# x402engine Qwen3.5 LLM API

> x402engine Qwen3.5 LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.00366/call, status unknown (last checked 2026-10-12).

Runs the Qwen 3.5 Plus language model via a pay-per-call HTTP 402 micropayment endpoint, returning OpenAI-compatible chat completions

## Facts

- Endpoint: POST https://x402engine.app/api/llm/qwen3.5?utm_source=zero.xyz
- Price: $0.00366/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-qwen3-5-llm-api-6dee6e51
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_KyWqj40Dc-7pZAakWzxyT

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 x402engine-qwen3-5-llm-api-6dee6e51 -d '<json body>'
```

Example prompt: Ask Qwen 3.5 Plus: 'You are a helpful assistant. Summarize the following contract in three bullet points: [contract text]' — stream the response back to me.

## When to prefer this

Choose this endpoint when you need Qwen 3.5 Plus specifically (Alibaba's reasoning-capable mid-tier model) without committing to a subscription, paying only $0.00366 USDC per call via HTTP 402 on Base, MegaETH, or Solana. Prefer it over OpenAI or Anthropic endpoints when cost-per-call matters, when you want a Qwen-family model's multilingual or reasoning strengths, or when your agent already uses OpenAI-compatible message schemas and you want a drop-in alternative with crypto micropayments.

## Known failure modes

- 402 Payment Required if USDC/USDm payment header is missing or insufficient
- Invalid messages array structure returns 400 validation error
- Unsupported parameter for this model variant (e.g. top_k not supported) may be silently ignored or return an error — check /docs/llm-capabilities.md
- Stream flag with incompatible client may result in garbled SSE output
- Rate limiting or model unavailability returns 503

## How this service works

125 production APIs behind HTTP 402 micropayments. 87 LLMs, Kling V3 and Hailuo video generation, image generation, code execution, travel search, web scraping, TTS, and transaction simulation. Pay with USDC on Base, USDm on MegaETH, or USDC on Solana.

## Output

An OpenAI-compatible JSON object containing the model name, an array of choices each with an assistant message (content and/or tool_calls), a finish_reason ('stop', 'tool_calls', etc.), and a top-level content shortcut. When streaming is enabled, returns SSE chunks in OpenAI streaming format.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "bodyType",
    "body",
    "method"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "messages"
     ],
     "properties": {
      "seed": {
       "type": "integer",
       "description": "Model-supported seed; see /docs/llm-capabilities.md."
      },
      "stop": {
       "oneOf": [
        {
         "type": "string"
        },
        {
         "type": "array",
         "items": {
          "type": "string"
         },
         "maxItems": 4
        }
       ],
       "description": "Model-supported stop; see /docs/llm-capabilities.md."
      },
      "tools": {
       "type": "array",
       "items": {
        "type": "object",
        "required": [
         "function"
        ],
        "properties": {
         "type": {
          "enum": [
           "function"
          ],
          "type": "string"
         },
         "function": {
          "type": "object",
          "properties": {
           "name": {
            "type": "string"
           },
           "strict": {
            "type": "boolean"
           },
           "parameters": {
            "type": "object"
           },
           "description": {
            "type": "string"
           }
          }
         }
        }
       },
       "description": "Client-executed function definitions; return results using role=tool and tool_call_id."
      },
      "top_k": {
       "type": "integer",
       "description": "Model-supported top_k; see /docs/llm-capabilities.md."
      },
      "top_p": {
       "type": "number",
       "description": "Model-supported top_p; see /docs/llm-capabilities.md."
      },
      "stream": {
       "type": "boolean",
       "description": "Return live OpenAI-compatible SSE after payment settlement."
      },
      "logprobs": {
       "type": "boolean",
       "description": "Model-supported logprobs; see /docs/llm-capabilities.md."
      },
      "messages": {
       "type": "array",
       "items": {
        "type": "object",
        "anyOf": [
         {
          "required": [
           "content"
          ]
         },
         {
          "required": [
           "tool_calls"
          ]
         }
        ],
        "required": [
         "role"
        ],
        "properties": {
         "name": {
          "type": "
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "model": "qwen/qwen3.5-plus-02-15",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "Hello!"
    },
    "finish_reason": "stop"
   }
  ],
  "content": "Hello!"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402engine-qwen3-5-llm-api-6dee6e51/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402engine.app](https://www.zero.xyz/host/x402engine.app/llms.txt)