X.Org Server 1.13 was released in early September but it took over three months for AMD to officially support the xorg-server release by Catalyst. This driver release happened on the same day as NVIDIA's 313.18 Linux driver, which already brought forth support for the unreleased X.Org Server 1.14.
Aside from official X.Org Server 1.13 support, the only other official new feature of AMD Catalyst 13.1 is "production support" for Ubuntu 12.10. But at least there's also a couple of resolved bugs, per the AMD release notes.
The Catalyst 13.1 driver release for Linux x86/x86_64 can be downloaded from AMD.com.