By Blake BrittainJuly 20 (Reuters) - A federal judge in San Francisco on Monday signed off on artificial intelligence company Anthropic's landmark $1.5 billion settlement of a class action lawsuit brought by a group of authors who ‌accused it of misusing their books to train its AI chatbot Claude. U.S. District Judge Araceli ‌Martinez-Olguin granted final approval of the settlement, the largest known settlement of a U.S. copyright case, rejecting arguments that it was too ​small. The authors' lead attorney, Justin Nelson, welcomed what he called a "historic settlement." The settlement spurred objections from some authors who argued it was ‌not large enough, overcompensated the plaintiffs' attorneys ​or wrongly excluded some copyright ​owners. Some authors and publishers opted out of the ​settlement and have filed separate lawsuits against Anthropic that are still ongoing.