MCP stdio vs Streamable HTTP
| Area | stdio | Streamable HTTP |
|---|---|---|
| Best fit | Local subprocess | Deployed remote service |
| Network port | No | Yes |
| Auth | OS/process/config boundary | HTTP auth/OAuth/token boundary |
| Scaling | One process per host pattern | Normal service scaling |
| Operations | Simple local lifecycle | Gateway, TLS, metrics, load balancing |
Decision rule
If the host should launch the server on the same machine, start with stdio. If multiple users or hosts need a shared service, use Streamable HTTP.
Do not choose by performance folklore
For many agent workloads, downstream APIs and model latency dominate. Choose the transport that matches trust and deployment boundaries first, then measure.