FIA President Mohammed Ben Sulayem has confirmed that Andretti would be guaranteed "one of two" power units for its Formula 1 entry, if commercial terms are agreed.
The prospective team has reached a crucial moment in its bid to join the grid, as it now enters the final phase of the entry process which involves commercial discussions Formula One Management (FOM) in its position as Commercial Rights Holder (CRH).
Both F1 itself and the 10 existing teams have been lukewarm towards the Andretti bid, with an agreement vital to ensuring the team can get onto the grid for either 2025, or most likely 2026.
Even though Andretti's bid comes with General Motors backing through the Cadillac brand, it is unlikely that the OEM would have an in-house F1 power unit ready - meaning Andretti would be forced to be a customer team.
This scenario is covered under Appendix 6 of the Sporting Regulations whereby the FIA will allocate a team without a power unit supply one from whichever of the existing manufacturers supplies the fewest teams.
As things stand in 2023, this would either be Honda/Red Bull Powertrains (RBPT) or Renault who currently only supply Red Bull and AlphaTauri, and Alpine, respectively.
The other suppliers Mercedes and Ferrari each provide units for three squads, including their own works outfits, with Ben Sulayem confirming the process would take place.
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"For the time being, Andretti has to agree on one of the two engines," Ben Sulayem told select media including RacingNews365.
"It works that, with the rules, nobody can say no to them.
"If all the teams say no [over a power unit supply] it goes the FIA [who] has the power to go on and say: 'The least two [suppliers] being used, let me put them in the draw and you take one.
"It's no secret that it is either Alpine or Honda, and one of them would win because that is the rules."
For the engine regulation rules reset coming for 2026, even more manufacturers are signed up with Audi entering as a works squad with Honda returning once again in addition to Ford joining as technical partner to Red Bull Powertrains.
Whilst GM/ Cadillac is not signed up to produce a power unti, the OEM could decide to join at a later date once the Andretti project is up and running, something Ben Sulayem is "optimistic" over.
"We are demanding that and we will see it," he said.
"Engines are not built in four years and five years, this is F1, the pinnacle, this is the efficiency, this is where it counts.
"Imagine having F1 more OEMs and more PU manufacturers, nobody can control and say: 'Ok we're raising the price' or: 'Oh, you have to vote this way' [in regulation changes].
"I am optimistic about GM coming in with a power unit. I am very optimistic.
"In the last 20 months to have two major OEMs which are Audi and Andretti/GM, and to have a power unit from Audi.
"We are on the right track of having a power unit from Cadillac, I think that is an achievement."