AUTO_UPDATE=1 updates the server through Steam on every start. After Coffee Stain releases a patch, restart from the panel; the in-game Server Manager shows a version mismatch until then.
Experimental
To run the Experimental branch set SRCDS_BETAID to experimental in Startup and use Settings → Reinstall once. Every player must switch their game to Experimental in Steam/Epic too. Saves from Experimental cannot be loaded on the stable branch later, so back up before switching.
Verify files
If the server misbehaves after a patch (crash on start, missing assets), set VALIDATE to 1 in Startup and restart once: SteamCMD verifies and repairs the installation. Set it back to empty afterwards, because validation makes every start slow.