Of which almost all mechanics will be exactly the same. Some of the top-level stuff might have different names or different organization... but the actual game will be the same.
Species will all get like 3 to 5 abilities, of which many will be the same as we already have. Combat will still be d20+STR or DEX+prof bonus versus AC. Spells will be DC 8 + ability mod + prof bonus. Saves are the same... damage is the same... the process of skill checks the same... the Classes we've seen have had most of the same abilities except the level acquired might be a little different on some. How and when you get Feats and ASIs are the same. Monster stat blocks will look virtually the same except for perhaps if they add a few more monster abilities to each block like other companies have done. Actions are virtually the same except some name changes and reorganization. Conditions mostly the same except for a few things from the game previous that are now being called "conditions". The equipment lists will have all the same stuff in it for the most part, the armors and weapons lists will look the same as we have except there might be some additional mechanics and features added to them.
Need I go on? I mean its no different than Level Up being considered the same game as 5E except for a lot of extra stuff layered across it. But the underlying system chugs along the exact same way. Same game... just looks a bit different on the surface.