According to the PlanetsideBattles Twitch channel that broadcast the run at the mark last night, this is one record which has yet to be made official, as the current certified world record by the Guinness World Records happens to be for 999 players three years back for Man vs. Machine, which is a browser-based FPS.
Should this phenomenal number of players be part of the world record, you can be sure that the gold standard has been set – really, really high too, where future FPS battles are concerned. Can you imagine the amount of mayhem that occurs in such a setting? I do wonder how the servers are able to handle that many players at one go – pity the person who is playing with a slow connection.