I couldn't find anything on Google's sites that clarify this point either way. But this is in Wikipedia's entry for Stadia (for whatever that's worth):

> Stadia is not similar to Netflix, in that it requires users to purchase games to stream via Stadia rather than pay for access to a library of games. While the base service will be free, a Pro tier monthly subscription allows users to stream at higher rates for larger resolutions, and the offer to add free games to their library.