PvP multiplayer mode The Arena launched for Sea of Thieves in 2019, but Rare has announced that the mode will be shutting down when Season Six kicks off on March 10.
Following that, you will no longer be able to play the mode or earn any cosmetics exclusive to it.
Those who reached or passed Sea Dogs rank 5, however, will be awarded free, as-of-yet unreleased cosmetics as thanks for supporting the mode.
“In December 2020, we announced that we had stopped active development on The Arena.