feat(telemetry): emit gen_ai.response.model from Output.metadata["model"]

src/celeste/telemetry.py

@@ -224,6 +224,7 @@ def output_attributes(output: Output[Any]) -> dict[str, Any]:
         attrs[semconv_key or f"celeste.usage.{field_name}"] = value
     if output.finish_reason is not None and output.finish_reason.reason is not None:
         attrs["gen_ai.response.finish_reasons"] = (output.finish_reason.reason,)
+    attrs["gen_ai.response.model"] = output.metadata["model"]
     return attrs
 
 

tests/unit_tests/_telemetry_helpers.py

@@ -1,7 +1,7 @@
 """Shared fixtures and helpers for telemetry-related unit tests."""
 
 from collections.abc import AsyncIterator
-from typing import Any, ClassVar
+from typing import Any, ClassVar, Unpack
 
 from celeste.io import Chunk, Output, Usage
 from celeste.parameters import Parameters
@@ -30,6 +30,19 @@ class TelemetryStream(Stream[TelemetryOutput, Parameters, Chunk]):
     _output_class: ClassVar[type[Output]] = TelemetryOutput
     _empty_content: ClassVar[str] = ""
 
+    def __init__(
+        self,
+        sse_iterator: AsyncIterator[dict[str, Any]],
+        stream_metadata: dict[str, Any] | None = None,
+        **parameters: Unpack[Parameters],
+    ) -> None:
+        """Default `stream_metadata={"model": "test-model"}` to mirror production wiring."""
+        super().__init__(
+            sse_iterator,
+            stream_metadata=stream_metadata or {"model": "test-model"},
+            **parameters,
+        )
+
     def _aggregate_content(self, chunks: list[Chunk]) -> str:
         """Concatenate chunk content."""
         return "".join(chunk.content for chunk in chunks)

tests/unit_tests/test_telemetry_streaming.py

@@ -16,6 +16,7 @@
 from tests.unit_tests._telemetry_helpers import (
     TelemetryOutput,
     TelemetryStream,
+    TelemetryUsage,
     async_iter,
 )
 from tests.unit_tests.conftest import start_test_span
@@ -213,10 +214,24 @@ async def test_total_reasoning_cached_tokens_emitted(
     def test_off_spec_usage_emitted_under_celeste_namespace(self) -> None:
         """Modality-specific Usage fields fall through to `celeste.usage.<field>`."""
         usage = _OffSpecUsage(images_generated=4, audio_seconds=1.5)
-        output: Output[Any] = TelemetryOutput(content="", usage=usage)
+        output: Output[Any] = TelemetryOutput(
+            content="", usage=usage, metadata={"model": "test-model"}
+        )
 
         attrs = telemetry.output_attributes(output)
 
         assert attrs["celeste.usage.images_generated"] == 4
         assert attrs["celeste.usage.audio_seconds"] == 1.5
         assert "gen_ai.usage.images_generated" not in attrs
+
+    def test_response_model_emitted_from_metadata(self) -> None:
+        """`gen_ai.response.model` reads from `output.metadata["model"]`."""
+        output: Output[Any] = TelemetryOutput(
+            content="",
+            usage=TelemetryUsage(),
+            metadata={"model": "claude-opus-4-1-20250805"},
+        )
+
+        attrs = telemetry.output_attributes(output)
+
+        assert attrs["gen_ai.response.model"] == "claude-opus-4-1-20250805"