fix: Support response_format parameter in completion -> responses bridge #16844
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Fixes BerriAI#16810 ## Problem When using completion() with models that have mode: "responses" (like o3-pro, gpt-5-codex), the response_format parameter with JSON schemas was being ignored or incorrectly handled, causing: - Large schemas (>512 chars) to fail with "metadata.schema_dict_json: string too long" error - Structured outputs to be silently dropped - Users' code to break unexpectedly ## Root Cause The completion -> responses bridge in litellm/completion_extras/litellm_responses_transformation/transformation.py was missing the conversion of response_format (Chat Completion format) to text.format (Responses API format). The inverse bridge (responses -> completion) already had this conversion implemented in commit 29f0ed2, but the completion -> responses direction was incomplete. ## Solution Added _transform_response_format_to_text_format() method that converts: - response_format with json_schema → text.format with json_schema - response_format with json_object → text.format with json_object - response_format with text → text.format with text Updated transform_request() to detect and convert response_format parameter before sending to litellm.responses(). ## Changes - Added _transform_response_format_to_text_format() method (lines 592-647) - Modified transform_request() to handle response_format (lines 199-203) - Added comprehensive tests to validate the conversion ## Testing - 5 new unit tests covering all conversion scenarios - Real API test with OpenAI confirming large schemas (>512 chars) work - No more metadata.schema_dict_json errors ## Impact Users can now use completion() with models that have mode: "responses" and: - Use large JSON schemas without hitting metadata 512 char limit - Get proper structured outputs - Have their existing code continue working
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This was referenced Nov 21, 2025
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Title
fix: Support response_format parameter in completion → responses bridge
Relevant issues
Fixes #16810
Pre-Submission checklist
Please complete all items before asking a LiteLLM maintainer to review your PR
tests/litellm/directory, Adding at least 1 test is a hardrequirement - see details
make test-unitType
🐛 Bug Fix
Changes
Summary
When using
completion()with models that havemode: "responses"(likeo3-pro,gpt-5-codex), theresponse_formatparameter with JSON schemas was being incorrectly handled, so :"Invalid 'metadata.schema_dict_json': string too long. Expected maximum 512, but got 1203"Details
The
completion→responsesbridge inlitellm/completion_extras/litellm_responses_transformation/transformation.pywas missing the conversion of:response_format(Chat Completion API format)text.format(Responses API format)The inverse bridge (
responses→completion) already had this conversion implemented in commit 29f0ed2, but thecompletion→responsesdirection was incomplete.Solution
Added
_transform_response_format_to_text_format()method that converts:response_formatwithjson_schema→text.formatwithjson_schemaresponse_formatwithjson_object→text.formatwithjson_objectresponse_formatwithtext→text.formatwithtextUpdated
transform_request()to convertresponse_formatparameter before sending tolitellm.responses().Files Changed
Modified:
litellm/completion_extras/litellm_responses_transformation/transformation.py_transform_response_format_to_text_format()method (lines 592-647)transform_request()to handleresponse_format(lines 199-203)Added:
tests/test_litellm/completion_extras/test_litellm_responses_transformation_transformation.pyTesting ✅