Pydantic AI Updates: September 27, 2026

1. Pydantic AI Harness Adds Hosted MCP Tools for 11 Services in Two Releases

Pydantic AI. The pydantic-ai-harness v0.35.0 release added hosted MCP tool integrations for Logfire, GitHub, Linear, Notion, Google Workspace, Slack, and Ordinal. Later the same day, v0.36.0 added Grain, DayAI, PostHog, and Pylon. v0.35.0 also composes ACP sessions from capabilities instead of extracted toolsets and files internal agent runs under the parent run’s conversation. Source

2. Harness v0.36.0 Sizes Compaction From the Model’s Context Window

Pydantic AI. In pydantic-ai-harness v0.36.0, the compaction window is now read from Model.context_window rather than configured separately, and the harness asks for a summarizer model when a run produces no text. The Coder capability now delegates to the agent it is bound to through SubAgents(include_self=True). The release also requires pydantic-monty>=1 and adds WebSocket support. Source