The release notes should be up on that page tomorrow, but in the meantime:
- Added experimental libusb support to linux/mac adb
To use the libusb backend, set the environment variable ADB_LIBUSB=1
before launching adb server. The new `adb host-features` command will
tell you whether or not you're using libusb. In this release, the old
non-libusb implementation remains the default.