The IPO, intended to repay a portion of the automaker’s government bailout, has been dubbed “Project Dawn,” the source said.

The source declined to be named because preparations for the IPO remain private.

The number of shares to be sold by the US government, the governments of Canada and Ontario, the United Auto Workers union healthcare trust and other shareholders has not been determined, the source said.

Sources previously told Reuters the IPO could raise as much as $20 billion, making it one of the biggest IPOs ever.

The US Treasury plans to sell about 20 percent of the 304 million GM shares it holds, reducing its stake in the top US automaker to below 50 percent, sources have said.

GM is not expected to issue new common stock in the IPO but plans to sell about $3 billion in mandatory convertible securities that convert into shares in the future, a person familiar with the plan previously told Reuters.

Meanwhile, in another and unrelated development, General Motors and China’s Shanghai Automotive Industry Corp signed a deal Wednesday that will see them work together on producing new engine and transmission technology.

Hu Maoyuan, chairman of SAIC Motor, China’s leading automaker by sales, called the deal a milestone that would see the two companies share key intellectual property and help SAIC move up the industry’s value chain.

“This is the first time a Chinese automaker has collaborated with a leading international group to develop a core technology while sharing intellectual property on a global scale,” Hu said at a signing ceremony in Shanghai.

“This boosts SAIC’s efforts to master the core technology and marks movement to the higher end of the value chain,” he added.

Engineers and researchers in Detroit and their joint venture’s research centre in Shanghai will develop a fuel-efficient engine and front wheel drive transmission, GM Vice Chairman of Global Products Operations Tom Stephens said.