On the same afternoon, the React team cut four patch releases at once — 19.3.1, 19.2.9, 19.1.10, and 19.0.9 — spanning every maintained 19.x line back to 19.0. Each ships exactly one change: an improvement to the React Server Components transport protocol. No API changes, no migration, nothing to read twice. If you're on any 19.x line and use RSC, take the patch for your branch on the next routine bump.