Musk fires back at OpenAI attorney

CNBC's Kate Rooney reports from the Oakland courthouse on the fourth day of the Elon Musk vs. OpenAI trial. Musk is being cross-examined by OpenAI's lawyers, with heated exchanges over the nonprofit's shift to for-profit and Microsoft's investment. The trial centers on Musk's claim that OpenAI executives cannot keep nonprofit protections while profiting. - Elon Musk is on the witness stand for the fourth day of his lawsuit against OpenAI. - Musk and OpenAI's lawyers have had fiery exchanges during cross-examination. - Musk argues OpenAI cannot retain nonprofit goodwill while reaping for-profit benefits. - Musk called his $38 million donation to OpenAI a 'foolish' act. - Microsoft's $10 billion investment in OpenAI is a key point in the case. - The defense argues Musk tried to control OpenAI and was aware of its direction.