbackConfigFfi extends ffi.Struct {
   @ffi.Int32()
   external int priority;
-  external _SliceUtf8 extensionKey;
-  @ffi.Int32()
-  external int fallbackSupplement;
 }
 
 /// Collection of configurations for the ICU4X fallback algorithm.
@@ -15,51 +12,32 @@ final class _LocaleFallbackConfigFfi extends ffi.Struct {
 /// See the [Rust documentation for `LocaleFallbackConfig`](https://docs.rs/icu/latest/icu/locale/fallback/struct.LocaleFallbackConfig.html) for more information.
 final class LocaleFallbackConfig {
   LocaleFallbackPriority priority;
-  String extensionKey;
-  LocaleFallbackSupplement fallbackSupplement;
 
-  LocaleFallbackConfig({required this.priority, required this.extensionKey, required this.fallbackSupplement});
+  LocaleFallbackConfig({required this.priority});
 
+  // This struct contains borrowed fields, so this takes in a list of
+  // "edges" corresponding to where each lifetime's data may have been borrowed from
+  // and passes it down to individual fields containing the borrow.
+  // This method does not attempt to handle any dependencies between lifetimes, the caller
+  // should handle this when constructing edge arrays.
   // ignore: unused_element
-  LocaleFallbackConfig._fromFfi(_LocaleFallbackConfigFfi ffi, core.List<Object> aEdges) :
-    priority = LocaleFallbackPriority.values[ffi.priority],
-    extensionKey = ffi.extensionKey._toDart(aEdges),
-    fallbackSupplement = LocaleFallbackSupplement.values[ffi.fallbackSupplement];
+  LocaleFallbackConfig._fromFfi(_LocaleFallbackConfigFfi ffi) :
+    priority = LocaleFallbackPriority.values[ffi.priority];
 
-  // If this struct contains any slices, their lifetime-edge-relevant objects (typically _FinalizedArenas) will only
-  // be constructed here, and can be appended to any relevant lifetime arrays here. <lifetime>AppendArray accepts a list
-  // of arrays for each lifetime to do so. It accepts multiple lists per lifetime in case the caller needs to tie a lifetime to multiple
-  // output arrays. Null is equivalent to an empty list: this lifetime is not being borrowed from.
   // ignore: unused_element
-  _LocaleFallbackConfigFfi _toFfi(ffi.Allocator temp, {core.List<core.List<Object>> aAppendArray = const []}) {
+  _LocaleFallbackConfigFfi _toFfi(ffi.Allocator temp) {
     final struct = ffi.Struct.create<_LocaleFallbackConfigFfi>();
     struct.priority = priority.index;
-    final extensionKeyView = extensionKey.utf8View;
-    struct.extensionKey._length = extensionKeyView.length;
-    struct.extensionKey._data = extensionKeyView.allocIn(aAppendArray.isNotEmpty ? _FinalizedArena.withLifetime(aAppendArray).arena : temp);
-    struct.fallbackSupplement = fallbackSupplement.index;
     return struct;
   }
 
   @override
   bool operator ==(Object other) =>
       other is LocaleFallbackConfig &&
-      other.priority == priority &&
-      other.extensionKey == extensionKey &&
-      other.fallbackSupplement == fallbackSupplement;
+      other.priority == priority;
 
   @override
   int get hashCode => Object.hashAll([
         priority,
-        extensionKey,
-        fallbackSupplement,
       ]);
-
-  // Return all fields corresponding to lifetime `'a` 
-  // without handling lifetime dependencies (this is the job of the caller)
-  // This is all fields that may be borrowed from if borrowing `'a`,
-  // assuming that there are no `'other: a`. bounds. In case of such bounds,
-  // the caller should take care to also call _fieldsForLifetimeOther
-  // ignore: unused_element
-  core.List<Object> get _fieldsForLifetimeA => [extensionKey];
 }
diff --git a/ffi/capi/bindings/dart/LocaleFallbackPriority.g.dart b/ffi/capi/bindings/dart/LocaleFallbackPriority.g.dart
index 5f6d7958c97..6d8eef26060 100644
--- a/ffi/capi/bindings/dart/LocaleFallbackPriority.g.dart
+++ b/ffi/capi/bindings/dart/LocaleFallbackPriority.g.dart
@@ -8,7 +8,5 @@ part of 'lib.g.dart';
 enum LocaleFallbackPriority {
   language,
 
-  region,
-
-  collation;
+  region;
 }
diff --git a/ffi/capi/bindings/dart/LocaleFallbackSupplement.g.dart b/ffi/capi/bindings/dart/LocaleFallbackSupplement.g.dart
deleted file mode 100644
index a6775817329..00000000000
--- a/ffi/capi/bindings/dart/LocaleFallbackSupplement.g.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// generated by diplomat-tool
-
-part of 'lib.g.dart';
-
-/// What additional data is required to load when performing fallback.
-///
-/// See the [Rust documentation for `LocaleFallbackSupplement`](https://docs.rs/icu/latest/icu/locale/fallback/enum.LocaleFallbackSupplement.html) for more information.
-enum LocaleFallbackSupplement {
-  none,
-
-  collation;
-}
diff --git a/ffi/capi/bindings/dart/LocaleFallbacker.g.dart b/ffi/capi/bindings/dart/LocaleFallbacker.g.dart
index d95903ca8f7..a8ca1f46698 100644
--- a/ffi/capi/bindings/dart/LocaleFallbacker.g.dart
+++ b/ffi/capi/bindings/dart/LocaleFallbacker.g.dart
@@ -48,18 +48,13 @@ final class LocaleFallbacker implements ffi.Finalizable {
   /// Associates this `LocaleFallbacker` with configuration options.
   ///
   /// See the [Rust documentation for `for_config`](https://docs.rs/icu/latest/icu/locale/fallback/struct.LocaleFallbacker.html#method.for_config) for more information.
-  ///
-  /// Throws [LocaleParseError] on failure.
   LocaleFallbackerWithConfig forConfig(LocaleFallbackConfig config) {
     final temp = ffi2.Arena();
     // This lifetime edge depends on lifetimes: 'a
     core.List<Object> aEdges = [this];
     final result = _icu4x_LocaleFallbacker_for_config_mv1(_ffi, config._toFfi(temp));
     temp.releaseAll();
-    if (!result.isOk) {
-      throw LocaleParseError.values[result.union.err];
-    }
-    return LocaleFallbackerWithConfig._fromFfi(result.union.ok, [], aEdges);
+    return LocaleFallbackerWithConfig._fromFfi(result, [], aEdges);
   }
 }
 
@@ -79,6 +74,6 @@ external _ResultOpaqueInt32 _icu4x_LocaleFallbacker_create_mv1(ffi.Pointer<ffi.O
 external ffi.Pointer<ffi.Opaque> _icu4x_LocaleFallbacker_without_data_mv1();
 
 @meta.ResourceIdentifier('icu4x_LocaleFallbacker_for_config_mv1')
-@ffi.Native<_ResultOpaqueInt32 Function(ffi.Pointer<ffi.Opaque>, _LocaleFallbackConfigFfi)>(isLeaf: true, symbol: 'icu4x_LocaleFallbacker_for_config_mv1')
+@ffi.Native<ffi.Pointer<ffi.Opaque> Function(ffi.Pointer<ffi.Opaque>, _LocaleFallbackConfigFfi)>(isLeaf: true, symbol: 'icu4x_LocaleFallbacker_for_config_mv1')
 // ignore: non_constant_identifier_names
-external _ResultOpaqueInt32 _icu4x_LocaleFallbacker_for_config_mv1(ffi.Pointer<ffi.Opaque> self, _LocaleFallbackConfigFfi config);
+external ffi.Pointer<ffi.Opaque> _icu4x_LocaleFallbacker_for_config_mv1(ffi.Pointer<ffi.Opaque> self, _LocaleFallbackConfigFfi config);
diff --git a/ffi/capi/bindings/dart/lib.g.dart b/ffi/capi/bindings/dart/lib.g.dart
index d829dc4b490..08f2f86d4a0 100644
--- a/ffi/capi/bindings/dart/lib.g.dart
+++ b/ffi/capi/bindings/dart/lib.g.dart
@@ -96,7 +96,6 @@ part 'LocaleExpander.g.dart';
 part 'LocaleFallbackConfig.g.dart';
 part 'LocaleFallbackIterator.g.dart';
 part 'LocaleFallbackPriority.g.dart';
-part 'LocaleFallbackSupplement.g.dart';
 part 'LocaleFallbacker.g.dart';
 part 'LocaleFallbackerWithConfig.g.dart';
 part 'LocaleParseError.g.dart';
diff --git a/ffi/capi/bindings/js/LocaleFallbackConfig.d.ts b/ffi/capi/bindings/js/LocaleFallbackConfig.d.ts
index 5963823c57e..56dd3586cc8 100644
--- a/ffi/capi/bindings/js/LocaleFallbackConfig.d.ts
+++ b/ffi/capi/bindings/js/LocaleFallbackConfig.d.ts
@@ -1,6 +1,5 @@
 // generated by diplomat-tool
 import type { LocaleFallbackPriority } from "./LocaleFallbackPriority"
-import type { LocaleFallbackSupplement } from "./LocaleFallbackSupplement"
 import type { pointer, char } from "./diplomat-runtime.d.ts";
 
 
@@ -11,10 +10,6 @@ import type { pointer, char } from "./diplomat-runtime.d.ts";
 export class LocaleFallbackConfig {
     get priority() : LocaleFallbackPriority;
     set priority(value: LocaleFallbackPriority); 
-    get extensionKey() : string;
-    set extensionKey(value: string); 
-    get fallbackSupplement() : LocaleFallbackSupplement;
-    set fallbackSupplement(value: LocaleFallbackSupplement); 
 
     
 
diff --git a/ffi/capi/bindings/js/LocaleFallbackConfig.mjs b/ffi/capi/bindings/js/LocaleFallbackConfig.mjs
index 015b060ec8f..8b7e48d77e5 100644
--- a/ffi/capi/bindings/js/LocaleFallbackConfig.mjs
+++ b/ffi/capi/bindings/js/LocaleFallbackConfig.mjs
@@ -1,6 +1,5 @@
 // generated by diplomat-tool
 import { LocaleFallbackPriority } from "./LocaleFallbackPriority.mjs"
-import { LocaleFallbackSupplement } from "./LocaleFallbackSupplement.mjs"
 import wasm from "./diplomat-wasm.mjs";
 import * as diplomatRuntime from "./diplomat-runtime.mjs";
 
@@ -17,55 +16,28 @@ export class LocaleFallbackConfig {
     set priority(value) {
         this.#priority = value;
     }
-    #extensionKey;
-    get extensionKey()  {
-        return this.#extensionKey;
-    }
-    set extensionKey(value) {
-        this.#extensionKey = value;
-    }
-    #fallbackSupplement;
-    get fallbackSupplement()  {
-        return this.#fallbackSupplement;
-    }
-    set fallbackSupplement(value) {
-        this.#fallbackSupplement = value;
-    }
 
     // Return this struct in FFI function friendly format.
     // Returns an array that can be expanded with spread syntax (...)
-    // If this struct contains any slices, their lifetime-edge-relevant information will be
-    // set up here, and can be appended to any relevant lifetime arrays here. <lifetime>AppendArray accepts a list
-    // of arrays for each lifetime to do so. It accepts multiple lists per lifetime in case the caller needs to tie a lifetime to multiple
-    // output arrays. Null is equivalent to an empty list: this lifetime is not being borrowed from.
+    
     _intoFFI(
         slice_cleanup_callbacks,
         appendArrayMap
     ) {
-        slice_cleanup_callbacks.push((appendArrayMap[aAppendArray] || []).length > 0 ? () => { for (let lifetime of appendArrayMap[aAppendArray]) { appendArrayMap[aAppendArray].push(extensionKey); } extensionKey.garbageCollect(); } : extensionKey.free);
-        
-        return [this.#priority.ffiValue, diplomatRuntime.DiplomatBuf.str8(wasm, this.#extensionKey), this.#fallbackSupplement.ffiValue]
+        return [this.#priority.ffiValue]
     }
 
-    _fromFFI(ptr, aEdges) {
+    // This struct contains borrowed fields, so this takes in a list of
+    // "edges" corresponding to where each lifetime's data may have been borrowed from
+    // and passes it down to individual fields containing the borrow.
+    // This method does not attempt to handle any dependencies between lifetimes, the caller
+    // should handle this when constructing edge arrays.
+    _fromFFI(ptr) {
         const priorityDeref = diplomatRuntime.enumDiscriminant(wasm, ptr);
         this.#priority = LocaleFallbackPriority[Array.from(LocaleFallbackPriority.values.keys())[priorityDeref]];
-        const extensionKeyDeref = ptr + 4;
-        this.#extensionKey = diplomatRuntime.DiplomatBuf.stringFromPtr(wasm.memory.buffer, extensionKeyDeref, "string8");
-        const fallbackSupplementDeref = diplomatRuntime.enumDiscriminant(wasm, ptr + 12);
-        this.#fallbackSupplement = LocaleFallbackSupplement[Array.from(LocaleFallbackSupplement.values.keys())[fallbackSupplementDeref]];
 
         return this;
     }
-
-    // Return all fields corresponding to lifetime `'a` 
-    // without handling lifetime dependencies (this is the job of the caller)
-    // This is all fields that may be borrowed from if borrowing `'a`,
-    // assuming that there are no `'other: a`. bounds. In case of such bounds,
-    // the caller should take care to also call _fieldsForLifetimeOther
-    get _fieldsForLifetimeA() { 
-        return [extensionKey];
-    };
     
 
 }
\ No newline at end of file
diff --git a/ffi/capi/bindings/js/LocaleFallbackPriority.d.ts b/ffi/capi/bindings/js/LocaleFallbackPriority.d.ts
index 6e42fd725e7..857950e9a2e 100644
--- a/ffi/capi/bindings/js/LocaleFallbackPriority.d.ts
+++ b/ffi/capi/bindings/js/LocaleFallbackPriority.d.ts
@@ -17,8 +17,6 @@ export class LocaleFallbackPriority {
 
     static Region : LocaleFallbackPriority;
 
-    static Collation : LocaleFallbackPriority;
-
 
     
 
diff --git a/ffi/capi/bindings/js/LocaleFallbackPriority.mjs b/ffi/capi/bindings/js/LocaleFallbackPriority.mjs
index c880dff1b63..0a9e18f2483 100644
--- a/ffi/capi/bindings/js/LocaleFallbackPriority.mjs
+++ b/ffi/capi/bindings/js/LocaleFallbackPriority.mjs
@@ -12,8 +12,7 @@ export class LocaleFallbackPriority {
 
     static values = new Map([
         ["Language", 0],
-        ["Region", 1],
-        ["Collation", 2]
+        ["Region", 1]
     ]);
     constructor(value) {
         if (value instanceof LocaleFallbackPriority) {
@@ -41,8 +40,6 @@ export class LocaleFallbackPriority {
 
     static Region = new LocaleFallbackPriority("Region");
 
-    static Collation = new LocaleFallbackPriority("Collation");
-
 
     
 
diff --git a/ffi/capi/bindings/js/LocaleFallbackSupplement.d.ts b/ffi/capi/bindings/js/LocaleFallbackSupplement.d.ts
deleted file mode 100644
index 8c7138dffb8..00000000000
--- a/ffi/capi/bindings/js/LocaleFallbackSupplement.d.ts
+++ /dev/null
@@ -1,23 +0,0 @@
-// generated by diplomat-tool
-import type { pointer, char } from "./diplomat-runtime.d.ts";
-
-// Base enumerator definition
-/** What additional data is required to load when performing fallback.
-*
-*See the [Rust documentation for `LocaleFallbackSupplement`](https://docs.rs/icu/latest/icu/locale/fallback/enum.LocaleFallbackSupplement.html) for more information.
-*/
-export class LocaleFallbackSupplement {
-    constructor(value : LocaleFallbackSupplement | string);
-
-    get value() : string;
-
-    get ffiValue() : number;
-
-    static None : LocaleFallbackSupplement;
-
-    static Collation : LocaleFallbackSupplement;
-
-
-    
-
-}
\ No newline at end of file
diff --git a/ffi/capi/bindings/js/LocaleFallbackSupplement.mjs b/ffi/capi/bindings/js/LocaleFallbackSupplement.mjs
deleted file mode 100644
index da09b7676ac..00000000000
--- a/ffi/capi/bindings/js/LocaleFallbackSupplement.mjs
+++ /dev/null
@@ -1,46 +0,0 @@
-// generated by diplomat-tool
-import wasm from "./diplomat-wasm.mjs";
-import * as diplomatRuntime from "./diplomat-runtime.mjs";
-
-// Base enumerator definition
-/** What additional data is required to load when performing fallback.
-*
-*See the [Rust documentation for `LocaleFallbackSupplement`](https://docs.rs/icu/latest/icu/locale/fallback/enum.LocaleFallbackSupplement.html) for more information.
-*/
-export class LocaleFallbackSupplement {
-    #value = undefined;
-
-    static values = new Map([
-        ["None", 0],
-        ["Collation", 1]
-    ]);
-    constructor(value) {
-        if (value instanceof LocaleFallbackSupplement) {
-            this.#value = value.value;
-            return;
-        }
-
-        if (LocaleFallbackSupplement.values.has(value)) {
-            this.#value = value;
-            return;
-        }
-
-        throw TypeError(value + " is not a LocaleFallbackSupplement and does not correspond to any of its enumerator values.");
-    }
-
-    get value() {
-        return this.#value;
-    }
-
-    get ffiValue() {
-        return LocaleFallbackSupplement.values.get(this.#value);
-    }
-
-    static None = new LocaleFallbackSupplement("None");
-
-    static Collation = new LocaleFallbackSupplement("Collation");
-
-
-    
-
-}
\ No newline at end of file
diff --git a/ffi/capi/bindings/js/LocaleFallbacker.mjs b/ffi/capi/bindings/js/LocaleFallbacker.mjs
index c67b8c5c3b7..0bc732d4aec 100644
--- a/ffi/capi/bindings/js/LocaleFallbacker.mjs
+++ b/ffi/capi/bindings/js/LocaleFallbacker.mjs
@@ -3,7 +3,6 @@ import { DataError } from "./DataError.mjs"
 import { DataProvider } from "./DataProvider.mjs"
 import { LocaleFallbackConfig } from "./LocaleFallbackConfig.mjs"
 import { LocaleFallbackerWithConfig } from "./LocaleFallbackerWithConfig.mjs"
-import { LocaleParseError } from "./LocaleParseError.mjs"
 import wasm from "./diplomat-wasm.mjs";
 import * as diplomatRuntime from "./diplomat-runtime.mjs";
 
@@ -72,27 +71,19 @@ export class LocaleFallbacker {
         
         let slice_cleanup_callbacks = [];
         
-        const diplomat_receive_buffer = wasm.diplomat_alloc(5, 4);
-        
         // This lifetime edge depends on lifetimes 'a
         let aEdges = [this];
-        const result = wasm.icu4x_LocaleFallbacker_for_config_mv1(diplomat_receive_buffer, this.ffiValue, ...config._intoFFI(slice_cleanup_callbacks, {}));
+        const result = wasm.icu4x_LocaleFallbacker_for_config_mv1(this.ffiValue, ...config._intoFFI(slice_cleanup_callbacks, {}));
     
         try {
     
-            if (!diplomatRuntime.resultFlag(wasm, diplomat_receive_buffer, 4)) {
-                const cause = LocaleParseError[Array.from(LocaleParseError.values.keys())[diplomatRuntime.enumDiscriminant(wasm, diplomat_receive_buffer)]];
-                throw new Error('LocaleParseError: ' + cause.value, { cause });
-            }
-            return new LocaleFallbackerWithConfig(diplomatRuntime.ptrRead(wasm, diplomat_receive_buffer), [], aEdges);
+            return new LocaleFallbackerWithConfig(result, [], aEdges);
         } finally {
         
             for (let cleanup of slice_cleanup_callbacks) {
                 cleanup();
             }
         
-            wasm.diplomat_free(diplomat_receive_buffer, 5, 4);
-        
         }
     }
 
diff --git a/ffi/capi/bindings/js/index.d.ts b/ffi/capi/bindings/js/index.d.ts
index 7b6fc010bfb..2899e10d739 100644
--- a/ffi/capi/bindings/js/index.d.ts
+++ b/ffi/capi/bindings/js/index.d.ts
@@ -240,8 +240,6 @@ export { LocaleParseError } from "./LocaleParseError"
 
 export { LocaleFallbackPriority } from "./LocaleFallbackPriority"
 
-export { LocaleFallbackSupplement } from "./LocaleFallbackSupplement"
-
 export { FixedDecimalRoundingIncrement } from "./FixedDecimalRoundingIncrement"
 
 export { FixedDecimalRoundingMode } from "./FixedDecimalRoundingMode"
diff --git a/ffi/capi/bindings/js/index.mjs b/ffi/capi/bindings/js/index.mjs
index b7db3336a7d..d84f52b7955 100644
--- a/ffi/capi/bindings/js/index.mjs
+++ b/ffi/capi/bindings/js/index.mjs
@@ -238,8 +238,6 @@ export { LocaleParseError } from "./LocaleParseError.mjs"
 
 export { LocaleFallbackPriority } from "./LocaleFallbackPriority.mjs"
 
-export { LocaleFallbackSupplement } from "./LocaleFallbackSupplement.mjs"
-
 export { FixedDecimalRoundingIncrement } from "./FixedDecimalRoundingIncrement.mjs"
 
 export { FixedDecimalRoundingMode } from "./FixedDecimalRoundingMode.mjs"
diff --git a/ffi/capi/src/fallbacker.rs b/ffi/capi/src/fallbacker.rs
index 98ab497718d..ce9f5ca258c 100644
--- a/ffi/capi/src/fallbacker.rs
+++ b/ffi/capi/src/fallbacker.rs
@@ -8,7 +8,6 @@
 pub mod ffi {
     use alloc::boxed::Box;
 
-    use crate::errors::ffi::LocaleParseError;
     use crate::{errors::ffi::DataError, locale_core::ffi::Locale, provider::ffi::DataProvider};
 
     /// An object that runs the ICU4X locale fallback algorithm.
@@ -28,19 +27,6 @@ pub mod ffi {
     pub enum LocaleFallbackPriority {
         Language = 0,
         Region = 1,
-        Collation = 2,
-    }
-
-    /// What additional data is required to load when performing fallback.
-    #[diplomat::rust_link(icu::locale::fallback::LocaleFallbackSupplement, Enum)]
-    #[diplomat::rust_link(
-        icu::locale::fallback::LocaleFallbackSupplement::const_default,
-        FnInEnum,
-        hidden
-    )]
-    pub enum LocaleFallbackSupplement {
-        None = 0,
-        Collation = 1,
     }
 
     /// Collection of configurations for the ICU4X fallback algorithm.
@@ -50,13 +36,9 @@ pub mod ffi {
         FnInStruct,
         hidden
     )]
-    pub struct LocaleFallbackConfig<'a> {
+    pub struct LocaleFallbackConfig {
         /// Choice of priority mode.
         pub priority: LocaleFallbackPriority,
-        /// An empty string is considered `None`.
-        pub extension_key: &'a DiplomatStr,
-        /// Fallback supplement data key to customize fallback rules.
-        pub fallback_supplement: LocaleFallbackSupplement,
     }
 
     /// An object that runs the ICU4X locale fallback algorithm with specific configurations.
@@ -104,13 +86,15 @@ pub mod ffi {
             FnInStruct,
             hidden
         )]
-        pub fn for_config<'a, 'temp>(
+        pub fn for_config<'a>(
             &'a self,
-            config: LocaleFallbackConfig<'temp>,
-        ) -> Result<Box<LocaleFallbackerWithConfig<'a>>, LocaleParseError> {
-            Ok(Box::new(LocaleFallbackerWithConfig(self.0.for_config(
-                icu_locale::fallback::LocaleFallbackConfig::try_from(config)?,
-            ))))
+            config: LocaleFallbackConfig,
+        ) -> Box<LocaleFallbackerWithConfig<'a>> {
+            Box::new(LocaleFallbackerWithConfig(self.0.for_config({
+                let mut c = icu_locale::fallback::LocaleFallbackConfig::default();
+                c.priority = config.priority.into();
+                c
+            })))
         }
     }
 
@@ -166,22 +150,3 @@ pub mod ffi {
         }
     }
 }
-
-impl TryFrom<ffi::LocaleFallbackConfig<'_>> for icu_locale::fallback::LocaleFallbackConfig {
-    type Error = crate::errors::ffi::LocaleParseError;
-    fn try_from(other: ffi::LocaleFallbackConfig) -> Result<Self, Self::Error> {
-        let mut result = Self::default();
-        result.priority = other.priority.into();
-        result.extension_key = match other.extension_key {
-            b"" => None,
-            s => Some(icu_locale_core::extensions::unicode::Key::try_from_utf8(s)?),
-        };
-        result.fallback_supplement = match other.fallback_supplement {
-            ffi::LocaleFallbackSupplement::None => None,
-            ffi::LocaleFallbackSupplement::Collation => {
-                Some(icu_locale::fallback::LocaleFallbackSupplement::Collation)
-            }
-        };
-        Ok(result)
-    }
-}
diff --git a/ffi/dart/test/icu_test.dart b/ffi/dart/test/icu_test.dart
index ed6bd63c150..bd90474a1e8 100644
--- a/ffi/dart/test/icu_test.dart
+++ b/ffi/dart/test/icu_test.dart
@@ -11,18 +11,11 @@ void main() {
 
   test('LocaleFallbacker', () {
     final iterator = LocaleFallbacker(DataProvider.compiled())
-        .forConfig(LocaleFallbackConfig(
-            extensionKey: 'ca',
-            priority: LocaleFallbackPriority.region,
-            fallbackSupplement: LocaleFallbackSupplement.none))
+        .forConfig(LocaleFallbackConfig(priority: LocaleFallbackPriority.region))
         .fallbackForLocale(Locale.fromString('de-CH-u-ca-japanese'));
     expect(iterator.moveNext(), true);
-    expect(iterator.current, Locale.fromString('de-CH-u-ca-japanese'));
-    expect(iterator.moveNext(), true);
     expect(iterator.current, Locale.fromString('de-CH'));
     expect(iterator.moveNext(), true);
-    expect(iterator.current, Locale.fromString('und-CH-u-ca-japanese'));
-    expect(iterator.moveNext(), true);
     expect(iterator.current, Locale.fromString('und-CH'));
     expect(iterator.moveNext(), false);
   });
diff --git a/provider/core/macros/src/lib.rs b/provider/core/macros/src/lib.rs
index 263271f132c..c81f3b63b8d 100644
--- a/provider/core/macros/src/lib.rs
+++ b/provider/core/macros/src/lib.rs
@@ -62,7 +62,6 @@ mod tests;
 /// #     pub use icu_provider::_internal::locale_core::*;
 /// #   }
 /// # }
-/// use icu::locale::extensions::unicode::key;
 /// use icu::locale::fallback::*;
 /// use icu_provider::prelude::*;
 /// use std::borrow::Cow;
@@ -74,7 +73,6 @@ mod tests;
 ///         BazV1Marker,
 ///         "demo/baz@1",
 ///         fallback_by = "region",
-///         extension_key = "ca"
 ///     )
 /// )]
 /// pub struct FooV1<'data> {
@@ -89,14 +87,12 @@ mod tests;
 ///     BarV1Marker::INFO.fallback_config.priority,
 ///     LocaleFallbackPriority::Language
 /// );
-/// assert_eq!(BarV1Marker::INFO.fallback_config.extension_key, None);
 ///
 /// assert_eq!(BazV1Marker::INFO.path.as_str(), "demo/baz@1");
 /// assert_eq!(
 ///     BazV1Marker::INFO.fallback_config.priority,
 ///     LocaleFallbackPriority::Region
 /// );
-/// assert_eq!(BazV1Marker::INFO.fallback_config.extension_key, Some(key!("ca")));
 /// ```
 pub fn data_struct(attr: TokenStream, item: TokenStream) -> TokenStream {
     TokenStream::from(data_struct_impl(
@@ -119,8 +115,6 @@ struct DataStructArg {
     marker_name: Path,
     path_lit: Option<LitStr>,
     fallback_by: Option<LitStr>,
-    extension_key: Option<LitStr>,
-    fallback_supplement: Option<LitStr>,
     singleton: bool,
 }
 
@@ -130,8 +124,6 @@ impl DataStructArg {
             marker_name,
             path_lit: None,
             fallback_by: None,
-            extension_key: None,
-            fallback_supplement: None,
             singleton: false,
         }
     }
@@ -163,8 +155,6 @@ impl Parse for DataStructArg {
             let mut marker_name: Option<Path> = None;
             let mut path_lit: Option<LitStr> = None;
             let mut fallback_by: Option<LitStr> = None;
-            let mut extension_key: Option<LitStr> = None;
-            let mut fallback_supplement: Option<LitStr> = None;
             let mut singleton = false;
             let punct = content.parse_terminated(DataStructMarkerArg::parse, Token![,])?;
 
@@ -181,20 +171,6 @@ impl Parse for DataStructArg {
                                 "fallback_by",
                                 paren.span.join(),
                             )?;
-                        } else if name == "extension_key" {
-                            at_most_one_option(
-                                &mut extension_key,
-                                value,
-                                "extension_key",
-                                paren.span.join(),
-                            )?;
-                        } else if name == "fallback_supplement" {
-                            at_most_one_option(
-                                &mut fallback_supplement,
-                                value,
-                                "fallback_supplement",
-                                paren.span.join(),
-                            )?;
                         } else {
                             return Err(parse::Error::new(
                                 name.span(),
@@ -223,8 +199,6 @@ impl Parse for DataStructArg {
                 marker_name,
                 path_lit,
                 fallback_by,
-                extension_key,
-                fallback_supplement,
                 singleton,
             })
         } else {
@@ -308,8 +282,6 @@ fn data_struct_impl(attr: DataStructArgs, input: DeriveInput) -> TokenStream2 {
             marker_name,
             path_lit,
             fallback_by,
-            extension_key,
-            fallback_supplement,
             singleton,
         } = single_attr;
 
@@ -318,11 +290,10 @@ fn data_struct_impl(attr: DataStructArgs, input: DeriveInput) -> TokenStream2 {
                 Some(ref fallback_by) => fallback_by.value(),
                 None => "language (default)".to_string(),
             };
-            let extension_key_docs_str = match extension_key {
-                Some(ref extension_key) => extension_key.value(),
-                None => "none (default)".to_string(),
-            };
-            format!("Marker type for [`{}`]: \"{}\"\n\n- Fallback priority: {}\n- Extension keyword: {}", name, path_lit.value(), fallback_by_docs_str, extension_key_docs_str)
+            format!(
+                "Marker type for [`{name}`]: \"{}\"\n\n- Fallback priority: {fallback_by_docs_str}",
+                path_lit.value()
+            )
         } else {
             format!("Marker type for [`{name}`]")
         };
@@ -342,8 +313,8 @@ fn data_struct_impl(attr: DataStructArgs, input: DeriveInput) -> TokenStream2 {
                     "region" => {
                         quote! {icu_provider::_internal::LocaleFallbackPriority::Region}
                     }
-                    "collation" => {
-                        quote! {icu_provider::_internal::LocaleFallbackPriority::Collation}
+                    "script" => {
+                        quote! {icu_provider::_internal::LocaleFallbackPriority::Script}
                     }
                     "language" => {
                         quote! {icu_provider::_internal::LocaleFallbackPriority::Language}
@@ -353,31 +324,12 @@ fn data_struct_impl(attr: DataStructArgs, input: DeriveInput) -> TokenStream2 {
             } else {
                 quote! {icu_provider::_internal::LocaleFallbackPriority::const_default()}
             };
-            let extension_key_expr = if let Some(extension_path_lit) = extension_key {
-                quote! {Some(icu_provider::_internal::locale_core::extensions::unicode::key!(#extension_path_lit))}
-            } else {
-                quote! {None}
-            };
-            let fallback_supplement_expr = if let Some(fallback_supplement_lit) =
-                fallback_supplement
-            {
-                match fallback_supplement_lit.value().as_str() {
-                    "collation" => {
-                        quote! {Some(icu_provider::_internal::LocaleFallbackSupplement::Collation)}
-                    }
-                    _ => panic!("Invalid value for fallback_supplement"),
-                }
-            } else {
-                quote! {None}
-            };
             result.extend(quote!(
                 impl icu_provider::DataMarker for #marker_name {
                     const INFO: icu_provider::DataMarkerInfo = {
                         let mut info = icu_provider::DataMarkerInfo::from_path(icu_provider::marker::data_marker_path!(#path_str));
                         info.is_singleton = #singleton;
                         info.fallback_config.priority = #fallback_by_expr;
-                        info.fallback_config.extension_key = #extension_key_expr;
-                        info.fallback_config.fallback_supplement = #fallback_supplement_expr;
                         info
                     };
                 }
diff --git a/provider/core/macros/src/tests.rs b/provider/core/macros/src/tests.rs
index b6eeaededdd..b1483e96fe5 100644
--- a/provider/core/macros/src/tests.rs
+++ b/provider/core/macros/src/tests.rs
@@ -56,7 +56,7 @@ fn test_data_marker() {
             pub struct FooV1;
         ),
         quote!(
-            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: language (default)\n- Extension keyword: none (default)"]
+            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: language (default)"]
             pub struct BarV1Marker;
             impl icu_provider::DynamicDataMarker for BarV1Marker {
                 type Yokeable = FooV1;
@@ -66,8 +66,6 @@ fn test_data_marker() {
                     let mut info = icu_provider::DataMarkerInfo::from_path(icu_provider::marker::data_marker_path!("demo/bar@1"));
                     info.is_singleton = false;
                     info.fallback_config.priority = icu_provider::_internal::LocaleFallbackPriority::const_default();
-                    info.fallback_config.extension_key = None;
-                    info.fallback_config.fallback_supplement = None;
                     info
                 };
             }
@@ -95,7 +93,7 @@ fn test_multi_named_keyed_data_marker() {
             impl icu_provider::DynamicDataMarker for FooV1Marker {
                 type Yokeable = FooV1<'static>;
             }
-            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: language (default)\n- Extension keyword: none (default)"]
+            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: language (default)"]
             pub struct BarV1Marker;
             impl icu_provider::DynamicDataMarker for BarV1Marker {
                 type Yokeable = FooV1<'static>;
@@ -105,12 +103,10 @@ fn test_multi_named_keyed_data_marker() {
                     let mut info = icu_provider::DataMarkerInfo::from_path(icu_provider::marker::data_marker_path!("demo/bar@1"));
                     info.is_singleton = false;
                     info.fallback_config.priority = icu_provider::_internal::LocaleFallbackPriority::const_default();
-                    info.fallback_config.extension_key = None;
-                    info.fallback_config.fallback_supplement = None;
                     info
                 };
             }
-            #[doc = "Marker type for [`FooV1`]: \"demo/baz@1\"\n\n- Fallback priority: language (default)\n- Extension keyword: none (default)"]
+            #[doc = "Marker type for [`FooV1`]: \"demo/baz@1\"\n\n- Fallback priority: language (default)"]
             pub struct BazV1Marker;
             impl icu_provider::DynamicDataMarker for BazV1Marker {
                 type Yokeable = FooV1<'static>;
@@ -120,8 +116,6 @@ fn test_multi_named_keyed_data_marker() {
                     let mut info = icu_provider::DataMarkerInfo::from_path(icu_provider::marker::data_marker_path!("demo/baz@1"));
                     info.is_singleton = false;
                     info.fallback_config.priority = icu_provider::_internal::LocaleFallbackPriority::const_default();
-                    info.fallback_config.extension_key = None;
-                    info.fallback_config.fallback_supplement = None;
                     info
                 };
             }
@@ -137,14 +131,7 @@ fn test_attributes() {
     check(
         quote![
             FooV1Marker,
-            marker(
-                BarV1Marker,
-                "demo/bar@1",
-                fallback_by = "region",
-                extension_key = "ca",
-                fallback_supplement = "collation",
-                singleton,
-            ),
+            marker(BarV1Marker, "demo/bar@1", fallback_by = "region", singleton),
         ],
         quote!(
             pub struct FooV1<'data>;
@@ -155,7 +142,7 @@ fn test_attributes() {
             impl icu_provider::DynamicDataMarker for FooV1Marker {
                 type Yokeable = FooV1<'static>;
             }
-            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: region\n- Extension keyword: ca"]
+            #[doc = "Marker type for [`FooV1`]: \"demo/bar@1\"\n\n- Fallback priority: region"]
             pub struct BarV1Marker;
             impl icu_provider::DynamicDataMarker for BarV1Marker {
                 type Yokeable = FooV1<'static>;
@@ -165,8 +152,6 @@ fn test_attributes() {
                     let mut info = icu_provider::DataMarkerInfo::from_path(icu_provider::marker::data_marker_path!("demo/bar@1"));
                     info.is_singleton = true;
                     info.fallback_config.priority = icu_provider::_internal::LocaleFallbackPriority::Region;
-                    info.fallback_config.extension_key = Some(icu_provider::_internal::locale_core::extensions::unicode::key!("ca"));
-                    info.fallback_config.fallback_supplement = Some(icu_provider::_internal::LocaleFallbackSupplement::Collation);
                     info
                 };
             }
diff --git a/provider/core/src/fallback.rs b/provider/core/src/fallback.rs
index a1e196e8ae4..a52319a8735 100644
--- a/provider/core/src/fallback.rs
+++ b/provider/core/src/fallback.rs
@@ -7,8 +7,6 @@
 //! These options are consumed by the `LocaleFallbacker` in the `icu_locales` crate
 //! (or the `icu::locales` module), but are defined here because they are used by `DataMarkerInfo`.
 
-use icu_locale_core::extensions::unicode::Key;
-
 /// Hint for which subtag to prioritize during fallback.
 ///
 /// For example, `"en-US"` might fall back to either `"en"` or `"und-US"` depending
@@ -24,10 +22,6 @@ pub enum LocaleFallbackPriority {
     ///
     /// For example, `"en-US"` should go to `"und-US"` and then `"und"`.
     Region,
-    /// Collation-specific fallback rules. Similar to language priority.
-    ///
-    /// For example, `"zh-Hant"` goes to `"zh"` before `"und"`.
-    Collation,
 }
 
 impl LocaleFallbackPriority {
@@ -43,14 +37,6 @@ impl Default for LocaleFallbackPriority {
     }
 }
 
-/// What additional data is required to load when performing fallback.
-#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
-#[non_exhaustive]
-pub enum LocaleFallbackSupplement {
-    /// Collation supplement
-    Collation,
-}
-
 /// Configuration settings for a particular fallback operation.
 #[derive(Debug, Clone, PartialEq, Eq, Copy)]
 #[non_exhaustive]
@@ -115,73 +101,6 @@ pub struct LocaleFallbackConfig {
     /// assert_eq!(fallback_iterator.get(), &locale!("und").into());
     /// ```
     pub priority: LocaleFallbackPriority,
-    /// An extension keyword to retain during locale fallback.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use icu::locale::locale;
-    /// use icu::locale::fallback::LocaleFallbackConfig;
-    /// use icu::locale::LocaleFallbacker;
-    ///
-    /// // Set up the fallback iterator.
-    /// let fallbacker = LocaleFallbacker::new();
-    /// let mut config = LocaleFallbackConfig::default();
-    /// config.extension_key = Some(icu::locale::extensions::unicode::key!("nu"));
-    /// let mut fallback_iterator = fallbacker
-    ///     .for_config(config)
-    ///     .fallback_for(locale!("ar-EG-u-nu-latn").into());
-    ///
-    /// // Run the algorithm and check the results.
-    /// assert_eq!(fallback_iterator.get(), &locale!("ar-EG-u-nu-latn").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("ar-EG").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("ar-u-nu-latn").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("ar").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("und").into());
-    /// ```
-    pub extension_key: Option<Key>,
-    /// Fallback supplement data key to customize fallback rules.
-    ///
-    /// For example, most data keys for collation add additional parent locales, such as
-    /// "yue" to "zh-Hant", and data used for the `"-u-co"` extension keyword fallback.
-    ///
-    /// Currently the only supported fallback supplement is `LocaleFallbackSupplement::Collation`, but more may be
-    /// added in the future.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use icu::locale::locale;
-    /// use icu::locale::fallback::LocaleFallbackConfig;
-    /// use icu::locale::fallback::LocaleFallbackPriority;
-    /// use icu::locale::fallback::LocaleFallbackSupplement;
-    /// use icu::locale::LocaleFallbacker;
-    ///
-    /// // Set up the fallback iterator.
-    /// let fallbacker = LocaleFallbacker::new();
-    /// let mut config = LocaleFallbackConfig::default();
-    /// config.priority = LocaleFallbackPriority::Collation;
-    /// config.fallback_supplement = Some(LocaleFallbackSupplement::Collation);
-    /// let mut fallback_iterator = fallbacker
-    ///     .for_config(config)
-    ///     .fallback_for(locale!("yue-HK").into());
-    ///
-    /// // Run the algorithm and check the results.
-    /// assert_eq!(fallback_iterator.get(), &locale!("yue-HK").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("yue").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("zh-Hant").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("zh").into());
-    /// fallback_iterator.step();
-    /// assert_eq!(fallback_iterator.get(), &locale!("und").into());
-    /// ```
-    pub fallback_supplement: Option<LocaleFallbackSupplement>,
 }
 
 impl LocaleFallbackConfig {
@@ -189,8 +108,6 @@ impl LocaleFallbackConfig {
     pub const fn const_default() -> Self {
         Self {
             priority: LocaleFallbackPriority::const_default(),
-            extension_key: None,
-            fallback_supplement: None,
         }
     }
 }
diff --git a/provider/core/src/lib.rs b/provider/core/src/lib.rs
index b1c9c5068f0..ad4d2163427 100644
--- a/provider/core/src/lib.rs
+++ b/provider/core/src/lib.rs
@@ -185,9 +185,7 @@ mod fallback;
 
 #[doc(hidden)] // macro use
 pub mod _internal {
-    pub use super::fallback::{
-        LocaleFallbackConfig, LocaleFallbackPriority, LocaleFallbackSupplement,
-    };
+    pub use super::fallback::{LocaleFallbackConfig, LocaleFallbackPriority};
     pub use icu_locale_core as locale_core;
 
     #[cfg(feature = "logging")]
diff --git a/provider/data/locale/data/collation_fallback_supplement_v1_marker.rs.data b/provider/data/locale/data/collation_fallback_supplement_v1_marker.rs.data
deleted file mode 100644
index e99901073eb..00000000000
--- a/provider/data/locale/data/collation_fallback_supplement_v1_marker.rs.data
+++ /dev/null
@@ -1,52 +0,0 @@
-// @generated
-/// Implement `DataProvider<CollationFallbackSupplementV1Marker>` on the given struct using the data
-/// hardcoded in this file. This allows the struct to be used with
-/// `icu`'s `_unstable` constructors.
-///
-/// Using this implementation will embed the following data in the binary's data segment:
-/// * 804B[^1] for the singleton data struct
-///
-/// [^1]: these numbers can be smaller in practice due to linker deduplication
-#[doc(hidden)]
-#[macro_export]
-macro_rules! __impl_collation_fallback_supplement_v1_marker {
-    ($ provider : ty) => {
-        #[clippy::msrv = "1.70"]
-        const _: () = <$provider>::MUST_USE_MAKE_PROVIDER_MACRO;
-        #[clippy::msrv = "1.70"]
-        impl $provider {
-            #[doc(hidden)]
-            pub const SINGLETON_COLLATION_FALLBACK_SUPPLEMENT_V1_MARKER: &'static <icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DynamicDataMarker>::Yokeable = &icu::locale::provider::LocaleFallbackSupplementV1 {
-                parents: unsafe {
-                    #[allow(unused_unsafe)]
-                    zerovec::ZeroMap::from_parts_unchecked(unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x1D\0\0\0\0\0\x07\0\x0E\0\x15\0\x1C\0#\0*\x001\08\0?\0F\0M\0T\0[\0b\0i\0p\0z\0\x81\0\x88\0\x8F\0\x96\0\x9D\0\xA4\0\xA7\0\xAD\0\xB5\0\xC0\0\xC8\0az-Arabaz-Cyrlbs-Cyrlen-Dsrten-Shawff-Adlmff-Arabha-Arabhi-Latnkk-Arabku-Arabky-Arabky-Latnml-Arabmn-Mongpa-Arabsr-Cyrl-MEsr-Latnug-Cyrluz-Arabuz-Cyrlwo-Arabyo-Arabyueyue-CNyue-Hansyue-Hans-CNyue-Hantzh-Hant") }, unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"az\0\0\0\0\0\0\0\0\0\0az\0\0\0\0\0\0\0\0\0\0bs\0\0\0\0\0\0\0\0\0\0en\0\0\0\0\0\0\0\0\0\0en\0\0\0\0\0\0\0\0\0\0ff\0\0\0\0\0\0\0\0\0\0ff\0\0\0\0\0\0\0\0\0\0ha\0\0\0\0\0\0\0\0\0\0hi\0\0\0\0\0\0\0\0\0\0kk\0\0\0\0\0\0\0\0\0\0ku\0\0\0\0\0\0\0\0\0\0ky\0\0\0\0\0\0\0\0\0\0ky\0\0\0\0\0\0\0\0\0\0ml\0\0\0\0\0\0\0\0\0\0mn\0\0\0\0\0\0\0\0\0\0pa\0\0\0\0\0\0\0\0\0\0sr\0\0\0\0\0\0\x01ME\0sr\0\0\0\0\0\0\0\0\0\0ug\0\0\0\0\0\0\0\0\0\0uz\0\0\0\0\0\0\0\0\0\0uz\0\0\0\0\0\0\0\0\0\0wo\0\0\0\0\0\0\0\0\0\0yo\0\0\0\0\0\0\0\0\0\0zh\0\x01Hant\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hant\0\0\0\0zh\0\0\0\0\0\0\0\0\0\0") })
-                },
-                unicode_extension_defaults: unsafe {
-                    #[allow(unused_unsafe)]
-                    zerovec::ZeroMap2d::from_parts_unchecked(unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"co") }, unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"\x02\0\0\0") }, unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x02\0\0\0\0\0\x02\0zhzh-Hant") }, unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x02\0\0\0\0\0\x06\0pinyinstroke") })
-                },
-            };
-        }
-        #[clippy::msrv = "1.70"]
-        impl icu_provider::DataProvider<icu::locale::provider::CollationFallbackSupplementV1Marker> for $provider {
-            fn load(&self, req: icu_provider::DataRequest) -> Result<icu_provider::DataResponse<icu::locale::provider::CollationFallbackSupplementV1Marker>, icu_provider::DataError> {
-                if req.id.locale.is_und() {
-                    Ok(icu_provider::DataResponse { payload: icu_provider::DataPayload::from_static_ref(Self::SINGLETON_COLLATION_FALLBACK_SUPPLEMENT_V1_MARKER), metadata: Default::default() })
-                } else {
-                    Err(icu_provider::DataErrorKind::InvalidRequest.with_req(<icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DataMarker>::INFO, req))
-                }
-            }
-        }
-    };
-    ($ provider : ty , ITER) => {
-        __impl_collation_fallback_supplement_v1_marker!($provider);
-        #[clippy::msrv = "1.70"]
-        impl icu_provider::IterableDataProvider<icu::locale::provider::CollationFallbackSupplementV1Marker> for $provider {
-            fn iter_ids(&self) -> Result<std::collections::BtreeSet<icu_provider::DataIdentifierCow<'static>>, icu_provider::DataError> {
-                Ok([Default::default()].into_iter().collect())
-            }
-        }
-    };
-}
-#[doc(inline)]
-pub use __impl_collation_fallback_supplement_v1_marker as impl_collation_fallback_supplement_v1_marker;
diff --git a/provider/data/locale/data/mod.rs b/provider/data/locale/data/mod.rs
index b1177ad4de5..f7c9aec7fa7 100644
--- a/provider/data/locale/data/mod.rs
+++ b/provider/data/locale/data/mod.rs
@@ -1,7 +1,6 @@
 // @generated
 include!("locale_fallback_likely_subtags_v1_marker.rs.data");
 include!("locale_fallback_parents_v1_marker.rs.data");
-include!("collation_fallback_supplement_v1_marker.rs.data");
 include!("aliases_v2_marker.rs.data");
 include!("likely_subtags_extended_v1_marker.rs.data");
 include!("likely_subtags_for_language_v1_marker.rs.data");
@@ -38,7 +37,6 @@ macro_rules! impl_data_provider {
         make_provider!($provider);
         impl_locale_fallback_likely_subtags_v1_marker!($provider);
         impl_locale_fallback_parents_v1_marker!($provider);
-        impl_collation_fallback_supplement_v1_marker!($provider);
         impl_aliases_v2_marker!($provider);
         impl_likely_subtags_extended_v1_marker!($provider);
         impl_likely_subtags_for_language_v1_marker!($provider);
@@ -55,7 +53,6 @@ macro_rules! impl_any_provider {
                 match marker.path.hashed() {
                     h if h == <icu::locale::provider::LocaleFallbackLikelySubtagsV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LocaleFallbackLikelySubtagsV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LocaleFallbackParentsV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LocaleFallbackParentsV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
-                    h if h == <icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::CollationFallbackSupplementV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::AliasesV2Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::AliasesV2Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LikelySubtagsExtendedV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LikelySubtagsExtendedV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LikelySubtagsForLanguageV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LikelySubtagsForLanguageV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
diff --git a/provider/data/locale/fingerprints.csv b/provider/data/locale/fingerprints.csv
index b9e5b63c900..c346ffbe7a9 100644
--- a/provider/data/locale/fingerprints.csv
+++ b/provider/data/locale/fingerprints.csv
@@ -1,6 +1,5 @@
 fallback/likelysubtags@1, <singleton>, 2228B, a6ec0551218ff716
 fallback/parents@1, <singleton>, 2597B, 8f3b5fb7bff27d97
-fallback/supplement/co@1, <singleton>, 804B, 986f688c39a3d558
 locid_transform/aliases@2, <singleton>, 8623B, 2c1368fc48eb6158
 locid_transform/likelysubtags_ext@1, <singleton>, 75788B, 681a300516da7f39
 locid_transform/likelysubtags_l@1, <singleton>, 2230B, a7c40445e0c19c21
diff --git a/provider/data/locale/stubdata/collation_fallback_supplement_v1_marker.rs.data b/provider/data/locale/stubdata/collation_fallback_supplement_v1_marker.rs.data
deleted file mode 100644
index e99901073eb..00000000000
--- a/provider/data/locale/stubdata/collation_fallback_supplement_v1_marker.rs.data
+++ /dev/null
@@ -1,52 +0,0 @@
-// @generated
-/// Implement `DataProvider<CollationFallbackSupplementV1Marker>` on the given struct using the data
-/// hardcoded in this file. This allows the struct to be used with
-/// `icu`'s `_unstable` constructors.
-///
-/// Using this implementation will embed the following data in the binary's data segment:
-/// * 804B[^1] for the singleton data struct
-///
-/// [^1]: these numbers can be smaller in practice due to linker deduplication
-#[doc(hidden)]
-#[macro_export]
-macro_rules! __impl_collation_fallback_supplement_v1_marker {
-    ($ provider : ty) => {
-        #[clippy::msrv = "1.70"]
-        const _: () = <$provider>::MUST_USE_MAKE_PROVIDER_MACRO;
-        #[clippy::msrv = "1.70"]
-        impl $provider {
-            #[doc(hidden)]
-            pub const SINGLETON_COLLATION_FALLBACK_SUPPLEMENT_V1_MARKER: &'static <icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DynamicDataMarker>::Yokeable = &icu::locale::provider::LocaleFallbackSupplementV1 {
-                parents: unsafe {
-                    #[allow(unused_unsafe)]
-                    zerovec::ZeroMap::from_parts_unchecked(unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x1D\0\0\0\0\0\x07\0\x0E\0\x15\0\x1C\0#\0*\x001\08\0?\0F\0M\0T\0[\0b\0i\0p\0z\0\x81\0\x88\0\x8F\0\x96\0\x9D\0\xA4\0\xA7\0\xAD\0\xB5\0\xC0\0\xC8\0az-Arabaz-Cyrlbs-Cyrlen-Dsrten-Shawff-Adlmff-Arabha-Arabhi-Latnkk-Arabku-Arabky-Arabky-Latnml-Arabmn-Mongpa-Arabsr-Cyrl-MEsr-Latnug-Cyrluz-Arabuz-Cyrlwo-Arabyo-Arabyueyue-CNyue-Hansyue-Hans-CNyue-Hantzh-Hant") }, unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"az\0\0\0\0\0\0\0\0\0\0az\0\0\0\0\0\0\0\0\0\0bs\0\0\0\0\0\0\0\0\0\0en\0\0\0\0\0\0\0\0\0\0en\0\0\0\0\0\0\0\0\0\0ff\0\0\0\0\0\0\0\0\0\0ff\0\0\0\0\0\0\0\0\0\0ha\0\0\0\0\0\0\0\0\0\0hi\0\0\0\0\0\0\0\0\0\0kk\0\0\0\0\0\0\0\0\0\0ku\0\0\0\0\0\0\0\0\0\0ky\0\0\0\0\0\0\0\0\0\0ky\0\0\0\0\0\0\0\0\0\0ml\0\0\0\0\0\0\0\0\0\0mn\0\0\0\0\0\0\0\0\0\0pa\0\0\0\0\0\0\0\0\0\0sr\0\0\0\0\0\0\x01ME\0sr\0\0\0\0\0\0\0\0\0\0ug\0\0\0\0\0\0\0\0\0\0uz\0\0\0\0\0\0\0\0\0\0uz\0\0\0\0\0\0\0\0\0\0wo\0\0\0\0\0\0\0\0\0\0yo\0\0\0\0\0\0\0\0\0\0zh\0\x01Hant\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hans\0\0\0\0zh\0\x01Hant\0\0\0\0zh\0\0\0\0\0\0\0\0\0\0") })
-                },
-                unicode_extension_defaults: unsafe {
-                    #[allow(unused_unsafe)]
-                    zerovec::ZeroMap2d::from_parts_unchecked(unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"co") }, unsafe { zerovec::ZeroVec::from_bytes_unchecked(b"\x02\0\0\0") }, unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x02\0\0\0\0\0\x02\0zhzh-Hant") }, unsafe { zerovec::VarZeroVec::from_bytes_unchecked(b"\x02\0\0\0\0\0\x06\0pinyinstroke") })
-                },
-            };
-        }
-        #[clippy::msrv = "1.70"]
-        impl icu_provider::DataProvider<icu::locale::provider::CollationFallbackSupplementV1Marker> for $provider {
-            fn load(&self, req: icu_provider::DataRequest) -> Result<icu_provider::DataResponse<icu::locale::provider::CollationFallbackSupplementV1Marker>, icu_provider::DataError> {
-                if req.id.locale.is_und() {
-                    Ok(icu_provider::DataResponse { payload: icu_provider::DataPayload::from_static_ref(Self::SINGLETON_COLLATION_FALLBACK_SUPPLEMENT_V1_MARKER), metadata: Default::default() })
-                } else {
-                    Err(icu_provider::DataErrorKind::InvalidRequest.with_req(<icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DataMarker>::INFO, req))
-                }
-            }
-        }
-    };
-    ($ provider : ty , ITER) => {
-        __impl_collation_fallback_supplement_v1_marker!($provider);
-        #[clippy::msrv = "1.70"]
-        impl icu_provider::IterableDataProvider<icu::locale::provider::CollationFallbackSupplementV1Marker> for $provider {
-            fn iter_ids(&self) -> Result<std::collections::BtreeSet<icu_provider::DataIdentifierCow<'static>>, icu_provider::DataError> {
-                Ok([Default::default()].into_iter().collect())
-            }
-        }
-    };
-}
-#[doc(inline)]
-pub use __impl_collation_fallback_supplement_v1_marker as impl_collation_fallback_supplement_v1_marker;
diff --git a/provider/data/locale/stubdata/mod.rs b/provider/data/locale/stubdata/mod.rs
index b1177ad4de5..f7c9aec7fa7 100644
--- a/provider/data/locale/stubdata/mod.rs
+++ b/provider/data/locale/stubdata/mod.rs
@@ -1,7 +1,6 @@
 // @generated
 include!("locale_fallback_likely_subtags_v1_marker.rs.data");
 include!("locale_fallback_parents_v1_marker.rs.data");
-include!("collation_fallback_supplement_v1_marker.rs.data");
 include!("aliases_v2_marker.rs.data");
 include!("likely_subtags_extended_v1_marker.rs.data");
 include!("likely_subtags_for_language_v1_marker.rs.data");
@@ -38,7 +37,6 @@ macro_rules! impl_data_provider {
         make_provider!($provider);
         impl_locale_fallback_likely_subtags_v1_marker!($provider);
         impl_locale_fallback_parents_v1_marker!($provider);
-        impl_collation_fallback_supplement_v1_marker!($provider);
         impl_aliases_v2_marker!($provider);
         impl_likely_subtags_extended_v1_marker!($provider);
         impl_likely_subtags_for_language_v1_marker!($provider);
@@ -55,7 +53,6 @@ macro_rules! impl_any_provider {
                 match marker.path.hashed() {
                     h if h == <icu::locale::provider::LocaleFallbackLikelySubtagsV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LocaleFallbackLikelySubtagsV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LocaleFallbackParentsV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LocaleFallbackParentsV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
-                    h if h == <icu::locale::provider::CollationFallbackSupplementV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::CollationFallbackSupplementV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::AliasesV2Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::AliasesV2Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LikelySubtagsExtendedV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LikelySubtagsExtendedV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
                     h if h == <icu::locale::provider::LikelySubtagsForLanguageV1Marker as icu_provider::DataMarker>::INFO.path.hashed() => icu_provider::DataProvider::<icu::locale::provider::LikelySubtagsForLanguageV1Marker>::load(self, req).map(icu_provider::DataResponse::wrap_into_any_response),
diff --git a/provider/registry/src/lib.rs b/provider/registry/src/lib.rs
index 9430b318d02..1656d03893b 100644
--- a/provider/registry/src/lib.rs
+++ b/provider/registry/src/lib.rs
@@ -77,7 +77,6 @@ macro_rules! registry(
             icu::list::provider::UnitListV2Marker = "list/unit@2",
             icu::locale::provider::AliasesV1Marker = "locid_transform/aliases@1",
             icu::locale::provider::AliasesV2Marker = "locid_transform/aliases@2",
-            icu::locale::provider::CollationFallbackSupplementV1Marker = "fallback/supplement/co@1",
             icu::locale::provider::LikelySubtagsV1Marker = "locid_transform/likelysubtags@1",
             icu::locale::provider::LikelySubtagsExtendedV1Marker = "locid_transform/likelysubtags_ext@1",
             icu::locale::provider::LikelySubtagsForLanguageV1Marker = "locid_transform/likelysubtags_l@1",
diff --git a/provider/source/data/debug/fallback/supplement/co@1/und.json b/provider/source/data/debug/fallback/supplement/co@1/und.json
deleted file mode 100644
index e7a671c3123..00000000000
--- a/provider/source/data/debug/fallback/supplement/co@1/und.json
+++ /dev/null
@@ -1,50 +0,0 @@
-{
-  "parents": {
-    "sr-Cyrl-ME": [
-      "sr",
-      null,
-      "ME"
-    ],
-    "sr-Latn": [
-      "sr",
-      null,
-      null
-    ],
-    "yue": [
-      "zh",
-      "Hant",
-      null
-    ],
-    "yue-CN": [
-      "zh",
-      "Hans",
-      null
-    ],
-    "yue-Hans": [
-      "zh",
-      "Hans",
-      null
-    ],
-    "yue-Hans-CN": [
-      "zh",
-      "Hans",
-      null
-    ],
-    "yue-Hant": [
-      "zh",
-      "Hant",
-      null
-    ],
-    "zh-Hant": [
-      "zh",
-      null,
-      null
-    ]
-  },
-  "unicode_extension_defaults": {
-    "co": {
-      "zh": "pinyin",
-      "zh-Hant": "stroke"
-    }
-  }
-}
diff --git a/provider/source/src/collator/mod.rs b/provider/source/src/collator/mod.rs
index 4d375b11f91..730d22bf29a 100644
--- a/provider/source/src/collator/mod.rs
+++ b/provider/source/src/collator/mod.rs
@@ -9,106 +9,15 @@ use crate::IterableDataProviderCached;
 use crate::SourceDataProvider;
 use icu::collator::provider::*;
 use icu::collections::codepointtrie::CodePointTrie;
-use icu::locale::provider::CollationFallbackSupplementV1Marker;
-use icu::locale::provider::LocaleFallbackSupplementV1;
 use icu::locale::subtags::language;
-use icu::locale::subtags::Language;
-use icu::locale::subtags::Region;
-use icu::locale::subtags::Script;
 use icu_provider::prelude::*;
 use std::collections::HashSet;
 use std::convert::TryFrom;
 use writeable::Writeable;
-use zerovec::ule::UnvalidatedStr;
 use zerovec::ZeroVec;
 
 mod collator_serde;
 
-impl DataProvider<CollationFallbackSupplementV1Marker> for SourceDataProvider {
-    fn load(
-        &self,
-        req: DataRequest,
-    ) -> Result<DataResponse<CollationFallbackSupplementV1Marker>, DataError> {
-        self.check_req::<CollationFallbackSupplementV1Marker>(req)?;
-
-        let parent_locales = &self
-            .cldr()?
-            .core()
-            .read_and_parse::<crate::cldr_serde::parent_locales::Resource>(
-                "supplemental/parentLocales.json",
-            )?
-            .supplemental
-            .parent_locales;
-
-        let additional = if parent_locales
-            .rules
-            .collations
-            .as_ref()
-            .map(|c| &c.non_likely_scripts)
-            != Some(&String::from("root"))
-        {
-            let collation_locales = self
-                .icuexport()?
-                .list(&format!("collation/{}", self.collation_han_database()))?
-                .filter_map(|s| Some(file_name_to_id(s.rsplit_once('_')?.0)?.locale.language()))
-                .collect::<HashSet<_>>();
-
-            parent_locales
-                .parent_locale
-                .iter()
-                .filter(|(k, _)| collation_locales.contains(&k.language))
-                .filter(|(from, to)| {
-                    // Script gets removed while language changes. For collation we want to insert the script-removal as its
-                    // own step.
-                    from.script.is_some() && to.script.is_none() && from.language != to.language
-                })
-                .map(|(from, _)| (from.to_string(), (from.language, None, from.region)))
-                .collect()
-        } else {
-            HashSet::new()
-        };
-
-        let parents = additional
-            .iter()
-            .map(|(k, v)| (UnvalidatedStr::from_str(k), *v))
-            .chain(parent_locales.collations.iter().map(|(from, to)| {
-                (
-                    <&UnvalidatedStr>::from(from.as_str()),
-                    <(Language, Option<Script>, Option<Region>)>::from(to),
-                )
-            }))
-            .collect();
-
-        let data = LocaleFallbackSupplementV1 {
-            parents,
-            unicode_extension_defaults: [
-                (
-                    icu::locale::extensions::unicode::key!("co"),
-                    <&UnvalidatedStr>::from("zh"),
-                    <&UnvalidatedStr>::from("pinyin"),
-                ),
-                (
-                    icu::locale::extensions::unicode::key!("co"),
-                    <&UnvalidatedStr>::from("zh-Hant"),
-                    <&UnvalidatedStr>::from("stroke"),
-                ),
-            ]
-            .into_iter()
-            .collect(),
-        };
-        Ok(DataResponse {
-            metadata: Default::default(),
-            payload: DataPayload::from_owned(data),
-        })
-    }
-}
-
-impl crate::IterableDataProviderCached<CollationFallbackSupplementV1Marker> for SourceDataProvider {
-    fn iter_ids_cached(&self) -> Result<HashSet<DataIdentifierCow<'static>>, DataError> {
-        Ok(HashSet::from_iter([Default::default()]))
-    }
-}
-
 fn id_to_file_name(id: &DataIdentifierBorrowed) -> String {
     let mut s = if id.locale.is_und() {
         "root".to_owned()