OpenRouter | shunt

Route mapped models to OpenRouter's Anthropic-compatible endpoint — one API key, hundreds of models.

OpenRouter aggregates many model vendors behind one API key, and exposes an Anthropic-compatible endpoint — shunt forwards Claude Code’s Messages request as-is and injects the OpenRouter key. There is no built-in preset, so the upstream declares kind and base_url explicitly.

Quick start

Let a coding agent wire it up for you — for a provider without a named blueprint, shunt add injects the documentation URL into its generic research guide (offline and read-only; the agent edits the config, the command never does):

shunt add upstream https://openrouter.ai/docs --print | claude

Or follow the manual steps below.

Configure the upstream

[[upstreams]]
name = "anthropic"
provider = "anthropic"   # keep Anthropic as the default for unrouted models (e.g. claude-*)

[[upstreams]]
name = "openrouter"
kind = "anthropic"
base_url = "https://openrouter.ai/api"
auth = { mode = "api_key", env = "OPENROUTER_API_KEY" }

[[routes]]
model = "anthropic/claude-opus-4.8"
provider = "openrouter"

Ordered [[upstreams]] replace shunt’s built-in providers, so the config must declare the anthropic default it still falls back to (server.default_provider defaults to anthropic).

The legacy [providers.openrouter] table form remains supported — but do not mix [[upstreams]] and [providers.*] in one file.

Credentials

export OPENROUTER_API_KEY='...'

Never write the key into the config. shunt check validates the config’s structure but does not read the key’s value — if OPENROUTER_API_KEY is unset, the first request routed to openrouter returns an authentication error.

Models

OpenRouter model ids are vendor/model slugs (e.g. anthropic/claude-opus-4.8) — browse the OpenRouter model catalog and add one [[routes]] entry per slug you want reachable. Select a routed id in Claude Code via ANTHROPIC_MODEL, ANTHROPIC_CUSTOM_MODEL_OPTION, or a subagent’s model: frontmatter. To surface an entry in the /model picker instead, advertise a claude-prefixed alias with a [models.upstream_model] map — see Model Discovery.

Verify

shunt check    # -> config ok
shunt run
curl -sS http://127.0.0.1:3001/v1/messages \
  -H 'anthropic-version: 2023-06-01' \
  -H 'content-type: application/json' \
  -d '{"model":"anthropic/claude-opus-4.8","max_tokens":16,"messages":[{"role":"user","content":"Reply with OK."}]}'

Confirm the response’s x-gateway-upstream header names openrouter, then point Claude Code at shunt.