Even if this is a very old branch, the kernel developers are still releasing updates for it and there is no sign that they intend to stop anytime soon. In fact, this latest iteration is quite a big one, but that was to be expected.
Linux developers are very actively pushing updates to Linux kernel. The latest Linux 3.12.36 brings quite a few changes and some security fixes. This is 36th update of the 3.12 series. Linux developer, Jiri Slaby has published the changelog and press release. This latest iteration is quite a big one.
Development team has pushed LTS version of the Linux kernel, which means you can expect updates for long time. The press release recommends all users of 3.12 series to upgrade to 3.12.36. There is list of latest kernel versions that Linux has recently published. If you are running Linux Kernel 3.12.x branch, you should definitely consider to upgrade to this latest kernel release.
You can find the updated 3.12.y git tree at git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git . A complete list of kernel updates for this branch can be found in official announcement. Linux kernel 3.12.36 LTS is available to download.