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fix(proxy): send a forced tool_choice in the Responses shape - #212
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GoDiao merged 2 commits intoOct 30, 2026
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anthropicToOpenaiResponses reused the Chat Completions form
{type:'function', function:{name}} for tool_choice type=tool. The Responses API
takes the flat {type:'function', name}, so a forced tool from an Anthropic client
was rejected with a 400.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
# Conflicts: # CHANGELOG.md
GoDiao
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Thanks @pcbeingused333, nice find! We checked it against OpenRouter's Responses API with one request that differs only in tool_choice: the nested { type: 'function', function: { name } } that main sent gets a 400 (invalid_prompt), and the flat { type: 'function', name } from this PR succeeds and the model calls the tool.
We pushed a merge of main to resolve the CHANGELOG conflict. Your entry had landed in the 0.6.1 section, so we moved it under [Unreleased] and added a thanks line. Approving and merging. Thanks again!
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When a client sends an Anthropic request with a forced tool (
tool_choice: { type: 'tool', name }) through a provider that uses the OpenAI Responses API,anthropicToOpenaiResponsesconverted it with the Chat Completions form,{ type: 'function', function: { name } }. The Responses API takes the flat form{ type: 'function', name }, so the upstream rejected the request with a 400.The Responses converter now returns
{ type: 'function', name };any,autoandnonekeep mapping torequired,autoandnone, and the Chat Completions converter is unchanged (its nested form is the correct one there).The flat shape matches what this repo already assumes elsewhere for the same API:
OpenAIResponsesRequest.toolsintransform/types.tscarries{ type: 'function', name, description, parameters }, with the name at the top level, whileOpenAIToolfor Chat Completions keeps it underfunction.Tests in
proxy-transform.test.ts: the forced-tool shape (fails on the previous code) and the three string mappings.bun test src/server/__tests__/proxy-transform.test.ts: 42 pass. Not run against a live Responses upstream. CHANGELOG line under Unreleased.This change was made with Claude Code.