diff --git a/src/exo/shared/types/api.py b/src/exo/shared/types/api.py
index 494f02dd..89ec6cdb 100644
--- a/src/exo/shared/types/api.py
+++ b/src/exo/shared/types/api.py
@@ -239,10 +239,12 @@ class ChatCompletionTaskParams(BaseModel):
     tool_choice: str | dict[str, Any] | None = None
     parallel_tool_calls: bool | None = None
     user: str | None = None
+    # Internal flag for benchmark mode - set by API, preserved through serialization
+    bench: bool = False
 
 
 class BenchChatCompletionTaskParams(ChatCompletionTaskParams):
-    pass
+    bench: bool = True
 
 
 class PlaceInstanceParams(BaseModel):
diff --git a/src/exo/worker/engines/mlx/generator/generate.py b/src/exo/worker/engines/mlx/generator/generate.py
index 53b35df4..3e6f9a7a 100644
--- a/src/exo/worker/engines/mlx/generator/generate.py
+++ b/src/exo/worker/engines/mlx/generator/generate.py
@@ -8,7 +8,6 @@ from mlx_lm.sample_utils import make_sampler
 from mlx_lm.tokenizer_utils import TokenizerWrapper
 
 from exo.shared.types.api import (
-    BenchChatCompletionTaskParams,
     ChatCompletionMessage,
     FinishReason,
     GenerationStats,
@@ -368,7 +367,7 @@ def mlx_generate(
 ) -> Generator[GenerationResponse]:
     # Ensure that generation stats only contains peak memory for this generation
     mx.reset_peak_memory()
-    is_bench: bool = isinstance(task, BenchChatCompletionTaskParams)
+    is_bench: bool = task.bench
 
     # Currently we support chat-completion tasks only.
     logger.debug(f"task_params: {task}")