diff --git a/miles/rollout/generate_hub/agentic_tool_call.py b/miles/rollout/generate_hub/agentic_tool_call.py
index feba568164..89e0bf7fc4 100644
--- a/miles/rollout/generate_hub/agentic_tool_call.py
+++ b/miles/rollout/generate_hub/agentic_tool_call.py
@@ -59,6 +59,7 @@ async def generate(input: GenerateFnInput) -> GenerateFnOutput:
     max_seq_len = getattr(input.args, "max_seq_len", None)
 
     metadata = input.sample.metadata
+    metadata = {**metadata, "sample_idx": input.sample.index}
     if max_seq_len is not None:
         metadata = {**metadata, "max_seq_len": max_seq_len}
     if tracer.session_server_instance_id: