Spring Boot 4.0.9 lands with 99 fixes, nine months into the 4.0 line

Victoria Shinder26 October 2026, 14:481 min read

Spring Boot 4.0.9 is out on Maven Central, a maintenance release that bundles 99 bug fixes along with documentation improvements and dependency upgrades. There are no new features and nothing to migrate; it is the kind of point release a team on the 4.0 line should take without ceremony.

What it means

Ninety-nine fixes in a single patch release is the number worth sitting with. On a mature line that figure would raise an eyebrow; on 4.0, still early in its life, it is the expected shape — the long tail of edge cases that only surfaces once a major version meets real applications, caught and closed on a steady cadence. The practical reading for anyone pinning a Spring Boot version: 4.0.x is being tended actively, and staying one patch behind buys nothing. Upgrades inside a patch line carry no API risk by definition, so the cost of taking this is a dependency bump and a test run. The cost of skipping it is carrying bugs someone already fixed.