Java 27 reaches general availability with G1 as the default collector in all environments and compact object headers on by default

Sources: primary, release page, discussion
Summary: Mark Reinhold announced JDK 27, the reference implementation of Java 27, as Generally Available on 2026-09-15, stating that build 35 shipped as the second release candidate on 2026-08-20, that no P1 bugs have been reported since, and that build 35 is therefore the GA build. GPL-licensed OpenJDK builds are at jdk.java.net/27. The release carries nine JEPs: 523 makes G1 the default garbage collector in all environments, 534 turns on compact object headers by default, 527 adds post-quantum hybrid key exchange for TLS 1.3, 536 adds JFR in-process data redaction, and the remaining five are previews or incubators, namely 531 lazy constants, 532 primitive types in patterns, 533 structured concurrency, 537 the Vector API and 538 PEM encodings of cryptographic objects.
Why it matters: Two of the nine JEPs change runtime behaviour with no code change on the upgrading side, so collector choice and heap footprint move on upgrade rather than on opt-in.
Follow-up: Track reports of heap footprint and pause-time changes from deployments that were not previously running G1.