I meant that companies like Anthropic are locking in users with proprietary formats in their harness where it's hard to leave.

Agree. Harness can not be a moat. There are many open harnesses and they are at least on par with the providers ones. It looks like Anthropic/OpenAI's approach to vendor lock-in is not so much the inference or the harness it is functional integration across the individuals and teams in a company. I don't think this will be a moat either, but I think it's all they have outside of compute.