Jcm Router

For the main chat, that is what the author measured. An early version routing everything came to $106.73 over 309 logged requests against an $87.19 do-nothing baseline, with $17.12 of the loss in the main chat alone. Prompt caches are per model, so every mid-conversation switch came back with cache_read_input_tokens 0 and cache_creation_input_tokens 360370, rewriting the whole history at cache-write price. Subagents start cold and are still routed.

If the port is not listening at all, yes — while ANTHROPIC_BASE_URL points at localhost and nothing answers, every request fails, not just routed ones. That is why a supervisor respawns the router with backoff from 200 ms doubling to 5 s, and after three crashes inside 60 seconds it binds the port itself and streams every request upstream unchanged with routing off. A kill -9 of the supervisor, a reboot, or sleep is not covered.

Only when it is called. Jev receives a small state object — the user message capped at 6000 characters and the previous reply at 2000 — and answers three questions: model, effort, and whether this is a short follow-up. A 2.5 s timeout or any error forwards the request unchanged, and model plus effort are cached for the turn so a tool loop never switches halfway through. Override with !opus and Jev is not called at all.

Not exactly, and the repo is candid about it. MODEL_MIN_CONFIDENCE and EFFORT_MIN_CONFIDENCE both sit at 0.7 because an eval sweep found every model choice Jev acted on was correct at every floor from 0.4 to 0.9, so the bar was raised to a value that costs no measured savings rather than to fix errors. Running tune on real traffic put the money-optimal floor at 0.65, but that gap rests on four decisions, so 0.70 stands.

A small state object with the newest user message capped at 6,000 characters, the previous assistant reply capped at 2,000, and the previous routing for the conversation. Jev answers three questions: model, effort, and whether this is a short follow-up.

Start a prompt with !fable, !opus, !sonnet or !haiku and optionally !low through !max. Overrides beat every gate and guard, and if both model and effort are overridden Jev is not called. scripts/env-off.sh removes the settings key that points Claude Code at the proxy.

Only /v1/messages requests carrying a non-empty tools array are routed. Everything else, including chat title generation and other paths, passes straight through unchanged.