Solo matchmaking is an experimental feature implented into DOTA 2 Test Client. There are some other minor updates like the number of reports you can make. It has been reduced to two per week. Read the full list of updates below:
Added Solo Matchmaking option. This is an experimental feature that will match you with players who also queued without being in a party. This is the first step in a series aimed at improving the matchmaking system.
COMMUNITY - Reduced the number of negative reports per week to 2 as part of our ongoing efforts to improve and tune the reporting and ban systems.
GAMEPLAY - Elder Titan: Fixed Legacy Keys - Drow Ranger: Fixed Frost Arrows slowing Spirit Bear for the full creep duration - Tusk: Fixed Walrus Punch having 1 less second of slow than intended. - Tusk: Fixed Armlet sometimes causing Walrus Punch to disappear after using Snowball.
PERFORMANCE - Reduced memory usage on systems with 2GB of RAM or less