The only true MMOFPS PlanetSide 2 set a new Guinness World Record for Most players online in a single FPS battle. Btw, we found some more interesting shooter-related World Records:
SOE's free-to-play MMOFPS achieved this record by having partnered up with the community PlanetSideBattles and saw 1,158 players simultaneously in one instance via PlanetSide 2's Jaeger competitive server. The huge showdown took place on the Hossin continent involving all three fractions.
Back in 2012 Swedish developers MuchDifferent claimed the record for Most players taking part in a single online battle in a FPS video game with 999 players simultaneously in Man vs. Machine, a browser-based FPS, solely developed to achieve this new benchmark.
But did you know, the Guinness World Record for Most players online simultaneously on one online shooter server is being hold by Mail.Ru Games for Crytek's f2p FPS Warface. A total of 145,012 players have been recorded on the Alfa server at one time, on 26 January 2013.
This number was surpassed by another record for Most players online simultaneously on one MOG server, also physically on a Russian server on 21 January 2013, on which a total of 190,541 players battled simultaneously on the war zones.
The world record for most peak concurrent users (PCU) in an FPS should go to CrossFire, as mega-publisher Tencent reported almost 4 mio. players in 2013, but this for some reasons is not an official Guinness World Record.
PlanetSide 2 is available on PC and sooon on PS4, check out full details at SOE's official site.
PlanetSide 2 - Anniversary Trailer