An HTTP proxy that puts the Anthropic Messages API in front of OpenAI-compatible model providers, and measures every request it forwards. Point Claude Code at shim and its calls are translated to OpenAI ChatCompletions and routed to your upstream — or passed through verbatim to a native Anthropic endpoint.

shim is a measurement layer, not a way to get cheaper tokens: /v1/metrics reports per-request latency and token drift, every request shim rewrites in flight is logged, and /v1/messages/explain returns the exact upstream body shim would send before a request leaves the box.

Install

brew install 1mb-dev/tap/shim
# or: go install github.com/1mb-dev/shim/cmd/shim@latest

Quick start

export UPSTREAM_API_KEY=<deepseek key>   # ADAPTER=deepseek by default
shim &                                   # serves 127.0.0.1:8082
ANTHROPIC_BASE_URL=http://127.0.0.1:8082 ANTHROPIC_API_KEY=shim claude

Then see what it did: curl -s localhost:8082/v1/metrics | python3 -m json.tool.

Docs