After the launch of Marathon's new Vault Breakers PvE mode, which Bungie was seemingly implementing as a way to improve player retention, the game saw a sizeable improvement in concurrent player counts, peaking at 14,771 concurrent players on Steam ( via SteamDB ). Since Vault Breakers launched, however, the numbers have started trending down again.

The Steam player tracker shows that, immediately after the Vault Breaker update launched, Marathon's player count peaked at 14,809 concurrent players—the highest it's been since mid-June following the free week. At the time of
writing, daily concurrent player counts are fluctuating between 2,000 and 7,000 players, with even those numbers trending down just a week after the PvE update.