Some basic info in the article here.
https://www.autoexpress.co.uk/merced...p-straight-six

If that is true, then it leaves the GT63 Coupe 2 doors as the only V8. That s great, it really makes it stand out. They didn’t do that in the SL and I feel it’s all a mess there: V8 for both 53 and 63 models. And a 4cyl engine as a starter. For what is supposed to be a special car. I hope the 4 cylinder doesn’t ever come to the GT Coupe, just to keep it apart from the lower models out there.

”The 53 should come with the 3.0-litre straight-six mild-hybrid from the CLE 53, tuned to 449bhp and 560Nm of torque. We expect a 0-62mph time of 3.9 seconds and a 183mph top speed.”

You're confusing some things. The V8 is in the GT 55 and GT 63, just like it is in the SL 55 and 63. The 53 (not 55) is the next lower entry model which gets the straight six just like the recently unveiled CLE 53. It's also mild hybrid. There's also a GT 43 coming with the same 4 cylinder engine as the SL 43.

Also, the strange thing is that the 4 cylinder in the 43 models is now the hand-built OMOE M139, so it's a true AMG engine, whereas the straight 6 in the 53 models is a tuned MB engine and not a hand-built AMG engine.

Yeap, you are correct… I got confused..

still, if the info is real it’s a better choice then the 4 cylinder engine

See above. That depends. The 4 cylinder is an actual hand-built AMG engine, whereas the 6 cylinder is a tuned MB engine and not hand-built and designed by AMG.

Will be interesting what actual difference performance wise is there between the M256 from lets say the 2019 E 53 and now the M256... M in the 2024 CLE 53

The 53 models have been anemic in the past but MB has juiced up the engine a bit. More HP and torque and a 12 sec. overboost feature. I like the V8 though...

For sure, I mean, at the end of the day still going to be better than a four cylinder. Cylinders count, I am not writing off the capability of the M139 but from my eperience the clyinders does count for smoothness and effortless driving/passing on the highway.