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ChatAnthropic.Bind_tools() Fails On Anthropic Browser_toolset_20260801 And Drops Toolset_name Metadata

ChatAnthropic incorrectly routes the documented browser_toolset_20260801 client toolset through JSON-schema conversion, raising ValueError. Non-null toolset_name on tool_use blocks is lost in multi-turn requests, and ordinary tool calls expose toolset_name=None.

highConfidence 89%Langchain-Anthropic Affected Vlangchain-Anthropic==1.7.2 Affected Vlangchain-Core==1.6.4 Affected Vanthropic==1.1.0 Fixed Vlangchain-Anthropic>=1.7.3

Origin Analysis

The _BUILTIN_TOOL_PREFIXES tuple lacks 'browser_toolset_', so _is_builtin_tool() returns False and bind_tools treats the client toolset as a conventional tool/JSON schema. Additionally, _format_output() retains toolset_name=None for all tool_use blocks instead of omitting it, and _format_messages()/ToolMessage conversion do not propagate non-null toolset_name from AIMessage.content to Anthropic tool_use/tool_result blocks.

1. Instantiate ChatAnthropic(model='claude-sonnet-4-5-20250929').\n2. Call model.bind_tools([{'type':'browser_toolset_20260801','configs':{'javascript_exec':{'enabled':True}}}])\n3. Observe ValueError: Unsupported function.\n4. Send a multi-turn request with an AIMessage containing a tool_use block with toolset_name='computer' and a paired ToolMessage.\n5. Inspect request payload to see toolset_name missing and tool_result lacking toolset_name.\n6. Run a plain tool call through _format_output and observe toolset_name: None.

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 patch relies on anthropic SDK >= version that includes toolset_name on ToolUseBlock (likely 1.0+). If older SDK lacks toolset_name, getattr returns None and behavior is unchanged, but toolset feature won't work; ensure anthropic>=1.1.0. The browser_toolset_ prefix may cause any custom tool definition whose name starts with browser_toolset_ to bypass normal conversion—this is intended for client toolsets but could mask malformed regular tools in that namespace. The reverse search stops at HumanMessage, but if a tool_call_id is reused across multiple tool results in the same assistant turn, the first match from the end is used; that is usually correct because each tool_use id should be unique per turn. Concurrency/streaming: _format_output is per response and thread-safe; _format_messages is per request and no shared mutable state. Rollback: remove browser_toolset_ from _BUILTIN_TOOL_PREFIXES and revert _format_output/_format_messages tool_use/tool_result dict construction to previous versions. Test with computer_toolset_20260801, browser_toolset_20260801, ordinary tool with no toolset_name, and multi-turn toolset where tool_result echoes toolset_name.