Claude Code Setup (Anthropic Skin)

Point Claude Code (or the Anthropic Agent SDK) at Surplus and route every request through the marketplace — cheapest healthy seller, on-chain settlement — with no local proxy. Surplus implements Anthropic's Messages API surface (the "Anthropic skin"), so Claude Code talks to it the same way it talks to Anthropic.

It's also model-agnostic: you can run Claude Code on Claude or on GPT, GLM, Llama, Gemini, DeepSeek — any catalog model — through the same Anthropic wire.

For the full endpoint reference, see Anthropic Messages API.

1. Get a buyer key

Sign in on the Buy page with your wallet and create a buyer API key (inf_…). Fund it with credits, or set up a USDC allowance on the settlement contract. (Per-request x402/MPP payment is not used by the skin — Claude Code authenticates with the buyer key.)

2. Configure Claude Code

That's the whole required setup — three variables:

bash

export ANTHROPIC_BASE_URL="https://api.surplusintelligence.ai/anthropic"
export ANTHROPIC_AUTH_TOKEN="inf_your_key_here"
export ANTHROPIC_API_KEY=""        # important: must be empty so it doesn't override the auth token

Then run claude as usual. With no model variables set, Claude Code uses its built-in default models and the marketplace routes each request to the cheapest healthy seller for them.

Why ANTHROPIC_API_KEY=""? Claude Code prefers a cached ANTHROPIC_API_KEY (or a claude.ai login) over ANTHROPIC_AUTH_TOKEN. Blanking it forces your Surplus key to be used.

3. Choosing models (optional)

Setting models is optional. By default Claude Code uses its built-in models; the marketplace serves them like any other request. Set the variables below only when you want to pin a specific model, control cost, or run on a non-Claude model.

Claude Code has two model slots:

Variable	Slot	Used for
`ANTHROPIC_MODEL`	main	the primary agent loop
`ANTHROPIC_SMALL_FAST_MODEL`	small/fast	high-volume background tasks (titles, summaries, topic detection)

bash

export ANTHROPIC_MODEL="claude-opus-4.8"
export ANTHROPIC_SMALL_FAST_MODEL="gpt-4o-mini"

If you pin one slot, it's best to pin both (the small/fast slot is high-volume). Whatever model is used — a default or one you pin — must have a live offer in the marketplace; if it doesn't, those calls return a 503 / overloaded_error. Check the Market Prices page or GET /v1/models for what's live.

Newer Claude Code versions also read role-specific overrides (for the /model switcher and subagents), all optional:

bash

export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4.8"
export ANTHROPIC_DEFAULT_SONNET_MODEL="claude-sonnet-4.6"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="claude-haiku-4.5"
export CLAUDE_CODE_SUBAGENT_MODEL="claude-opus-4.8"

You can also use floating tags — ~anthropic/claude-opus-latest, ~anthropic/claude-sonnet-latest, ~anthropic/claude-haiku-latest — which resolve to the current flagship.

Run Claude Code on non-Claude models

Because the skin routes by model name, just point the slots at any catalog model:

bash

export ANTHROPIC_MODEL="glm-4.7"            # or gpt-5.5, deepseek-v4-pro, gemini-3.1-pro, …
export ANTHROPIC_SMALL_FAST_MODEL="gpt-4o-mini"

A common cost-saver is a strong main model with a cheap small/fast model, e.g. ANTHROPIC_MODEL="claude-opus-4.8" + ANTHROPIC_SMALL_FAST_MODEL="gpt-4o-mini". Friendly -latest aliases work across families too (glm-latest, gpt-latest, deepseek-latest, …).

Text and tool use work on every model. Extended thinking is Claude-specific — non-Claude models won't return thinking blocks (the request still works). Smaller models follow the agent's tool protocol less reliably on complex multi-step tasks.

4. Verify

In Claude Code, run:

/status

It should show:

Auth token: ANTHROPIC_AUTH_TOKEN
Anthropic base URL: https://api.surplusintelligence.ai/anthropic

Ask it something simple ("reply with one word — pong"), then try a tool task ("read package.json and tell me the name field") to confirm the agent loop. You can watch usage on the Buy page as your credits settle.

5. Optional: routing controls

The skin honors the same marketplace controls as the OpenAI surface — set them in the request body (the Anthropic SDK passes through unknown fields), or use the minimum-discount mirror:

Provider pin / allow-list: "provider": "venice" or "provider": ["venice","openrouter"] (the OpenRouter {order|only} object form is accepted too).
Host pin: "provider_base_url": "https://api.openai.com/v1".
Price cap: "max_price_per_1m": 5.0 (USD per 1M input tokens).
Minimum discount: set ANTHROPIC_BASE_URL="https://api.surplusintelligence.ai/anthropic/min50" to only route to sellers ≥50% cheaper than reference.

Troubleshooting

Symptom	Cause / fix
`401 authentication_error`	Missing/invalid key. Ensure `ANTHROPIC_AUTH_TOKEN` is your `inf_…` key and `ANTHROPIC_API_KEY=""`.
`503 overloaded_error` / "No available sellers for model 'X'"	Model `X` has no live offer right now. Pin that slot to a model with active liquidity (check `GET /v1/models` / Market Prices) — and if you pin one slot, pin both.
`404 not_found_error` (price threshold)	Your `max_price_per_1m` / `min{N}` is below any seller — raise it.
`400 invalid_request_error` mentioning credit	Buyer out of credit — top up, or set a USDC allowance.
Claude Code ignores your key / uses claude.ai	`ANTHROPIC_API_KEY` not blanked, or a cached login takes precedence. Set `ANTHROPIC_API_KEY=""`.
High cost per turn	Claude Code's system prompt is large; the default models are big. Use a cheaper main model and a cheap small/fast model.

Anthropic Agent SDK

The same env vars work for the Anthropic Agent SDK / @anthropic-ai/sdk — set baseURL to https://api.surplusintelligence.ai/anthropic and the API key to your inf_… key. The SDK's x-api-key header is accepted.