DETROIT — The CT6 was supposed to be the flagship sedan that led Cadillac’s rebirth. It was the first full-size Cadillac with rear-wheel drive in two decades, the only Cadillac offering a high-powered Blackwing V-8 and the only way to get Super Cruise, a driver-assist system that many critics say outperforms Tesla’s Autopilot.

But four years after its arrival, the car that former Cadillac chief Johan de Nysschen introduced as “prestige luxury reimagined” is kaput. The Michigan plant that stopped making it last week is slated to instead churn out electric vehicles starting next year.

GM looked at a number of options to keep the CT6 alive, GM President Mark Reuss said. But executives didn’t find a viable solution.”To transform the business you sometimes need to make tough decisions; this is one of those times,” Reuss said in an email to Automotive News. “But the Cadillac portfolio is in a great place. With the addition of the CT5 and CT4 sedans to the portfolio in 2020, Cadillac will have 94 percent coverage of the luxury market and the freshest luxury lineup in the industry.”

Though its life span was cut short, and it never seriously challenged the BMW 5 series in sales as envisioned, dealers say it did help lay the groundwork for what’s to come at Cadillac.

“It represented for me a new layer of design and performance and technology. That was a vehicle that they were hanging all their neat stuff on,” said David Butler, executive manager of Suburban Collection, a Michigan-based dealership group with stores in the Detroit area and California. “From the design all the way to the technology that was on that vehicle, we got a good glimpse of the way Cadillac is going.”

Super Cruise and engines with performance levels similar to that of the Blackwing eventually will be available throughout Cadillac’s lineup. The CT6 “affirmed that Cadillac is at its best when we lead in technology and design, and we will apply that formula to all future products,” Reuss said. “CT6 innovations will live on.”

When Cadillac introduced the CT6, it was expected to have Escalade-like appeal, said Mike Walls, general sales manager at LaFontaine Cadillac in Highland, Mich. Because the CT6 was aimed directly at Audi, BMW and Mercedes-Benz, the launch was an effective way to re-energize Cadillac, he said.

A booming SUV market and declining sedan sales compromised the car’s chances at success, said Jeff Schuster, president of the Americas operations and global vehicle forecasts at LMC Automotive.

“They really were focused on having that high-end car that seems to say that you’re a luxury brand,” Schuster said. But as even ultra-premium brands — known for smaller performance vehicles — launch high-end SUVs, a premium sedan may not give off the luxury appeal as much as it once did, he said.

GM originally planned to stop making the CT6 for North America in June 2019 under a restructuring plan that called for closing the Detroit-Hamtramck Assembly plant and four other North American plants. The company later extended production until Jan. 31. Last fall, it agreed to keep Detroit-Hamtramck open under its new labor contract with the UAW — but for EVs, not the gasoline-powered sedans it was making.

GM will continue to build the CT6 in China but doesn’t have plans to import it to the U.S. “Cadillac is surging in China,” Reuss said. “They need all the product they can get over there.”

U.S. sales of the CT6 declined from a high of 10,542 in 2017 to 7,951 last year, according to the Automotive News Data Center.

“They didn’t overbuild them. I think they were really being disciplined with it,” Schuster said.

“It was hugely important to demonstrate technology and advanced powertrains. From a technology standpoint, I think the question with that is, why hold [Super Cruise] to just CT6 for so long?”

Super Cruise launched on the CT6 in 2017. It’s still the only vehicle to have Super Cruise until GM extends it to the CT4, CT5 and Escalade this year.

The CT6 also is the only vehicle with a Blackwing, Cadillac’s 550-hp V-8. The engine has “become synonymous with performance,” Reuss said, but GM has not said whether the Blackwing will be available on other vehicles. Reuss said the “spirit of the Blackwing performance” will be seen in performance versions of the CT4-V and CT5-V.

The CT6 was comparable to the CTS, which went out of production last year. So if the CTS had a better incentive program, dealers would sell that car more easily, said Howard Drake, owner of Casa de Cadillac in Sherman Oaks, Calif.

Drake’s store sold about two CT6s per month out of about 40 total new vehicles sold.

News that GM was at least contemplating an end to CT6 production since late 2018 injected a sense of uncertainty into some customers’ purchase, he said.

“There’s a million things that go into a calculus like that, but it really hurt the momentum of the car,” Drake said.

But for others, it was incentive to buy one of the last U.S. models.

Butler of Suburban Collection said, “There is [demand] because the vehicle is going away and it’s really a vehicle that certain customers like.” His stores had more than a dozen CT6s last week and were still awaiting deliveries of some 2020 models. Last year, Suburban’s larger Cadillac stores sold about 10 CT6s per month. About a third of them had Super Cruise.

As CT6 inventory disappears, Butler will direct its buyers to the CT5. Although smaller than the CT6, it’s dealers’ “best hope” to keep those customers with the brand, he said.

Even dealers who sold few CT6s will miss the car because it often sells at a higher margin than other nameplates.

“Would my franchise be better off if I had a Blackwing, Super Cruise CT6?” Drake said. “Yeah, I think my franchise would be better for that.”