These journalists seem to be getting conflicting info. I do wonder if the AMG team confirmed the 6 cylinder to them and I've been left out of the loop. Roadshow mentioned the same thing:
https://www.cnet.com/roadshow/news/2022-mercedes-amg-sl-sl63-prototype-first-ride-review/?PostType=multi-image&ServiceType=twitter&TheTime=2021-09-21T18:16:00&UniqueID=F9AC4784-1B07-11EC-9F8E-1D9596E8478F&ftag=COS-05-10aaa0b
"The base SL will be the SL53, which will use AMG's turbocharged inline-six hybrid motor, and there should be a high-powered plug-in-hybrid model sharing the
GT63 E Performance's powertrain."
Also interesting:
"Stockmeier says the team looked to the original 300SL for inspiration, and the R232 will definitely be a lot more fun to drive than previous SLs. But AMG doesn't want the new SL to alienate existing customers by being too racy -- in fact, Stockmeier thinks it could be the next car for those that bought the now-dead S-Class convertible. "Of course we know the heritage of the car and we know the customers of the current one, and they shall be lucky when they buy the new one as well," he says.
"90% of the customers will never go to the track, and they want to have a comfy car as well, and that's what we need to provide. These are very valuable customers and we want to have them with us." It will also attract enthusiasts that want a performance car, though, and therein lies the new SL's real appeal."