It should be only working in the private branch since 1.2.9 doesn't have working online multiplayer.
Here is the entire announcement copied from the discord server
For those of you who want to play the latest version (minus multiplayer), it's up on the "PRIVATE" branch. password for the branch is:
SnarSn4r5n4r
Just right click GRIP in Steam, properties, betas, input the above code and then switch to the PRIVATE branch in the drop down menu
I'll be writing up a proper changelist at some point. Just swamped with other dev stuff right now
Here's the biggest changes:
-Greatly improved vehicle physics and collision
-Vastly improved menu with full gamepad support and additional functionality in the garage
-Greatly improved arena mode and AI, plus an additional arena on Jahtra
-Improved current tracks visuals and flow/collision
-New custom tournament creator allows you to create your own tourneys
-4 player split screen supported, including ability to have one person on keyboard
-bunch of stuff I'm forgetting
There are bugs, indeed. So be sure to post them in the bug reports channel!
Hope you enjoy!