x402 is an HTTP payment protocol. An unpaid request returns HTTP 402 with a payment offer; sign one offer and retry the same request with proof of payment.

Do I need an account?

No account or API key is needed for these x402 calls.

Base or Solana, paid in USDC. This page focuses on Base.

Claude Opus 5.5: pay per request with x402

Call Claude Opus 5.5 with no account or API key. Pay per request in USDC on Base via x402. Price: $2.19908/1M input, $10.9954/1M output tokens.

Pay per request

Send a request to ask.singitai.app, get HTTP 402 with the exact price, pay in USDC on Base, get the answer. No signup, no monthly plan.

Provider: Anthropic · Context window: 1,000,000 tokens · Tags: vision, reasoning

Price

USD per 1M tokens	Input	Output
SingIt price (expected, markup included)	$2.19908	$10.9954
List price of the model (for reference)	$4	$20

The expected price is based on what answers from this model have cost us. It is an expected price, not a guarantee; you pay what each answer actually used.

Price = what the provider charges for the answer + 30% markup + a settlement fee per request ($0.001 on Base, $0.002 on Solana).

Per request, reference request

One short message, max_tokens 800 (30 characters), 12 input tokens. upto settles actual usage, so a real answer normally costs less; exact is flat, with no refund.

Network	upto ceiling (USD)	exact flat price (USD)
Base	$0.005422	$0.002841
Solana	$0.006422	$0.003841

Recommended: upto. Pay Claude Opus with upto: it settles what the answer really cost (+30% + the fee), up to the ceiling you sign. exact is a flat price that includes room for Opus's thinking tokens, so it is usually dearer than the answer used, with no metering and no refund.

Prices as of 2026-10-30 10:03:34 UTC (snapshot of ask.singitai.app/v1/models and /pricing.json). Live: /v1/models and /pricing.json. Live values are authoritative and the 402 response states the exact price.

Call it with x402

curl -i https://ask.singitai.app/v1/chat/completions \
  -H 'Content-Type: application/json' \
  -d '{"model":"claude-opus-5.5","max_tokens":200,"messages":[{"role":"user","content":"Hello"}]}'

The unpaid POST returns HTTP 402 and a PAYMENT-REQUIRED header: base64 JSON, x402 v2. Sign one offer (upto first, then exact; Base then Solana) and retry the same request with the PAYMENT-SIGNATURE header. HTTP 200 returns choices[0].message.content and billing.totalAtomic.

Follow the first paid call walkthrough, developer guide and llms.txt.

For a free try, use the separate model free/deepseek-v4.1-flash: 20 answers a day, no wallet. This is a different model from the one on this page.

Use it from an agent

MCP: https://app.singitai.app/mcp. Free tools without a key: list_models, get_price, list_price_symbols.

The elizaOS plugin @singitai/plugin-singit has a paid-chat action that pays on Base. Its per-call and per-day caps are held in the plugin's memory: in-process, reset on restart, not on-chain, not enforced by SingIt's servers. It does not use AgentAllowance.

Give your agent a budget

Agent spending limits for USDC on Base · How to limit what an AI agent can spend · x402 payments with a budget for AI agents

Related models

All model pages

FAQ

What is x402?: x402 is an HTTP payment protocol. An unpaid request returns HTTP 402 with a payment offer; sign one offer and retry the same request with proof of payment.
Do I need an account?: No account or API key is needed for these x402 calls.
Which network? Base?: Base or Solana, paid in USDC. This page focuses on Base.