Pydantic AI Updates: May 21, 2026

1. Pydantic AI v2.0.0b1 lands harness-first design with capabilities as a single composable primitive

Pydantic AI. Pydantic AI cut v2.0.0b1, the first beta of the V2 line, anchored on a harness-first design that consolidates much of what previously sprawled across Agent arguments into a single primitive: a capability, defined as “a single, composable unit that bundles an agent’s tools, lifecycle hooks, instructions, and model settings.” Extensions — memory systems, guardrails, toolkits — are all expected to flow through capabilities=[...] rather than scattered configuration, with built-in, Pydantic AI Harness first-party, and third-party capabilities sharing one interface. Breaking changes include fewer default provider extras (Bedrock, Groq, Mistral now require explicit installation), OpenAI model names defaulting to the Responses API (use openai-chat: prefix for Chat Completions), web tools defaulting to native-only execution, default instrumentation upgraded to v5, and function tools executing alongside successful outputs; the stable V2.0 is expected within roughly two weeks. Source

2. Pydantic AI v1.100.0 ships the V2 migration release with native Bedrock JSON and an IPv6 URL fix

Pydantic AI. v1.100.0 lands as the recommended pre-V2 upgrade, pairing a security fix that normalizes IPv6 transition forms in URL validation with native Bedrock JSON output, strict tool-call support on Bedrock, and a batch of deprecations that prepare the codebase for the V2 surface, including changes to Gateway API usage, evals, and streaming. The release exists primarily to let teams clear deprecation warnings before flipping to v2.0.0b1, and the project guidance is to step through v1.100.0 first rather than upgrading directly from earlier 1.x releases. The double-release timing on the same day mirrors the pattern Pydantic has used for prior major-version cutovers and gives existing 1.x users a documented escape hatch as the V2 beta ramps. Source