Via the Steam Store:
An update has been released for Portal 2.
- Fixed crashes on multi-core and multi-CPU systems that can allocate more than 32 threads.
Portal 2 update for March 5, 2018
View all patches · Build 2577676 · Last edited August 11, 2018 – 09:06:01 UTC
by 
Wendy
Loading changed files in portal 2 common…
Loading changed files in portal 2 win content…
Loading changed files in portal 2 mac content…
Loading changed files in portal 2 client binaries…
Loading changed files in Portal 2 linux content…
Changed files in this update