# SingIt Ask – Anthropic Messages API

> SingIt Ask – Anthropic Messages API is a paid API for AI agents from ask.singitai.app, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-28).

Sends a prompt to Claude or any listed model via Anthropic's Messages API, paying per successful answer in USDC over x402 with no account or API key required.

## Facts

- Endpoint: POST https://ask.singitai.app/v1/messages?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-28
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/singit-ask-anthropic-messages-api-1c1f8c1d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_9qezLA2eU4ECnv1uSj2yw

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability singit-ask-anthropic-messages-api-1c1f8c1d -d '<json body>'
```

Example prompt: Ask Claude to explain the pros and cons of transformer architectures versus state space models in about three paragraphs — no API key needed, just pay per answer.

## When to prefer this

Choose this endpoint when you need Anthropic Messages API compatibility (Claude models) specifically, want to pay per successful answer rather than via subscription, and are operating in a crypto-native or x402-capable agent environment. Prefer the sibling OpenAI Responses API endpoint if you need GPT or Gemini models instead. Best for agents that lack Anthropic API credentials or need to avoid recurring billing.

## Known failure modes

- Payment not received or insufficient funds — request rejected before inference
- Model not found in /v1/models list — returns 404 or 400
- Malformed request body (missing required fields) — 422 validation error
- Upstream Anthropic API error — proxied error response with no charge
- Request too large for model context window — error with no charge
- Network timeout on slow requests — may require retry

## How this service works

SingIt Ask: Anthropic's Messages API (what Claude Code and the Anthropic SDK speak), any model listed at GET /v1/models, Claude included. Call it when an agent needs a Claude-format answer with no API key or account, or wants to try another model the same way.

## Output

Returns an Anthropic Messages API-compatible JSON response containing the assistant's generated message content, stop reason, model used, and token usage counts. Charged only when a valid answer is delivered; the charge is actual token cost plus 30% plus a small settlement fee (0.001 USDC on Base, 0.002 on Solana), up to a per-request ceiling.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "examples": [
    "claude-sonnet-5.5",
    "gpt-5.5",
    "gemini-3.1-pro"
   ],
   "maxLength": 120,
   "description": "Any model id from GET /v1/models; Anthropic's dashed names (claude-sonnet-5-5) work too."
  },
  "tools": {
   "type": "array",
   "description": "Optional Anthropic tool definitions."
  },
  "stream": {
   "enum": [
    false
   ],
   "type": "boolean",
   "description": "Streaming is not offered: an answer is paid for whole."
  },
  "system": {
   "description": "Optional system-level context for the model, as text or content blocks."
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role",
     "content"
    ],
    "properties": {
     "role": {
      "enum": [
       "user",
       "assistant"
      ],
      "type": "string"
     },
     "content": {
      "description": "Text, or a list of Anthropic content blocks."
     }
    }
   },
   "maxItems": 200,
   "minItems": 1,
   "description": "The conversation, oldest first (Anthropic format)."
  },
  "max_tokens": {
   "type": "integer",
   "maximum": 32000,
   "minimum": 1,
   "description": "The longest answer, in tokens. The payment ceiling grows with it; the charge follows what was used."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/singit-ask-anthropic-messages-api-1c1f8c1d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ask.singitai.app](https://www.zero.xyz/host/ask.singitai.app/llms.txt)