Fastify 5.11.2

Fastify 5.11.2 shipped on August 3, 2026 — and so did 5.11.1, roughly ten minutes earlier, the same morning. Two patches in one day is usually a sign that the first one didn't quite land, so let's not get carried away.

The One That Matters

The interesting change is #6889: Fastify will no longer force-close in-flight connections when the server goes idle. On paper that reads like a pure win — requests that are mid-flight when the event loop quiets down get to finish instead of being cut off. In practice, it changes the timing of when sockets are torn down, and if you run long-lived connections or heartbeat-style keep-alives, the connection lifecycle you tuned against 5.11.0 just moved.

Worth a look in staging before you trust it in production.

Quieter Fixes

There's a new warning when you override the HTTP method (#6879) — helpful, until your logs fill with it because some proxy middleware has been doing exactly that for years. The type fix (#6888) finally lets you pass an explicit http2: false in server options without TypeScript complaining, which is nice, but it's a types-only change: your runtime behavior is unchanged.

There's also a documentation clarification that attachValidation exposes the parsed body on request.validationError, which is genuinely useful if you've ever grepped the docs for that.

The Verdict

Six commits between 5.11.0 and 5.11.2, four of them meaningful. It's a safe patch release for most apps — but the idle-connection change is exactly the kind of thing that only breaks people who weren't testing for it. Upgrade, run your soak tests, and pay attention to your socket metrics afterward.