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ChatAnthropic Sends Unsupported Tool Choice And Disabled Thinking For Claude Opus 5.5

ChatAnthropic allows forced tool_choice and thinking={"type":"disabled"} to reach the Anthropic API for claude-opus-5-5, causing 400 invalid-request errors. bind_tools(), call-time kwargs, model_kwargs, and create_agent() with structured-output tools are affected.

highConfidence 90%Langchain-Anthropic Affected V1.7.3

Origin Analysis

_supports_forced_tool_choice() is not consulted in bind_tools() or final _get_request_payload(), so forced tool_choice is sent to Opus 5.5. In addition, Opus 5.5-specific thinking validation is missing; only Opus 5 xhigh/max disabled-thinking is rejected.

1. Instantiate ChatAnthropic(model="claude-opus-5-5"). 2. Call bind_tools([GetWeather], tool_choice="any") and inspect _get_request_payload(...)["tool_choice"]; it returns {"type":"any"} instead of auto. 3. Instantiate ChatAnthropic(model="claude-opus-5-5", thinking={"type":"disabled"}) and inspect _get_request_payload("Hello")["thinking"]; it returns {"type":"disabled"} with no ValueError. 4. Send either payload to Anthropic API and observe 400 invalid-request.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Downgrading forced tool_choice to auto changes behavior: the model may not invoke the tool, so callers must handle missing tool calls. The warning is the only signal; upgrade path should ensure downstream logic tolerates auto choice. The monkey patch modifies _get_request_payload; if future versions add new parameters they must be preserved. Rollback: revert this monkey patch or remove forced tool_choice/avoid disabled thinking for Opus 5.5.