- Java optimization configuration now only accepts a single-label flag. - Proto toolchains are now used in java_lite_proto_library and java_proto_library rules. - Objective-C rules have been updated with new attributes and flags. - Starlark and Build API improvements include added functions, optimizations, and support for experimental features. - Python rules have been updated with new attributes and flags. - Platforms and toolchains API has seen significant updates to support building with Platforms.