Via CS:GO Blog:

GAMEPLAY

• Added the all new MP5-SD, available for testing Offline and in Official Casual and Deathmatch servers. It can be equipped in your MP7 loadout slot.

MATCHMAKING

• Lobbies advertised to nearby players and Steam Groups members will now expire after 5 minutes of the lobby leader’s inactivity.
• Added a way to start advertising single-user lobbies to nearby players and Steam Groups members from the permissions dialog.

NETWORKING

• Fixed a bug causing some players, especially on DSL connections, to experience high packet loss due to packets being delivered out of order.

PANORAMA

• Enabled Panorama UI on Windows XP and Windows Vista game clients.
• Enabled lobby chat when accept match popup is active.
• Fixed various multi-line messages clipping last line of text.
• Fixed unresponsive keyboard after typing and pressing ‘send’ in the chat panel.
• Allow sending a Steam message to recent teammates using new Steam chat.
• Spectator HUD elements now respect the cl_drawhud setting.
• Fixed reconnect button when it appears over lobby chat.
• Fixed MP7 walk up animation.
• Game state integration includes a field “round_totaldmg” to track total damage the player dealt.
• Various scoreboard bug fixes for different game modes.
• Various stability improvements and fixes.
• Fixed mapoverview icon scaling

HORIZON CASE

• Added normal maps to Desert Eagle | Code Red and P90 | Traction

PERFECT WORLD

• Improved reliability of downloading Overwatch evidence in Perfect World CS:GO game client.

MISC

• This update includes a change to “csgo.exe” which, while signed with Valve digital certificate, may still trigger warnings in certain anti-virus packages and require users to manually change their AV software settings to update correctly.