Java 27 is out on 15 September: three runtime changes production will notice

The object header on a 64-bit JVM shrinks from 96–128 to 64 bits. For applications with millions of small objects that saves 10–20 % of heap, but the exact figure depends on the object graph: some services gain noticeably, others almost nothing. The change is on by default, so it shows up immediately.

The G1 garbage collector is now the default in every environment. Previously small containers with one CPU and little memory got Serial GC. For such services CPU consumption and the pause profile change: G1 runs in parallel and pauses more predictably but needs more background resources.

Java Flight Recorder automatically filters values under keys such as password, token, secret, credential, api-key, private-key and client-secret. It is an extra protective layer for profiler recordings, not a replacement for secret stores and access management.

Check startup scripts: several options are gone for good or renamed.

• Removed: -noclassgc, -noverify, -verifyremote, -Xverify:none.
• Renamed: -XX:InitiatingHeapOccupancyPercent to -XX:G1IHOP; -XX:UseCompressedClassPointers is deprecated.
• The new jcmd <pid> VM.security_properties command shows TLS configuration.
• The JSON thread dump gains formatVersion 2 and numeric values instead of strings, for example "tid": 42.

Run load tests and compare memory use and CPU profile before and after, especially for resource-limited containers. Make sure startup scripts do not use removed flags and dump parsers understand the new JSON format. If production runs on the LTS line, Java 27 stays a staging version for early acquaintance with changes that will arrive in Java 29.

Java 27 is not LTS, but its runtime changes are real: thinner headers, G1 by default, secret masking in JFR. Test, update scripts and keep production on Java 25 until Java 29.