Size is ~65 MB (with Workshop Tools installed). More info will be edited in when available.
The SteamNetworkingSockets library (the heart of the Steam Datagram relay system used for communications to and from servers) has been brought up to version 12, and includes a few refactored protobufs plus a bunch of under-the-hood changes including support for multiple traffic "lanes" (in a nutshell, it's a quality of service/QOS method to ensure higher priority "lanes"/traffic gets a bigger slice of the bandwidth pie while lower priority traffic can get a little less)
Debugging effort on the game's audio system continues to take place with both sound libraries being updated to include some additional error detection and output whenever "soundinfo" is run
Although it was suspected that 3rd-party software may have been the culprit, issue reports remain, but /u/JeffHill thinks that "we're gradually closing in on the problem…"