Formula One has formally rejected Andretti and Cadillac's joint bid to enter the championship in 2025 or 2026 but has left the door open for the team to enter in 2028.
The bid likely would have relied on a Renault engine deal in the short term, although General Motors has registered to join F1 as an engine manufacturer from 2028 onward.
F1 rejected the project in its existing form on Wednesday but said Andretti has a good chance of joining in 2028 if General Motors follows through on its plans to build its own F1 power unit.
"Our assessment process has established that the presence of an 11th team would not, on its own, provide value to the Championship," F1 wrote.
The decision means F1's grid will remain at 10 teams and 20 drivers for at least the next four years.
Andretti responded to the news with a statement later Wednesday.
"Andretti Cadillac has reviewed the information Formula One Management Limited has shared and strongly disagree with its contents," the statement said.
"Andretti and Cadillac are two successful global motorsports organizations committed to placing a genuine American works team in F1, competing alongside the world's best.
"We are proud of the significant progress we have already made on developing a highly competitive car and power unit with an experienced team behind it, and our work continues at pace."
Opposition to the project goes deeper than the logistics of the engine in the car. Early last year, team founder Michael Andretti, son of 1978 world champion Mario, accused F1's 10 existing teams of being "very greedy," saying of their opposition: "It's all about money."
Responding to Wednesday's news, Mario Andretti posted on X, formerly Twitter: "I'm devastated. I won't say anything else because I can't find any other words besides devastated."
F1 was not bound by the opinion of existing competitors, but the majority of the sport's 10 teams have been opposed to a new team coming in as it would dilute the prize money shared among them. That opposition has undoubtedly helped shape F1's decision.
F1 also said it did not believe Andretti could come in and be truly competitive with a customer deal.
"The most significant way in which a new entrant would bring value is by being competitive," the F1 statement said. "We do not believe that the Applicant [Andretti] would be a competitive participant."
Even before Wednesday's decision, Andretti rejected this suggestion and insisted the team would have been ready to race by 2025.
F1 disagreed with that concept on the basis "that this would involve a novice entrant building two completely different cars in its first two years of existence."
"The fact that the Applicant proposes to do so gives us reason to question their understanding of the scope of the challenge involved," F1 said.
Andretti-Cadillac has hired big names in the racing world, including former Renault technical chief Nick Chester, and has set up a satellite UK base in Silverstone to support the team's global racing hub in Indianapolis.
It has also been testing in Toyota's Cologne wind tunnel with a 60% size model designed to the current regulations.
Many in F1 were also skeptical about the logic of Andretti joining the grid in 2025 before a major regulation change comes into effect for the 2026 season.