The ChatGPT developer OpenAI has countersued Elon Musk, accusing the billionaire of harassment and asking a US federal judge to stop him from "any further unlawful and unfair action" against the company. OpenAI was co-founded by Musk and its chief executive, Sam Altman, in 2015. However, the two men have been at loggerheads for years over its direction as it transitions from a complex non-profit structure into a more traditional for-profit business. Musk sued OpenAI over its restructuring plans about a year ago, accusing it of betraying its foundational mission by putting the pursuit of profit ahead of the benefit of humanity. He dropped the suit in June, but then filed a fresh one in August.