They seem to be expanding for the new IP they've been working on for the past 2 years. They are already quite large, probably would be the 4th largest Xbox studio currently, if the sale was already approved, and they might be the 3rd largest Xbox studio by the time the acquisition is actually approved. Have 380 devs on LinkedIn currently, which is ahead of Bethesda Game Studios on LinkedIn, though BGS seems to be underrepresented on LinkedIn, much like The Coalition.
Their official web page says Multiple unannounced projects https://www.zenimaxonline.com/careers
so more than one? We already know of the new AAA Ip that is using the new Engine.