Pydantic AI Updates: April 26, 2026

1. Pydantic AI v1.87.0 Adds Deferred Tool Calls, Event-Stream Processing, and GPT-5.5 Thinking

Pydantic AI. v1.87.0 introduces a HandleDeferredToolCalls capability with a corresponding handle_deferred_tool_calls hook, letting agents schedule and resume tool execution out-of-band rather than blocking the main loop — useful for human-in-the-loop steps or tools that must complete asynchronously. A new ProcessEventStream capability formalizes a hook for transforming the model’s event stream as it arrives, and the release adds explicit handling for the GPT-5.5 thinking settings introduced with OpenAI’s recent launch so the framework can plumb them through without ad-hoc patching. The two new capabilities are the more interesting change: they push Pydantic AI further toward an agent runtime where planning, deferral, and event-stream interception are first-class extension points rather than implementation-private behavior. Source