On Tuesday we learned that Boston-based nuTonomy is being bought by tier-one auto supplier Delphi. Delphi is paying $400 million for the startup, plus about $50 million more in earn-outs. In return, it gets an extra arrow in its self-driving quiver. Four-year-old nuTonomy is developing an automated driving "stack"—the combined software programs that do everything from fusing sensor inputs that perceive the environment around a vehicle to facilitating the decision-making of where to actually drive.

"Our mission has always been to radically improve the safety, efficiency, and accessibility of transportation worldwide," said nuTonomy cofounder and CEO Karl Iagnemma. "Joining forces with Delphi brings us one step closer to achieving our goal with a market-leading partner whose vision directly aligns with ours. Together, we will set the global standard for excellence in autonomous driving technology."

Automotive suppliers like Delphi and Bosch are just as heavily committed to self-driving technology as OEMs like General Motors, Tesla, and Volvo. Last year, Delphi and Mobileye revealed plans for a production-grade autonomous system planned for 2019.

nuTonomy has been testing its driverless cars in Singapore and Boston (where Delphi has also been testing autonomous vehicle technology). The addition of nuTonomy's 70-odd engineers and scientists almost doubles Delphi's self-driving research team, and Delphi says that combining efforts in those two cities (and others) will see it deploy 60 self-driving vehicles in three continents by the end of the year.

It's yet another domino falling in the driverless car space, which has seen several acquisitions with hefty price tags of late. Last year, GM paid $1 billion for Cruise. In February, Ford splashed out a similar amount on Argo AI. And in March, Intel coughed up $15.3 billion for Mobileye. It almost makes Delphi's purchase look cheap.