Civil breach of contract. Anthropic's TOS explicitly say you can't do what Kimi is alleged to have done.
This is true, but Kimi also has a variety of defenses. Kimi can't raise unclean hands if Anthropic systematically violated others' terms of use, but it can raise copyright misuse (which is similar in some respects to unclean hands) as well as lack of standing to enforce restrictions in the contract due to the third party beneficiary principle (i.e., Kimi would argue that Anthropic cannot sue Kimi for derived IP that rightfully belongs to third parties whose terms of use were violated by Anthropic, and the proper party to sue Kimi, if any, would be those third parties). That latter argument usually fails in small-scale cases (ProCD) but has been successful in larger ones where the alternative would be anticompetitive.