Via [url=http://blog.counter-strike.net/index.php/2017/05/18748/]the CS:GO blog[/url] and Valve's Ryan:

[quote=Valve]- Guardian lobbies will now show full mission name in the nearby public lobbies list and game invites.
- Updated Guardian warning sound rules for players too far from the bomb site and lowered volume of warning sound.
- Fixed a bug where sometimes 9 players could join same team in War Games.
- Fixed offline with bots games not starting correctly after playing War Games online.
- When the daily War Games map rotation happens, servers will no longer shut down, but will instead seamlessly rotate to the new map group.
- Fixed a potential exploit in CS:GO engine reported by One Up Security.[/quote]

Rumor has it:

- Other than that, mostly translations from Translators Like You: https://github.com/SteamDatabase/GameTracking-CSGO/commit/5d334d61b0b826b8f9dd2a21671b3239ae58eb8e

- Size is ~15 MB, except ~25 MB on Linux (per [url=https://www.reddit.com/r/GlobalOffensive/comments/6dl56k/counterstrike_global_offensive_update_for_52617/di3idmn/?context=2]/u/csgodf[/url] and [url=https://www.reddit.com/r/GlobalOffensive/comments/6dl56k/counterstrike_global_offensive_update_for_52617/di3irsx/]/u/boommicfucker[/url])