Players won't need to buy the main game to play it.
A free-to-play battle royale mode, known as RedSec, will be introduced with the season one update in Battlefield 6 tomorrow.
According to the Battlefield Twitter account, the mode will be free-to-play, and players don't have to buy Battlefield 6 to play it.
Eyes up. Plates on. #REDSEC arrives tomorrow at 8:00 PT / 15:00 UTC
The mode has been in testing, and several changes based on player feedback have been made, as stated on the Battlefield 6 Steam page.
Author's summary: Battlefield 6 gets a free battle royale mode tomorrow.