Via the CS:GO blog:

CS:GO

Added new Gamma weapon case featuring 17 community-created weapon finishes and all-new knife finishes.
Operation Wildfire Access Pass is no longer available for purchase.
XP

New CS:GO players will get a significant earned XP boost multiplier in Recruit and Private Ranks.
Competitive matchmaking for new CS:GO players is now unlocked sooner, as soon as they rank up from Recruit to Private Rank 2.
PRIME BETA UPDATE

CS:GO accounts will be Prime if they have verified their phone number and achieved at least Lieutenant Rank 21 or have earned a Service Medal.
Prime accounts can now select to search only for other prime accounts in competitive matchmaking.
When matchmaking with a party lobby, all party members must be Prime to have the Prime-only option available.
SOUND

New sound cue for shooting with low ammo.
Upgraded sound fidelity, reduced distortion for Mag7, M249, Negev.
New smoke sound to reduce interference with bomb defuse sound.
New sound for text chat messages in party lobby.
MISC

In classic game modes any money earned by a player mid-round will no longer be available for spending during the same round (i.e., SMG purchases are no longer possible during competitive pistol rounds).
Suicide or disconnect compensation will no longer be awarded in warmup or during freezetime period.
When controlling the bot and surviving round running out of time, the controlling player is now eligible to receive end of round money.
Removed a legacy 2.5 seconds spawn grace period for players who reconnect to the round after freezetime is over.
Increased upper limit on possible mp_halftime_duration values to 5 minutes.
Added server convar sv_spec_post_death_additional_time that allows adding a delay for spectators between the death of a spec target and the switch to a new target.
The convar sv_alltalk has been replaced with sv_talk_enemy_dead and sv_talk_enemy_alive.
Classic Casual now defaults to team-restrict communication for living players.
Mac

Fixed appearance of fonts in the community browser and console.
Fixed some bugs with setting fullscreen resolution.
Set all Mac players to use Raw Mouse Input by default since this is a better experience for most players. Players can manually revert to not using raw mouse input if that is what they prefer.
Rumor has it:

Script changes which includes the sound enhancements, and an early peek at the item schema update: https://github.com/SteamDatabase/GameTracking/commit/625aa3e069cd87e4c70e3f8bd8a7063fe8a35640

Strings for the new Gamma Case, and updated strings for Prime: https://github.com/SteamDatabase/GameTracking/commit/e240cba0e11d6b37011ffe8eaeb478920799d73c

Hey! Are you fluent or near fluent in a non-English language and want to help translate the new and revised strings? Consider signing up to volunteer on the Steam Translation Server
In case you're wondering how I'll personally handle the transition from "OS X" to "macOS" with Sierra (10.12) with these posts, "for Mac OS X/macOS" will be used until El Capitan dies off

Of course, however Valve handles it is up to them
Size is ~80 MB