Java 21 introduces the notion of sequenced collections, the Z Garbage Collector (ZGC) has been extended to maintain separate generations for young and old objects for improving Java app performance, virtual threads are now out of preview form, and the Windows 32-bit x86 port has been deprecated for removal.
Java 21 also brings some new preview features including string templates, the latest iteration on the foreign function and memory API, unnamed classes and instance main methods, scoped values, and structured concurrency.
You can find the GPL-licensed OpenJDK builds at the OpenJDK website, and the closed source builds from Oracle are also available.
