Insider: after porting CS:GO to Source 2, there will be two versions of the game
Tyler McVicker, a well-known insider in the CS:GO community, in a video on his YouTube channel shared the information about Valve's work on porting the game to Source 2. He said that once the developers introduce a new engine, the shooter will be divided into two versions, one of which will run on Source and the other on Source 2.
Starting with CS:GO Source 2, there is really not a whole lot to talk about other than confirmation that yes, it is in development and when it does roll out, there will be a Source and Source 2 version of the game, similar to Dota 2 Reborn. This is something that many, including myself, have been predicting for a while. This is needed when you are porting an entire game to a brand new engine, you have to beta test the crap out of it.
The rumors about CS:GO being ported to a new engine first appeared several years ago. Since then, McVicker and other insiders have repeatedly shared information found in various sources that indirectly confirms the work on porting the game to Source 2. Valve, however, has never publicly confirmed these rumors.