Also, key talent had enough accumulated compensation so that they were no longer dependent on continuing salaries.

Early staffers had an unusual compensation system that awarded supersized payouts based on the project's value. By late 2015, the numbers were so big that several veteran members didn't need the job security anymore, making them more open to other opportunities, according to people familiar with the situation. Two people called it "F-you money."

In December, the car unit morphed into a standalone business called Waymo, and the system was replaced with a more uniform pay structure that treats all employees the same, according to a person familiar with the situation. Still, the original program got so costly that a top executive at parent Alphabet Inc. highlighted it last year to explain a jump in expenses. A spokeswoman for Alphabet, the holding company that owns Google and "Other Bets" like the autonomous car business