Pydantic v3 shipped in late 2025. It has a new Rust-backed core and a fresh model system. With FastAPI 0.115+, you get auto request checks, fast JSON output, and OpenAPI 3.1 docs. No manual schema work. Data errors get caught at the API edge. Client SDKs come from the live spec. The check overhead that used to be a bottleneck is now mostly gone.
This guide walks through what changed in v3, how to lay out a production project, the validation patterns to know, and what deployment looks like when you care about speed.






