Add a functional programming API for agents and direct model requests, leveraging signatures for improved usability and design considerations.
### Description # Feature Request: Signature-Based Functional API for Pydantic AI As an upfront note, I'm an avid user of Pydantic AI and spent about 6 hours iterating with Gemini 3.1 and Opus 4.6 on this feature request + a couple of proofs-of-concept (PoC) scripts to flesh out the behavior/catch important design considerations. Hopefully between the descriptions and the PoCs, it should be straightforward to implement/integrate once the final edge cases are fleshed out. ## Executive Summary This proposal introduces a first-class **Functional API** for Pydantic AI, enabling developers to define agents and model requests using native Python functions and decorators. By leveraging function signatures for tool extraction, dependency injection, and recursive orchestration, this API provides a developer experience (DX) similar to FastAPI or FastMCP. This feature request is to bridge the gap between Pydantic AI Agents and directly using a client SDK such as `openai` while providing backen