fix(cli): reduce memory usage during SDK generation by skipping dynamic IR

packages/cli/cli/src/cli.ts

@@ -17,7 +17,9 @@ import { LOG_LEVELS, LogLevel } from "@fern-api/logger";
 import { askToLogin, login, logout } from "@fern-api/login";
 import { protocGenFern } from "@fern-api/protoc-gen-fern";
 import { FernCliError, LoggableFernCliError } from "@fern-api/task-context";
+import { spawnSync } from "child_process";
 import getPort from "get-port";
+import v8 from "v8";
 import { Argv } from "yargs";
 import { hideBin } from "yargs/helpers";
 import yargs from "yargs/yargs";
@@ -63,6 +65,32 @@ import { FERN_CWD_ENV_VAR } from "./cwd";
 import { rerunFernCliAtVersion } from "./rerunFernCliAtVersion";
 import { RUNTIME } from "./runtime";
 
+// Increase heap size for large API generation if not already set
+// Skip during tests to avoid breaking test execution
+const DESIRED_HEAP_SIZE_MB = 8192; // 8GB
+const isTestEnvironment = process.env.VITEST != null || process.env.NODE_ENV === "test";
+const heapStats = v8.getHeapStatistics();
+const currentHeapLimitMB = Math.floor(heapStats.heap_size_limit / (1024 * 1024));
+
+// Only re-spawn if:
+// 1. Not in test environment
+// 2. Heap is below desired size
+// 3. Haven't already tried re-spawning
+if (!isTestEnvironment && currentHeapLimitMB < DESIRED_HEAP_SIZE_MB && process.env.FERN_HEAP_INCREASED !== "true") {
+    const result = spawnSync(
+        process.execPath,
+        [`--max-old-space-size=${DESIRED_HEAP_SIZE_MB}`, ...process.argv.slice(1)],
+        {
+            stdio: "inherit",
+            env: {
+                ...process.env,
+                FERN_HEAP_INCREASED: "true"
+            }
+        }
+    );
+    process.exit(result.status ?? 1);
+}
+
 void runCli();
 
 const USE_NODE_18_OR_ABOVE_MESSAGE = "The Fern CLI requires Node 18+ or above.";

packages/cli/cli/versions.yml

@@ -1,4 +1,15 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
+- version: 3.58.1
+  changelogEntry:
+    - summary: |
+        Fix memory issues during SDK generation for large APIs by skipping dynamic IR generation during the main IR generation phase. Dynamic IR is now only generated when needed for uploading to FDR, reducing peak memory usage significantly.
+      type: fix
+    - summary: |
+        Automatically increase Node.js heap size to 8GB for large API generation. The CLI now detects when the heap limit is below 8GB and re-spawns with increased memory to prevent out-of-memory errors.
+      type: fix
+  createdAt: "2026-02-03"
+  irVersion: 63
+
 - version: 3.58.0
   changelogEntry:
     - summary: |

packages/cli/generation/ir-generator/src/generateIntermediateRepresentation.ts

@@ -76,6 +76,7 @@ export declare namespace generateIntermediateRepresentation {
         sourceResolver: SourceResolver;
         fdrApiDefinitionId?: string;
         disableDynamicExamples?: boolean;
+        skipDynamicIr?: boolean;
         dynamicGeneratorConfig?: dynamic.GeneratorConfig;
         generationMetadata?: FernIr.GenerationMetadata;
     }
@@ -94,6 +95,7 @@ export function generateIntermediateRepresentation({
     fdrApiDefinitionId,
     sourceResolver,
     disableDynamicExamples,
+    skipDynamicIr,
     dynamicGeneratorConfig,
     generationMetadata
 }: generateIntermediateRepresentation.Args): IntermediateRepresentation {
@@ -551,13 +553,15 @@ export function generateIntermediateRepresentation({
 
     return {
         ...finalIR,
-        dynamic: convertIrToDynamicSnippetsIr({
-            ir: finalIR,
-            generatorConfig: dynamicGeneratorConfig,
-            disableExamples: disableDynamicExamples,
-            generationLanguage,
-            smartCasing
-        })
+        dynamic: skipDynamicIr
+            ? undefined
+            : convertIrToDynamicSnippetsIr({
+                  ir: finalIR,
+                  generatorConfig: dynamicGeneratorConfig,
+                  disableExamples: disableDynamicExamples,
+                  generationLanguage,
+                  smartCasing
+              })
     };
 }
 

packages/cli/generation/remote-generation/remote-workspace-runner/src/runRemoteGenerationForGenerator.ts

@@ -96,6 +96,7 @@ export async function runRemoteGenerationForGenerator({
         context: interactiveTaskContext,
         sourceResolver: new SourceResolverImpl(interactiveTaskContext, workspace),
         dynamicGeneratorConfig,
+        skipDynamicIr: true,
         generationMetadata: {
             cliVersion: workspace.cliVersion,
             generatorName: generatorInvocation.name,