"Ubisoft is growing at an intense pace and our strategy is to ensure the strength of our global creative teams," said Ubisoft executive Christine Burgess-Quemard in a statement obtained by GameSpot.
The French publisher is reportedly acquiring "the assets and all of the personnel" of the Swedish studio, signaling that the transition will be made without layoffs.
Activision Blizzard, for its part, reported a strong quarter just last week but made no mention of the transaction. Massive's future was put into question after Activision and Blizzard merged, necessitating a streamlining of the portfolio at owner Vivendi.
Massive is presumably still at work on Soviet Assault, an expansion to World in Conflict. The game was due this fall but suffered some setbacks from the sell-off, leaving its release date unknown.