During the weekend, Treyarch introduced a new patch for the Steam version of the game. This is coming off criticism by a good chunk of users who have the PC version of the game, as the game currently stands at a Mixed rating on Steam reviews, with several of them indicating that the game's performance has issues. I myself did have issues as first eluded to, although since then I've put a GTX 980 in my machine, and obviously have had less issues in question. In particular, frame rate drops were noticeable in several areas of the game, as in Zombies for example, you'd drop a good 10-20 frames when changing over into the Demon form.
While the latest patch includes bug fixes and performance improvements, there isn't a set of release notes in question. Although it should be noted that the Director of Development for Treyarch on twitter seems to be responsive to issues that players are presenting, so any information regarding Call of Duty: Black Ops III should be sent there. However, many users are still seeing problems with the game, ranging from drops to 0 FPS and stuttering when entering a new map, to those in the country of Brazil having problems with servers despite having low ping and seemingly optimal conditions. It seems to have fixed some cases however, as some have indicated that they are now getting performance out of the game with such builds of i7 6700k with a GTX 390 getting 100+ fps. Many of the recommendations provided by the company seem to revolve around resetting your graphics settings to default and trying to see what your performance looks like at that point, even if you end up changing it afterward. From what I understand, certain background variables may be reset to default values that may have been causing some issues regardless.
One thing to note specifically after the patch went live is that there is a known crash on Windows 7 and Nvidia cards if service pack one is not installed. So those who are having issues on that OS should check to see if that is a primary cause of crashing.
Even after putting the new GTX 980 in my machine, I was able to test before and after the latest patch. For me, it does seem to have improved things slightly although I am noticing some issues regarding the game running for a period of time in Zombies mode (in particular, frame rate stutters). While I'm in the game for the zombies mode, it still seems that the game has a bit to go to isolate the specific user problems in question, and Treyarch has indicated they will be doing multiple patches in the next coming weeks in order to get to the bottom of it. I am myself not happy with the performance yet, but it is an improvement over the launch day shenanigans. Also, is that hard to put in actual release notes? As a software developer myself, it infurates me that it's so unspecific about the changes.