Overview
- JEP 522 redesigns G1 with a dual card table that delivers roughly 5–15% throughput gains on reference-heavy workloads, with no configuration required.
- The JDK HttpClient now speaks HTTP/3 over QUIC via JEP 517 and falls back to HTTP/2, benefiting RestClient users while WebClient on Reactor Netty follows its own timeline.
- JEP 500 begins warning on reflective mutation of final fields, with likely hits in libraries such as Hibernate, Mockito, and Lombok, and runtime flags available to deny or temporarily allow the behavior.
- A new UUID.version7() API provides time-ordered identifiers that can reduce database index fragmentation compared with random UUIDv4.
- Because Java 26 is a non-LTS release with six months of Premier support, guidance is to keep production on Java 25 LTS as Spring Boot 4.0.x officially supports up to 25 and to add 26 to CI to catch compatibility issues.