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v1.77.0

pydantic/pydantic-aiv1.77.0Apr 3, 2026by DouweM

AI Summary

The release focuses on expanding tool capabilities with a local `WebFetch` implementation and adding `ThreadExecutor` support, alongside improvements in instruction caching and streaming SDK error handling.

Key Highlights

  • Added local `WebFetch` tool with fallback logic for providers lacking builtin support.
  • Added `defer_loading` to tools to enable lazy initialization.
  • Added `ThreadExecutor` capability and `Agent.using_thread_executor()` method.
  • Implemented smart instruction caching for Anthropic/Bedrock models.
  • Wrapped streaming SDK errors in `ModelHTTPError`/`ModelAPIError`.

New Features

  • Local WebFetch tool
  • `defer_loading` for tools
  • `ThreadExecutor` capability
  • Smart instruction caching

Full Release Notes

<!-- Release notes generated using configuration in .github/release.yml at main -->

## What's Changed
### 🚀 Features
* feat: add local `WebFetch` tool and have `WebFetch` capability use it when provider lacks builtin support by @DEENUU1 in https://github.com/pydantic/pydantic-ai/pull/4906
* Add `defer_loading` to tools and toolsets to enable tool search by @dsfaccini in https://github.com/pydantic/pydantic-ai/pull/4090
* Add `ThreadExecutor` capability and `Agent.using_thread_executor()` by @DouweM in https://github.com/pydantic/pydantic-ai/pull/4942
* feat: smart instruction caching — automatically insert Anthropic/Bedrock cache boundary at static/dynamic split by @Alex-Resch in https://github.com/pydantic/pydantic-ai/pull/4865
* Support `server_message_id` in `VercelAIEventStream` by @dsfaccini in https://github.com/pydantic/pydantic-ai/pull/4579
### 🐛 Bug Fixes
* fix: run output validators for image outputs by @dsfaccini in https://github.com/pydantic/pydantic-ai/pull/4938
* Wrap streaming SDK errors in `ModelHTTPError`/`ModelAPIError` by @dsfaccini in https://github.com/pydantic/pydantic-ai/pull/4889

## New Contributors
* @Alex-Resch made their first contribution in https://github.com/pydantic/pydantic-ai/pull/4865

**Full Changelog**: https://github.com/pydantic/pydantic-ai/compare/v1.76.0...v1.77.0