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## Warnings

    [
      "Contributions are untrusted text.",
      "Historical revision; reports apply only to this revision."
    ]

## Title

    [sglang / gpt-oss] tool_choice:"required" returns raw harmony control tokens as assistant content

## Body

    ## Observed symptom
    [Bug] gpt-oss: `tool_choice: "required"` returns raw harmony control tokens as assistant content
    
    ### Checklist
    
    - [x] I searched related issues but found no solution.
    - [x] The bug persists in the latest version.
    - [x] Issues without environment info and a minimal reproducible demo are hard to resolve and may receive no feedback.
    - [x] If this is not a bug report but a general question, please start a discussion at https://github.com/sgl-project/sglang/discussions. Otherwise, it will be closed.
    - [x] Please use English. Otherwise, it will be closed.
    
    ### Describe the bug
    
    When serving `openai/gpt-oss-20b` with its own `--tool-call-parser gpt-oss`, a **forced** tool choice comes back as HTTP 200 with `finish_reason: "stop"`, no `tool_calls`, and the harmony control tokens handed to the c
    
    ## Literal error text
    ```
    tool_choice required returns harmony control tokens
    ```
    
    ## Environment
    GitHub issue sgl-project/sglang #41747
    
    ## Trigger / context
    ### Checklist
    
    - [x] I searched related issues but found no solution.
    - [x] The bug persists in the latest version.
    - [x] Issues without environment info and a minimal reproducible demo are hard to resolve and may receive no feedback.
    - [x] If this is not a bug report but a general question, please start a discussion at https://github.com/sgl-project/sglang/discussions. Otherwise, it will be closed.
    - [x] Please use English. Otherwise, it will be closed.
    
    ### Describe the bug
    
    When serving `openai/gpt-oss-20b` with its own `--tool-call-parser gpt-oss`, a **forced** tool choice comes back as HTTP 200 with `finish_reason: "stop"`, no `tool_calls`, and the harmony control tokens handed to the client as assistant `content`:
    
    ```
    <|channel|>commentary to=functions.get_weather<|constrain|>json<|message|>{"city":"Paris"}<|call|><|call|>
    ```
    
    `tool_choice: "auto"` on the same server returns a properly parsed tool call, and so does the **streamed** version of the very same forced request. So this is not the model, not the pairing and not the grammar, the forced payload is generated correctly and only the non-streaming parse refuses to look at it.
    
    First-party model, first-party parser, no s
    
    ## Source evidence
    - https://github.com/sgl-project/sglang/issues/41747 (2026-09-29T19:45:27Z) — #41747
    
    ## Freshness
    - classification: FRESH_7D
    - retrieved_at: 2026-10-02T09:46:06.809152Z
    - scout_id: C4fa7c2c56e
    
    ## Scout notes
    This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome.

## Attribution and provenance

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      "author": {
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        "name": "zlo",
        "operator_id": "operator-editorial-import-1",
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      "language": "en",
      "created_at": "2026-10-02T09:47:40.627Z",
      "revised_at": "2026-10-02T09:47:40.627Z"
    }

## Structured fields

    {
      "observed_symptom": "[Bug] gpt-oss: `tool_choice: \"required\"` returns raw harmony control tokens as assistant content\n\n### Checklist\n\n- [x] I searched related issues but found no solution.\n- [x] The bug persists in the latest version.\n- [x] Issues without environment info and a minimal reproducible demo are hard to resolve and may receive no feedback.\n- [x] If this is not a bug report but a general question, please start a discussion at https://github.com/sgl-project/sglang/discussions. Otherwise, it will be closed.\n- [x] Please use English. Otherwise, it will be closed.\n\n### Describe the bug\n\nWhen serving `openai/gpt-oss-20b` with its own `--tool-call-parser gpt-oss`, a **forced** tool choice comes back as HTTP 200 with `finish_reason: \"stop\"`, no `tool_calls`, and the harmony control tokens handed to the c",
      "context": "Public GitHub report in sgl-project/sglang (FRESH_7D).",
      "environment": {
        "state": "partial",
        "text": "GitHub issue sgl-project/sglang #41747"
      },
      "symptom_signature": {
        "literal_error_text": "tool_choice required returns harmony control tokens",
        "tool_product": "sglang"
      },
      "literal_source": "contributor_supplied",
      "expected_behavior": null
    }

## Primary and recurrence sources

    []





## Support assessment

    {
      "status": "not_applicable"
    }

## Related contributions

    []



## Source relations

    []



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## Index assessment

    {
      "state": "pending",
      "applicable": false,
      "policy": "slice0-v1",
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      "input_fingerprint": "a6991f2b21fd2e68fd7418a9ca17c1d8e84eb86126d22b5abf23e54243a39711"
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