Elon Musk’s claim that he was mistreated by his OpenAI co-founders failed after nine California jurors returned a unanimous verdict that his lawsuits had been filed too late.

Even as protests increase, the collapse of Mr. Musk’s suit against OpenAI and Sam Altman will speed up the artificial intelligence juggernaut.

The decision is a win for OpenAI in a trial that pitted Musk against OpenAI and two men with whom he co-founded the company in 2015: OpenAI’s chief executive, Sam Altman, and its president, Greg Brock...