Obsidian Entertainment is moving under Bethesda's management while the two studios work on a new Fallout game, according to Kotaku.
The management change is the newly reported development and remains attributed to Kotaku. It would place the Fallout: New Vegas developer more directly inside the part of Microsoft responsible for the franchise, rather than leaving it under the broader Xbox Game Studios structure. Neither the report nor the attached announcements describe Obsidian as leaving Microsoft or becoming part of Bethesda Game Studios itself.
The Fallout collaboration predates this reorganization. Kotaku reported in July, citing Bloomberg, that Obsidian was pivoting to a new Fallout project led by design director Josh Sawyer after changes to the studio's slate. That report cautioned that the strategy was still in flux. Bethesda director Todd Howard later confirmed that Bethesda was partnering with Obsidian on a Fallout game.
Obsidian made Fallout: New Vegas for Bethesda in 2010, long before both companies came under Microsoft. The present project is not Fallout 5, which Bethesda says is separately in preproduction, and no title or release date has been announced.