Valorant's Deathmatch mode will feature 10 players, just like the standard mode, but this is the first mode in Valorant that's not team-based, so every person plays for themselves. The objective is to get as many kills as possible, so there are no spike plants or defuses. There are also no abilities, and everyone has unlimited money to buy any weapon they like when they spawn.
Many players have been requesting for a Deathmatch mode since Valorant went into Closed Beta back in April, and it's a great way to warm up for an actual standard match. Players can leave and enter Deathmatch games whenever they want with no penalty.
Riot notes that the free-to-play Deathmatch mode is still on beta test, but they plan to release it permanently
You can read more about the new Valorant agent here.