The final expansion of The Binding of Isaac: Rebirth took a while to reach us. The Binding of Isaac: Repentance was first announced back in 2018, and there was a delay of a few months from December 2020 to March of this year as it slowly approached release.
Now that it's here, players are flocking back to the roguelike en masse: The Binding of Isaac: Rebirth recently broke its concurrent playercount record on Steam set in October of 2015.
And there may be another reason for players to stick around a while. After Repentance's release, modders dug around in the game's code and found signs of a native online co-op mode, and even managed to get it working with up to four players.
Online co-op was already possible through Steam's Remote Play Together feature and via Parsec, but both can result in latency and bandwidth issues depending on your internet speed. Native co-op for The Binding of Isaac would be a great addition to a roguelike that requires so much precision, and a lot of players are hoping the recently discovered code may point to an official co-op update in the future, though it hasn't been formally announced.
Reports from players trying the native co-op mode vary. Some are reporting crashes, disconnections, or trouble getting the mode working at all. Others have had more success and say it performs better than remote play options.
If you're interested in trying it out yourself, here's a quick instructional video on how to get it running.