This is the first release candidate for modules/apps/callbacks v10.0.0.
The main changes are noted in ibc-go's release notes: https://github.com/cosmos/ibc-go/releases/tag/v10.0.0-rc.1
Special notice for the callbacks middleware release are:
IBC v2 support
The callbacks middleware can be wired up with the new IBC v2 transfer IBC Application.
More information about IBC v2 middleware can be found in the ibc-go release notes.
It is worth noting that CosmWasm itself does not have native IBC v2 support yet (planned in an upcoming release), but can still be used for callbacks for both IBC v1 and IBC v2.