After 20 years of Xbox Live being Microsoft's main service for playing games online, they're putting an end to the Xbox Live name and rebranding that specific service as a tier for GamePass. It's specifically going to be called "GamePass Core" and the price is still going to be the same as XBLG, but one major difference is members of this tier will now get access to a small selection of games that are a part of the GamePass service. Some notable games that will be part of the Core membership include Doom Eternal, Fallout 4, Gears of War 5, Hellblade, Ori and the Will of the Wisps, and Psychonauts 2. The "deals with gold" member benefit will also still be a part of this membership tier, just called "deal with gamepass" now.
I think it's pretty clear at this point Microsoft really wants everyone who is part of their online ecosystem to be a part of GamePass as I'm sure at this point this has become the biggest money maker for the Xbox brand (Phil Spencer has been very open about how Xbox this past decade hasn't been as on-top as they were during the Xbox 360 generation). Start things off slow by simply migrating people who were part of just XBLG to a "lesser" GamePass tier that is the same as XBLG but with a major new benefit of "now you can play these first party games for no extra cost," and people who really enjoy the small taste will likely upgrade to the Ultimate tier where they get access to over 100+ games.