Microsoft has released Exchange 2010 SP3 today and co-existence support for 2013 is included, however in a last minute announcement you will need to use Exchange 2013 CU1 (that's Cumulative Update 1) media to do the install. CU1 is also scheduled for release in Q1 2013l
Also supported is installing Exchange 2010 on a Windows Server 2012 platform, installing the management tools on Windows 8 and although it was possible before this update running 2010 in a forest at Server 2012 Functional level is also supported. Installation will need to be done from the SP3 media and as with previous versions you cannot upgrade the server OS while Exchange us installed.
As with any previous Exchange service pack I would strongly recommend installing this update in your test lab and keep an eye on the TechNet forums for any issues that others have discovered.
Direct link to the download: Exchange 2010 SP3
Take a look at what's new in SP3 and the all-important release notes, especially if you are upgrading from 2010 RTM: What's New and Release Notes