feat: Add ToolSearchTool and defer_loading for dynamic tool discovery #3620
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Adds support for dynamic tool discovery without loading all tool definitions upfront, reducing token usage for agents with many tools. - Add `ToolSearchTool` builtin tool for on-demand tool discovery - Supports `search_type` of 'regex' or 'bm25' (defaults to None = provider's default) - Add `defer_loading` field to `ToolDefinition` and `Tool` class - Automatically add `ToolSearchTool` when any tool has `defer_loading=True` - Update Anthropic model to map `defer_loading` to API - Enable `advanced-tool-use-2025-11-20` beta automatically Supported by Anthropic models. See https://docs.anthropic.com/en/docs/agents-and-tools/tool-use/tool-search-tool 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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This was referenced Dec 8, 2025
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Thanks for working on this @ryx2! I was just talking to @t0yv0 who is going to work on adding support for this feature to Pydantic AI itself (#3590), so that it works for all models while using the provider-native functionality when available. See details on what that will look like at #3666 (comment). He's going to use this PR as a starting point for the Anthropic side of things, so once he submits his extended PR I expect to close this one. |
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Summary
Adds support for dynamic tool discovery without loading all tool definitions upfront, reducing token usage for agents with many tools.
ToolSearchToolbuiltin tool for on-demand tool discoverysearch_typeof 'regex' or 'bm25' (defaults toNone= provider's default)defer_loadingfield toToolDefinitionandToolclassToolSearchToolwhen any tool hasdefer_loading=Truedefer_loadingto APIadvanced-tool-use-2025-11-20beta automatically when features are usedSupported by Anthropic models.
See https://docs.anthropic.com/en/docs/agents-and-tools/tool-use/tool-search-tool
Test plan
tests/models/anthropic/test_tool_search.pyRelated
Split from #3550 per @DouweM's recommendation to separate the features into individual PRs.
🤖 Generated with Claude Code