While the news was broken by Official Xbox Magazine just after Christmas, Tomb Raider community manager Meagan Marie revealed a few more details about the multiplayer in the upcoming reboot on the game's official forums.
"Tomb Raider will include a multiplayer offering thanks to the hard work of our sister-studio, the hugely talented Eidos Montreal," Marie stated. "The team at Eidos Montreal has been working away at the multiplayer while we focused everything on the single-player offering."
Eidos Montreal was the studio responsible for Deus Ex: Human Revolution, and shouldn't be confused with the recently formed Square Enix Montreal, which will head up future Hitman titles. Having two studios handle the single- and multiplayer portions of a game separately isn't a new strategy, but is certainly one that has been rather hit-or-miss over the years.
We won't know just how Tomb Raider's multiplayer works out for a few months, but at least we now know that Crystal spent all their time and energy making the core game as strong as possible.