diff --git a/src/draft/steps/implement_spec/__init__.py b/src/draft/steps/implement_spec/__init__.py
index fb8912a..3de89e0 100644
--- a/src/draft/steps/implement_spec/__init__.py
+++ b/src/draft/steps/implement_spec/__init__.py
@@ -151,6 +151,7 @@ def _generate_commit_message(
             log_path=log_path,
             step_metrics=step_metrics,
             allowed_tools=["Read", "Bash"],
+            extra_args=["--model", "haiku"],
             timeout=timeout,
         )
         msg = result.final_text.strip()