Java 27 Grows Up, Makes Better Choices
The Register, Wednesday, September 16th, 2026
JDK 27 turns on good defaults rather than asking developers to opt in, led by 64-bit compact object headers.
JDK 27 is a short-term release with four production-ready JEPs, none of which require immediate changes to developer code.
Compact object headers are now on by default under JEP 534, cutting the traditional 96-bit Java object header to 64 bits; a SPECjbb2015 run found the change produced 22% less heap space and 8% less CPU time, and Amazon already runs hundreds of production services with them while SAP has made them the default in its SapMachine OpenJDK fork.
The new layout still reserves room for future work, including four bits for Project Valhalla. Looking ahead to quantum computing, JEP 527 implements post-quantum hybrid key exchange for TLS 1.3, offering three hybrid options that pair a quantum-resistant algorithm with ephemeral elliptic-curve Diffie-Hellman.