I4 future power enhancement already evident

[Honeywell]

Its probably just a few lines of software code...

 

[Honeywell]

An extra 54 torques is a useful 18% harder kick in the kidneys...

 

[RapidLotus]

Very interesting that Mercedes is reducing the power on their newest version of the M139. Same engine last year produced 412hp in the A45. Back in 2019 the engine was making that power. Mercedes-AMG Details Most Powerful 4-Cyl Ever, Makes 416 HP. In 2020 the M139 in the A45 was making 421. So it is not just the use in the Lotus that they are de-tuning it. I am wondering if these reductions are on paper only to appease governments and insurance companies.

Great video of the M139 being hand built. 2020 Mercedes A45 AMG ENGINE (421 HP) - PRODUCTION

Last but not least, 442hp is possible from the factory. How about once a tuning shop gets their try...
How Mercedes-AMG Got 442 HP From a 2.0-liter Four-Cylinder

 

[Autopsy]

If I recall correctly engine on sl43 has an electric turbo thus not the same as m139 on emira. Maybe it’s to get a more linear driving experience for the GT that sl43 is.