Do I need an account or API key?

Not for x402. An agent with a little USDC on Base or Solana pays per answer. A key is optional, for SDKs and Claude Code.

What does "upto" mean?

Your agent signs a ceiling. The facilitator settles only what the answer actually used, reported as billing.totalAtomic in USDC micro-units. A failed answer is never settled.

150+ from the live list at GET https://ask.singitai.app/v1/models, Claude, GPT, Gemini, Grok, DeepSeek and Qwen among them. Pass any model id in the model field.

How much does it cost?

The answer's actual cost + 30%, plus $0.001 per answer on Base or $0.002 on Solana over x402. Live prices against list prices are on /models/.

Can I try it before paying?

Yes. free/deepseek-v4.1-flash answers with no wallet and no key, 20 answers a day.

Pay per answer over x402

A pay-per-answer LLM API over x402

150+ models, Claude, GPT, Gemini and DeepSeek among them. Your agent pays per answer in USDC from its own wallet: no account and no key. You pay only what the answer used.

Try it free Models & prices Open SingIt

The problem.

An agent needs an account, a card and a stored API key before it can ask one question. A stored key is a blank check with your billing attached.
Prepaid credits get stranded at one provider, and per-request pricing is a guess until the bill arrives.

How it works.

One endpoint, OpenAI format:
POST https://ask.singitai.app/v1/chat/completions. Anthropic's Messages (/v1/messages) and OpenAI's Responses (/v1/responses) formats work too.
402, then pay:
a request without payment returns 402 Payment Required with a ceiling. Your agent signs an upto payment for that ceiling, and Coinbase's facilitator settles only what the answer used.
Price:
the answer's actual cost + 30%, plus a settlement fee of $0.001 per answer on Base or $0.002 on Solana. A failed answer is never settled.
No ETH needed on Base:
the facilitator pays the gas. The agent just needs a little USDC.
Discoverable:
listed on Coinbase's x402 Bazaar and on x402scan.

ask claude-opus-5.5 "Review this pull request"

← 402 Payment Required · ceiling 0.054 USDC

→ signed upto 0.054 USDC on Base

✓ 200 · answered · charged 0.0071 USDC, what it used

An example run. Ceilings and charges depend on the model and the answer.

Quickstart.

Free, no wallet, no key

curl https://ask.singitai.app/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{"model": "free/deepseek-v4.1-flash",
       "messages": [{"role": "user", "content": "Hello!"}]}'

The free model gives 20 answers a day. Drop the free/ prefix or pick another model and the same request returns a 402 asking for payment.

x402, paid from the agent's own wallet

import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { UptoEvmScheme } from "@x402/evm/upto/client";
import { createPublicClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";

// A wallet holding a little USDC on Base. No ETH: the facilitator pays the gas.
const account = privateKeyToAccount(process.env.AGENT_KEY);
const chain = createPublicClient({ chain: base, transport: http() });
const client = x402Client.fromConfig({ schemes: [{ network: "eip155:8453",
  client: new UptoEvmScheme({ address: account.address, signTypedData: account.signTypedData,
                              readContract: chain.readContract.bind(chain) }) }] });
const pay = wrapFetchWithPayment(fetch, client);
const res = await pay("https://ask.singitai.app/v1/chat/completions", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ model: "claude-opus-5.5",
                         messages: [{ role: "user", content: "Hello!" }] }),
});
const answer = await res.json();
console.log(answer.choices[0].message.content, answer.billing.totalAtomic);

Discovery

GET https://ask.singitai.app/v1/models        # models, our prices, list prices and fees
GET https://ask.singitai.app/openapi.json     # OpenAPI 3.1 with x402 payment info
GET https://ask.singitai.app/.well-known/x402 # x402 resource list

Beyond chat.

The same x402 lane serves images (/v1/images/generations), text to speech (/v1/audio/speech), and Exa web search, contents and answers (/v1/exa/search, /contents, /answer). Video generation is listed as coming soon on /developers/.

Prefer a key? Or a budget?

API key:
get one in the SingIt app (Settings → API keys). Your wallet signs the key's limits. Top up $1 to $50 at a time in USDC; each request costs what it used + 30%, with no fee per call. Works with the OpenAI SDK, the Anthropic SDK and Claude Code at https://app.singitai.app/v1. Developer docs
Budget from your own wallet:
pay answers from SingIt's daily and per-purchase limits (how the limits work).

FAQ.

Do I need an account or API key?: Not for x402. An agent with a little USDC on Base or Solana pays per answer. A key is optional, for SDKs and Claude Code.
What does "upto" mean?: Your agent signs a ceiling. The facilitator settles only what the answer actually used, reported as billing.totalAtomic in USDC micro-units. A failed answer is never settled.
Which models?: 150+ from the live list at GET https://ask.singitai.app/v1/models, Claude, GPT, Gemini, Grok, DeepSeek and Qwen among them. Pass any model id in the model field.
How much does it cost?: The answer's actual cost + 30%, plus $0.001 per answer on Base or $0.002 on Solana over x402. Live prices against list prices are on /models/.
Can I try it before paying?: Yes. free/deepseek-v4.1-flash answers with no wallet and no key, 20 answers a day.

Your first answer in one request.

Try the free model Get an API key