Java 27 Arrives With Compact Object Headers, Quantum-Safe TLS, and G1 as Sole Default GC

Java 27 was released in September 2026 as a non-LTS version, meaning most production teams are expected to remain on Java 25 LTS. A notable change is that G1 is now the only default garbage collector, replacing the previous behaviour where constrained environments could silently fall back to Serial GC. Object headers have been reduced from 96 bits to 64 bits by default, offering measurable heap savings that vary depending on object size and memory alignment. TLS 1.3 now automatically negotiates a hybrid quantum-resistant key exchange using ML-KEM alongside classical ECDHE, requiring no code changes from developers. Additional features including Pattern Matching for primitives, Structured Concurrency, and the Vector API advanced further as previews or incubator releases this cycle.
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