diff --git a/src/ethereum_test_tools/spec/blockchain_test.py b/src/ethereum_test_tools/spec/blockchain_test.py
index e82eac4a00..2c2bc5701f 100644
--- a/src/ethereum_test_tools/spec/blockchain_test.py
+++ b/src/ethereum_test_tools/spec/blockchain_test.py
@@ -159,9 +159,9 @@ def make_block(
                 alloc=previous_alloc,
                 txs=to_json(txs),
                 env=to_json(env),
-                fork=fork,
-                block_number=Number(env.number),
-                block_timestamp=Number(env.timestamp),
+                fork_name=fork.fork(
+                    block_number=Number(env.number), timestamp=Number(env.timestamp)
+                ),
                 chain_id=chain_id,
                 reward=fork.get_reward(Number(env.number), Number(env.timestamp)),
                 eips=eips,
diff --git a/src/ethereum_test_tools/spec/state_test.py b/src/ethereum_test_tools/spec/state_test.py
index e710478149..ac1e19a45b 100644
--- a/src/ethereum_test_tools/spec/state_test.py
+++ b/src/ethereum_test_tools/spec/state_test.py
@@ -126,9 +126,7 @@ def make_blocks(
             alloc=to_json(Alloc(self.pre)),
             txs=to_json(txs),
             env=to_json(env),
-            fork=fork,
-            block_number=Number(env.number),
-            block_timestamp=Number(env.timestamp),
+            fork_name=fork.fork(block_number=Number(env.number), timestamp=Number(env.timestamp)),
             chain_id=chain_id,
             reward=fork.get_reward(Number(env.number), Number(env.timestamp)),
             eips=eips,
diff --git a/src/evm_transition_tool/besu.py b/src/evm_transition_tool/besu.py
index 15f859381a..f7656b953d 100644
--- a/src/evm_transition_tool/besu.py
+++ b/src/evm_transition_tool/besu.py
@@ -81,12 +81,11 @@ def evaluate(
         alloc: Any,
         txs: Any,
         env: Any,
-        fork: Fork,
-        block_number: int,
-        block_timestamp: int,
+        fork_name: str,
         chain_id: int = 1,
         reward: int = 0,
         eips: Optional[List[int]] = None,
+        debug_output_path: str = "",
     ) -> Tuple[Dict[str, Any], Dict[str, Any]]:
         """
         Executes `evm t8n` with the specified arguments.
@@ -94,7 +93,6 @@ def evaluate(
         if not self.process:
             self.start_server()
 
-        fork_name = fork.fork(block_number, block_timestamp)
         if eips is not None:
             fork_name = "+".join([fork_name] + [str(eip) for eip in eips])
 
diff --git a/src/evm_transition_tool/evmone.py b/src/evm_transition_tool/evmone.py
index 7b6d25bf3f..581903f977 100644
--- a/src/evm_transition_tool/evmone.py
+++ b/src/evm_transition_tool/evmone.py
@@ -50,9 +50,7 @@ def evaluate(
         alloc: Any,
         txs: Any,
         env: Any,
-        fork: Fork,
-        block_number: int,
-        block_timestamp: int,
+        fork_name: str,
         chain_id: int = 1,
         reward: int = 0,
         eips: Optional[List[int]] = None,
@@ -61,7 +59,6 @@ def evaluate(
         """
         Executes `evmone-t8n` with the specified arguments.
         """
-        fork_name = fork.fork(block_number, block_timestamp)
         if eips is not None:
             fork_name = "+".join([fork_name] + [str(eip) for eip in eips])
 
diff --git a/src/evm_transition_tool/geth.py b/src/evm_transition_tool/geth.py
index e2183c8306..dcab8b58f0 100644
--- a/src/evm_transition_tool/geth.py
+++ b/src/evm_transition_tool/geth.py
@@ -49,9 +49,7 @@ def evaluate(
         alloc: Any,
         txs: Any,
         env: Any,
-        fork: Fork,
-        block_number: int,
-        block_timestamp: int,
+        fork_name: str,
         chain_id: int = 1,
         reward: int = 0,
         eips: Optional[List[int]] = None,
@@ -60,7 +58,6 @@ def evaluate(
         """
         Executes `evm t8n` with the specified arguments.
         """
-        fork_name = fork.fork(block_number, block_timestamp)
         if eips is not None:
             fork_name = "+".join([fork_name] + [str(eip) for eip in eips])
 
diff --git a/src/evm_transition_tool/tests/test_evaluate.py b/src/evm_transition_tool/tests/test_evaluate.py
index 5e18886d6c..0513dc62a9 100644
--- a/src/evm_transition_tool/tests/test_evaluate.py
+++ b/src/evm_transition_tool/tests/test_evaluate.py
@@ -112,16 +112,17 @@ def test_evm_t8n(t8n: TransitionTool, test_dir: str) -> None:
         print(expected_path)
         alloc = json.load(alloc)
         txs = json.load(txs)
-        env = json.load(env)
+        env_json = json.load(env)
         expected = json.load(exp)
 
         result_alloc, result = t8n.evaluate(
             alloc=alloc,
             txs=txs,
-            env=env,
-            fork=Berlin,
-            block_number=0,
-            block_timestamp=0,
+            env=env_json,
+            fork_name=Berlin.fork(
+                block_number=int(env_json["currentNumber"], 0),
+                timestamp=int(env_json["currentTimestamp"], 0),
+            ),
         )
         print(result)
         assert result_alloc == expected.get("alloc")
diff --git a/src/evm_transition_tool/transition_tool.py b/src/evm_transition_tool/transition_tool.py
index 4910f4d625..5093e7c8e7 100644
--- a/src/evm_transition_tool/transition_tool.py
+++ b/src/evm_transition_tool/transition_tool.py
@@ -154,9 +154,7 @@ def evaluate(
         alloc: Any,
         txs: Any,
         env: Any,
-        fork: Fork,
-        block_number: int,
-        block_timestamp: int,
+        fork_name: str,
         chain_id: int = 1,
         reward: int = 0,
         eips: Optional[List[int]] = None,
@@ -232,9 +230,7 @@ def calc_state_root(self, *, alloc: Any, fork: Fork, debug_output_path: str = ""
             alloc=alloc,
             txs=[],
             env=env,
-            fork=fork,
-            block_number=0,
-            block_timestamp=0,
+            fork_name=fork.fork(block_number=0, timestamp=0),
             debug_output_path=debug_output_path,
         )
         state_root = result.get("stateRoot")
@@ -276,9 +272,7 @@ def calc_withdrawals_root(
             alloc={},
             txs=[],
             env=env,
-            fork=fork,
-            block_number=0,
-            block_timestamp=0,
+            fork_name=fork.fork(block_number=0, timestamp=0),
             debug_output_path=debug_output_path,
         )
         withdrawals_root = result.get("withdrawalsRoot")