Exchange 2010 SP3 is finally out and people have been waiting for it to be able to upgrade to Exchange 2013, but hurry slowly, Microsoft at the same time announce that to get coexistence with Exchange 2010, you not only need Exchange 2010 SP3 but also Exchange 2013 CU1
As usual you need to update Active Directory schema before applying SP3. See the Exchange 2010 SP3 release notes.
If the Exchange 2013 CU1 will need to extend the schema once more, only time can tell.
Hopefully we don’t need to see a version 2 of these patches or any new bugs introduced like we sort of have been used to the last year, sigh.