After having officially bought Obsidian and InXile last month, Microsoft would not finish with studio buyouts. During the X02018, Phil Spencer had hinted that the Xbox division had great ambitions for the studios, in order to get more exclusives.
According to Klobrille's indiscretions on Twitter, which was the first to confirm that Microsoft bought Obsidian, reports today that Microsoft is eyeing another studio: Something to spice up this Monday, I can say that Xbox is in advanced negotiations (since several months) with a medium sized studio, which has historically worked with Playstation » can you read on his twitter account.
A tweet that generated many responses, including one that suggested that the studio in question could be "Insomniac Games," which recently brought Spider-Man to PS4. To which Klobrille replied "no". Other advanced names are Quantic Dream, Ready At Dawn, Supermassive.
In view of the recent information confirmed by Klobrille, it may well be that we are expecting a future announcement. For now, it is still a rumor, which requires follow-up. Other rumors already mentioned another studio bought by Microsoft, the particularity of Klobrille relates to this studio that would be close to Sony.