PorscheBoost would guess that means the GTS models features the X51 option or Powerkit as standard. As a reminder, Porsche offered an X51 Powerkit option for the naturally aspirated flat-6 motors of the 991 and past 911 generations as well. The 991.1 GTS offered the Powerkit as standard.
The naturally aspirated motors required a bit more work to massage output by 30 horsepower with new camshafts, cylinder heads, and a revised plenum. This is why the option was $17,800 in the past but now will likely be closer to $10k.
What is included? New larger turbos, new tuning, and improved cooling along with the Sport Exhaust option:
For potential buyers, the upgraded turbos make the GTS model a 911 Turbo light. With a tune alone, the GTS will comfortably exceed what the S can do with a tune. It's a factory turbo upgrade.
For those who plan to just leave things at a tune, the GTS will offer similar value as the 996 Turbo S model offered over the 996 Turbo. The 996 Turbo S came standard with the X50 option which meant larger K24 turbochargers compared to the K16 turbochargers of the standard 996 Turbo. This meant greater gains with aftermarket tuning.
The option of course will also be available to Carrera S owners who may want the power of the GTS models in the narrow body without the connecting light strip in the back.