[meghana-madhyastha]

Ask the configured reasoning parser instead, so structured outputs aren't enforced inside for models that always reason.

Purpose

OpenAIServingChat forces reasoning_ended=True for the structured-output gate whenever include_reasoning=False, treating "the client doesn't want to see reasoning" as "the model won't produce reasoning". For models whose chat template always opens the assistant turn with <think> (e.g. zai-org/GLM-5.3-Flash) the block is still generated, so a json_schema response format or strict-tool grammar is enforced from the first token, inside the reasoning. Result: ~30 completion tokens, empty content, reasoning_tokens=0. OpenRouter's reasoning.exclude maps to exactly this request shape, so it shows up as broken structured output there.

This PR lets the configured reasoning parser decide (is_reasoning_end(prompt_token_ids)) and keeps the include_reasoning shortcut only for servers with no reasoning parser. The check keys on the server-level reasoning-parser setting rather than parser.reasoning_parser, because when tool and reasoning parsing share one parser engine, ParserManager.get_parser returns the engine class itself and that attribute is None. Note: this change was developed with AI assistance (Claude); the code and tests were reviewed and validated end-to-end by the author.

Test Plan

Unit test added: tests/entrypoints/openai/chat_completion/test_reasoning_gate.py — asserts the reasoning_ended value passed to engine.generate with an engine-style parser (no reasoning_parser attribute) for hidden and visible reasoning, and the legacy shortcut when no reasoning parser is configured.

Test Result

Before: finish_reason=stop, completion_tokens=25, content=null, reasoning_tokens=0.
After: completion_tokens=159, reasoning_tokens=129 (hidden), content='{"location": "London", "temperature": 14, "conditions": "Partly cloudy"}'.

Same request with include_reasoning: true is unchanged before/after. The three new unit tests pass; an internal endpoint eval suite (reasoning / structured output / tool calling / vision) went from 90/94 to 94/94 with this change on the model above.

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• [ x] The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @meghana-madhyastha.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork