Release notes for the 3.8.x revisions of CRYENGINE Engine as a Service.
Steam Beta Branch
In order to opt-out of the Steam auto-updates you simply need to join a different "beta" branch in which we're archiving previous releases, starting from 3.6.5.
To do this, right click on "CRYENGINE" (not Sandbox) in your Steam library, click on Properties, click on "BETAS" tab and then you'll be presented with a drop-down list where you can opt-into different engine revisions. Note that 3.7.x and 3.8.x versions will be at the bottom of the list.
In order to return to the "main" branch which receives auto-updates, simply chose the "NONE - Opt out of all beta programs" option.
You must opt in to the Beta on the CRYENGINE app, not the CRYENGINE Sandbox app. The Sandbox app is a child of the CRYENGINE app and follows what it does.