While the initial release focuses on balance tweaks--affecting Natascha and other slowing weapons--plus a few map changes, Valve notes that the beta program may also be used for "testing new technologies without the risk of breaking the game" and "running higher level, game-wide experiments (like doubling player health)."
Valve previously held a TF2 closed beta program with TF2 clans, focused on balancing the class-based shooter for competitive play. The forum for this new beta has separate feedback sections for 'public' and competitive play, showing attention to both.
This beta uses a completely separate installation of TF2, so you can still play the regular version when you please. If you own TF2, you can enter the beta by moseying on over to the Steam client's Library section and installing "Team Fortress 2 Beta" from your list.
Here's what's in the initial beta release:
Three Natascha variants:
- -40% damage
- -25% damage, -25% health
- Spin-up/down time increased, slowdown-on-hit effect falls off over distance.
Misc balance changes:
- cp_granary: new entrance added into the RED and BLU mid ramp room.
- cp_5gorge: 5 CP version of cp_gorge.
- Players being healed by a medic are immune to movement-impairing effects generated by hit-scan weapons.