This Annex to the Java SE 15 Specification contains the Java SE 15 version of the Java Object Serialization Specification. It is unchanged from the Java SE 14 and Java SE 13 versions.
The Java SE 15 Platform includes one preview feature whose specification changes the Serialization Spec:
The changes to the Serialization Specification are incorporated into the Java SE Platform Specification by reference, and made a part thereof, if and only if preview features are enabled at run time. If preview features are not enabled at run time, then the Java SE 15 version of the Serialization Specification is incorporated instead.