This proposal updates system parachains to v9381. The main change from v9370 is the introduction of XCM v3. Note that this is "v9381" instead of "v9380" due to late changes in the release process after the Westend parachains had already been upgraded to v9380.
This proposal also tells the Relay Chain to communicate with system parachains using XCM v3 in the future. It is scheduled for 600 blocks after the upgrade authorization to coincide with the actual upgrades.
Release notes are in the Cumulus repo.