This is a large release, containing several new major features

(such as rollup.js and TypeScript support, Server-Sent Events, and a

Health Check view, and pyest support for extensions), improved Python

type hints, modern package-related infrastructure, bug fixes, and

performance optimizations.

Built the release notes. Checked for build errors, bad links, and

spelling errors.
Went through every commit since 4.0 Beta 3 and verified they were

all included.