It's been a while since the last Intel X.Org driver update, but xf86-video-intel 2.21.7 is now out there. This driver adds in all known Haswell PCI IDs plus now correctly identifies the top-end Haswell GT3 graphics variant.
Other non-Haswell work in this Intel 2.21.7 DDX include assertion failures, an XvMC fix, an Ironlake bug-fix, a change to prevent using old frame-buffers after resizing, a compilation fix, improvements to partial migration of render sources, and support for copy-on-write support for cloning pixmaps. The new copy-on-write support for cloning pixmaps should provide some benefits right away for Mozilla Firefox users.
More details on the xf86-video-intel 2.21.7 driver changes can be found via this Git commit.