An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include: Added 64-bit support for Windows/Linux client and server Should include performance improvements for most users Bugs can be reported here: Fixed an exploit related to uploading invalid custom decals that would crash other clients
Doesn’t look like they bothered to update their macOS client to 64bit. Currently the game is unplayable on new versions of macOS.