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ChatAnthropic Forwards Deprecated Top_k To Claude Opus 5 Causing HTTP 400

ChatAnthropic in langchain-anthropic 1.6.1 sends top_k=10 to claude-opus-5, which Anthropic has deprecated for Opus 4.7 and later, resulting in a 400 BadRequestError. The client should validate locally and reject unsupported parameters before making a network request.

highConfidence 92%Langchain-Anthropic Affected V1.6.1

Origin Analysis

langchain-anthropic's ChatAnthropic includes top_k in the request payload whenever it is not None, without model-specific validation of deprecated sampling parameters. Anthropic's API rejects non-default values of temperature, top_p, and top_k for Opus 4.7+ models, but the client does not check this before sending.

1. Set ANTHROPIC_API_KEY. 2. Run: ```python import os import anthropic from langchain_anthropic import ChatAnthropic model = 'claude-opus-5' control = ChatAnthropic(model=model, max_tokens=8, max_retries=0) print(control.invoke('Reply with exactly: hi').content) subject = ChatAnthropic(model=model, top_k=10, max_tokens=8, max_retries=0) print(subject.invoke('Reply with exactly: hi').content) ``` 3. Observe: control succeeds; subject raises anthropic.BadRequestError with status 400 and message '`top_k` is deprecated for this model.'

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

This hotfix only addresses top_k; temperature and top_p remain vulnerable to the same deprecation and may still cause 400 errors if users set non-default values. The list of deprecated models is hardcoded and must be updated as Anthropic adds or renames models. Users who previously relied on the client silently forwarding top_k will now get an exception, but this is intended behavior. Rollback: revert this method to the previous version to restore old behavior.