Harness profile

Pydantic AI Harness

Open sourcePythonn/a (library) GitHub stars (Aug 2026)

MakerPydantic

LicenseOpen source

StackPython

ModelsAny Pydantic AI supports

Runs whereInside your own Python service

Behavior changed byTyped Python capabilities (50+ listed as of Aug 2026)

Durable memoryComposable capabilities

Drives other agentsNo

Best for

Adding harness behavior to a Python service that already exists. v2.0.0 (Jun 2026) was a breaking release built around "harness-first design with capabilities as a core primitive".

Main weakness

Behavior changes require people who can deploy Python, and the v1-to-v2 break shows what trusting a stability promise costs.

Official docs / repo · Not sure? Run the chooser

Profile facts from the winder.ai comparison of nine agent harnesses (table checked Aug 19, 2026; DeepSeek Harness star count updated Sep 25, 2026 from the live GitHub repo) and vendor documentation. If something here is stale, the vendor page wins - tell us via the kit signup and we will fix it.