I Ran 6 MCP Servers Behind One Agent. Here's What the Token Bill Actually Looked Like.

I wired six MCP servers into a single production agent last month — filesystem, Postgres, GitHub, a custom CRM connector, a browser tool, and an internal search index. The promise of MCP is "USB-C for tools," and at one server, it really does feel that way. At six, things get interesting in ways the tutorials don't prepare you for.

This is what I measured, what surprised me, and the four changes I shipped afterward.

The Setup

The agent runs on Sonnet 4.5 with a 200k context window. Six MCP servers, all using Streamable HTTP (the post-2026-04 transport), all behind a single tool gateway. I'm logging every tool call — input tokens (the schema and arguments), output tokens (the response), and wall time.

# instrumented mcp tool call