The markets reacted with a drop of more than six percent in the share price, with trading briefly suspended in the aftermath.
Stellantis chief Antonio Filosa, an Italian veteran of Fiat, was brought in as CEO last July.
He is hoping to revive sales and profits at the world's fourth-largest automaker, in particular in Europe, where the shift away from combustion engines has sputtered.
"Stellantis today unveils FaSTLAne 2030 ... to accelerate growth and profit," it said, after announcing on Wednesday it had formed a joint venture with China's Dongfeng to share manufacturing, sales and engineering operations in Europe.
"This will result, between now and 2030, in more than 60 new vehicle launches and 50 significant refreshes, across all brands and powertrain energies," including range-extended electric vehicles, 24 hybrid electric vehicles and 39 ICE/mild hybrid electric vehicles, Stellantis said.
"In Europe, capacity is expected to be reduced by more than 800,000 units," it added.
This would represent a 20-percent reduction, with total European capacity estimated at four million units, according to an industry source.
This would be achieved by "repurposing plants", such as in Poissy outside the French capital, and "leveraging partnerships", such as in Madrid and Zaragoza in Spain, as well as Rennes in western France, it said.
The joint venture between Stellantis and Dongfeng would see the Chinese firm's Voyah EVs built at a Stellantis plant in Rennes for the European market, they said on Wednesday.
It said earlier this month that it was considering strengthening its alliance with Leapmotor so the Chinese group can produce its own cars at two of the European auto manufacturer's Spanish plants.
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