Has anyone made BYOK work / Harness as a service ?

I'm building an agentic SaaS for developers and founders.

One thing I'm struggling with is AI costs. I want to offer an agent with a lot of features, but I'm worried about inference costs. I also don't want to limit features too much or constantly make users think about usage limits. I'd rather let users decide the workload they want to put on the system.

One idea I had was BYOK (bring your own key). Users would provide their own OpenAI, Anthropic, or Gemini API key, and I would charge only for the harness, infrastructure, monitoring, and product itself.

The more common approach seems to be charging users and giving them credits that get consumed as they use the product.

lmk your opinions :3