Plenty of hosters provide that. Cerebras, for example, fabs their own ASICs (seperate from Nvidia), builds them into servers, hosts a number of open-weights models themselves in friendly jurisdictions, and offers SLAs for enterprise clients; it doesn’t get more “guaranteed” than that in AI Land, but there are tons of hosts to choose from.
This makes sense for first-party hardware businesses like Cerebras that are renting or selling their platform to developer businesses (second party) for the purpose of creating AI-based software tools which they will then sell as services to other businesses (third party), and I can see that guarantees could be written in a contract for the first-to-second-party relationship.
What I don't see is that any such guarantees can be effectively written or enforced in a second-to-third-party contract, where an AI SaaS company is selling their software service to companies that don't do their own development, and expect that the service they have contracted will produce reliable results.