Source: http://forum.worldoftanks.com/index.php?/topic/352479-901-update-coming/
Brace yourselves, 9.0.1 hotfix is coming. Preliminary ETA is this Friday.
I want to update the community on the status up the next patch for World of Tanks. As you all know 9.0 is an update sets the stage for all the updates for the rest of the year. There were major functional changes that had to occur in this update to make that possible. This unfortunately led to some of the instability in form of game crashes and issues with framerate.We have already identified some of the issues and currently have a patch in QA testing. It will address many of the game crashes and some of the framerate issues. We want to get this patch out as soon as possible without introducing new problems.The current ESTIMATED timeframe for this patch is this Friday. It is subject to change depending on what is found by QA, but I wanted to make sure you are as informed as possible. If this estimate changes I will make another update. I will also update you if a second patch is required. We apologize for the disruption this update may have caused you, however we look forward to the advances that this patch will allow.Thank you all for your patience,Joshua Morris
World of Tanks Producer – North America