There are two ways to let an agent use your product.

A) Ship an MCP server. Define tools, describe them, run a process, the model calls them.

B) Ship a CLI. yourtool do-the-thing --json. The agent runs it in a shell like a human would.

For about a year the answer was obviously A. In 2026 a lot of teams quietly went back to B — and the ones who did aren't posting "MCP is dead" takes, they're posting latency graphs.

Here's what's actually happening. Five costs, in the order they hit you.