"We made it easy for existing Xbox One S games to be updated to run with double the frame-rate when played on Series S as well. When games are updated,
existing games can query to determine whether they're running on the new console. "
UPDATE: For the authoritative take on Microsoft's new flagship console, Digital Foundry's full Xbox Series X review is …
www.eurogamer.net
"There may be the some consternation that Series X back-compat isn't a cure-all to all performance issues on all games, but again,
this is the GPU running in compatibility mode, where it emulates the behaviour of the last generation Xbox - you aren't seeing the architectural improvements to performance from RDNA 2, which Microsoft says is 25 per cent to the better, teraflop to teraflop. And obviously, these games are not coded for RDNA 2 or Series X, meaning that access to the actual next-gen features like variable rate shading or mesh shaders simply does not exist."
UPDATE: Sometimes, we just can't leave well enough alone. I returned to Xbox Series X to take a look at more Xbox One a…
www.eurogamer.net
Essentially, RDNA2 can run like GCN, so in backwards compatability mode you're getting the equivalent of a 12 TF GCN GPU, which would be something like the Vega 64. And through the XDK, developers can enable new graphical modes for this "Vega 64" class console. There's really no need to spread misinformation, when we already have good sources and a whole bunch of work by DF on this.