Model-in-the-loop tool invocation (MCP) and deterministic CLI scripts reach roughly equivalent task capability (~83% accuracy), but the architecture diverges sharply on reuse, speed, and token cost — CLI can be up to 75x cheaper because scripts run thousands of times with no model round-trip. The choice of tool abstraction therefore buys cost and latency, not capability.
It reframes the MCP-vs-tooling debate: the decision should be driven by amortization economics and latency budgets, not by assumed capability differences. Any workflow executed repeatedly should be compiled out of the model loop.
For any agent task with a stable, repeatable procedure, pushing execution out of the model loop into deterministic code trades inference cost and latency for scripting/exploration effort — and capability is largely preserved.
Capability is a wash: both CLI and MCP achieve ~83% accuracy.
CLI beats MCP in reuse, speed, and cost.
CLI scripts can be written once and run thousands of times without model-in-the-loop overhead.
CLI can be up to 75x cheaper in terms of token cost.