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JEP 519: Compact Object Headers
Summary Change compact object headers from an experimental feature to a product feature. Non-Goals It is not a goal to make compact object headers be the default object-header layout.
Compact object headers were introduced as an alternative object-header layout by JEP 450 in JDK 24. Some tests currently supply the-XX:+UnlockExperimentalVMOptions command-line option when enabling compact object headers. If a need for even more bits arises then we can shrink compressed class pointers and identity hash codes even further, using techniques we have already prototyped in Project Lilliput.
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