Oracle has released Java 27, making the Garbage-First (G1) garbage collector the default across all environments. This change follows improvements to G1’s performance, bringing it to parity with the Serial collector in terms of throughput, latency, memory footprint, and start-up time.
Since JDK 9, G1 was the default garbage collector for Java server environments. According to JEP 523, testing now demonstrates G1 is competitive with Serial across all heap sizes. Oracle states that recent work, including JEP 522 to reduce synchronization, has brought G1’s maximum throughput close to that of Serial. G1’s latency has consistently been better due to incremental garbage collection of the old generation, and native memory usage has been reduced to comparable levels.
OpenJDK / Java 27 also introduces support for Post-Quantum Hybrid Key Exchange for TLS 1.3, the newest preview of lazy constants, the seventh preview of structured concurrency support, and compact object headers by default. The shift to compact object headers, proven stable since JDK 24, reduces object headers from 96 bits to 64 bits, improving deployment density, data locality, and reducing heap size. Additionally, the latest incubator version of Java’s Vector API is included.
JEP 523 states, “G1’s performance is now sufficient to replace Serial in all situations in which the JVM would previously have selected Serial. It is time to stop selecting Serial by default.”
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