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shunt

Quickstart

This walkthrough takes you from an installed shunt binary to a Claude Code session where a gpt-* model runs inside Claude Code’s own harness. Install shunt first — see Installation.

1. Configure

Section titled “1. Configure”

shunt ships with all providers preconfigured, so a minimal config only declares routing. Create shunt.toml (in the working directory, or ~/.config/shunt/shunt.toml):

# Exact model id -> provider
[[routes]]
model = "gpt-5.6-sol"
provider = "codex"     # reuses your ChatGPT login via `codex login`


# Or send every gpt-* id to the OpenAI API
[[route_prefixes]]
prefix = "gpt-"
provider = "openai"    # uses OPENAI_API_KEY

Validate it:

Terminal window
shunt check
# -> config ok

2. Provide the provider credential

Section titled “2. Provide the provider credential”

Pick the provider you routed to:

Terminal window
codex login                     # codex provider: ChatGPT subscription login
# or
export OPENAI_API_KEY=sk-...    # openai provider: API key

3. Run the gateway

Section titled “3. Run the gateway”
Terminal window
shunt run
# -> shunt listening on 127.0.0.1:3001

4. Point Claude Code at it

Section titled “4. Point Claude Code at it”
Terminal window
export ANTHROPIC_BASE_URL=http://127.0.0.1:3001
export ANTHROPIC_CUSTOM_MODEL_OPTION="gpt-5.6-sol"
export CLAUDE_CODE_ALWAYS_ENABLE_EFFORT=1   # so /effort maps to reasoning.effort
claude

Inside Claude Code, run /model and pick gpt-5.6-sol. Unmapped models (all your claude-* ids) keep working exactly as before — shunt forwards them to Anthropic with your own credential.

5. Verify

Section titled “5. Verify”

Test the gateway directly before (or instead of) opening Claude Code:

Terminal window
# Mapped model -> diverted to the provider (uses shunt's provider credential)
curl -s -X POST "$ANTHROPIC_BASE_URL/v1/messages" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"gpt-5.6-sol","max_tokens":16,"messages":[{"role":"user","content":"hi"}]}'

A JSON response starting with {"id":"msg_ means it worked. Inside Claude Code, /status should show the Anthropic base URL as http://127.0.0.1:3001.

Where to next

Section titled “Where to next”