Via [url=http://blog.counter-strike.net/index.php/2016/09/15820/]the CS:GO blog[/url]:

[quote=Valve]The following changes are in the “1.35.4.7rc” CS:GO Beta depot.
[Gameplay]
– The first-person camera of players, spectators, and demo-viewers is no longer allowed to rise higher than their third-person head. This should prevent first-person players from being able to see from perspectives where their third-person head is not also exposed.
– When a player’s first-person camera is adjusted, bullets fired from both their client and server-side locations are also adjusted to emit from the corrected position.
– If for any reason the third-person player animation lowers a player’s head beneath the client’s first-person camera, the client’s first-person camera is lowered to stay at or under the height of their third-person head. This means that the third-person motion of the player is now represented more accurately from the first-person perspective.
– Third-person landing recovery animations are now weighted based on altitude traversed and duration in-air. Players landing from small jumps or falling from lesser heights will play more subtle landing animations.
– The anti-crouch-spam system has been changed to use degrading speed, instead of logging keypress-count. As before, the more often players crouch, the slower they will rise or lower. But this should now prevent bugs where players would instantly stand, or lose their crouch-spam penalty by moving a tiny amount. If players crouch even more, eventually they will just stay standing up.
– First-person and third-person crouch speed is now more closely related. The third-person player lowers more quickly to match the first-person representation.
– Players landing in crouch positions play a more subtle landing animation that raises their third-person head less noticeably.
[Misc]
– Lag compensation system will now reliably restore pose parameters responsible for animation layering which makes server-side hitboxes for lag compensated players better match client-side rendered models. (Thanks, /u/Spurks)
– Fixed a bug where player body pitch could improperly rotate the entire player entity inside lag compensation processing.[/quote]

Rumor has it:

- This prerelease update is a historic first for CS:GO, as it appears Valve has listened to those that want a beta branch in some form

- Wish to opt in? Right-click on CS:GO in your Steam library, go to Properties, go to the Betas tab, then select "1.35.4.7rc"
- If you don't see this branch offered, restart Steam
- To opt in for servers: run "+app_update 740 -beta 1.35.4.7rc" in SteamCMD

- SteamDB GameTracking services will be completely unavailable as it only keeps eyes on the public branch - be aware

- Size is ~15 MB