# x402engine GPT-5.6 Sol Pro LLM API

> x402engine GPT-5.6 Sol Pro LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.035735/call, status unknown (last checked 2026-10-11).

Call OpenAI's GPT-5.6 Sol Pro model via a pay-per-call HTTP 402 micropayment endpoint, paying with USDC on Solana

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.6-sol-pro?utm_source=zero.xyz
- Price: $0.035735/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-5-6-sol-pro-llm-api-fdf1d7d1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_29V0c6s4MDn31mPKbops-

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-gpt-5-6-sol-pro-llm-api-fdf1d7d1 -d '<json body>'
```

Example prompt: Send this message to GPT-5.6 Sol Pro and return the response: 'Explain the trade-offs between proof-of-work and proof-of-stake consensus mechanisms in plain English.'

## When to prefer this

Choose this endpoint when you need GPT-5.6 Sol Pro specifically, want to pay per call in USDC on Solana without an OpenAI subscription, are building an autonomous agent that self-funds inference via crypto micropayments, or need the highest-capability OpenAI model available on a usage-based basis with no monthly commitment.

## Known failure modes

- Insufficient USDC balance on Solana wallet causes HTTP 402 payment failure
- Invalid or malformed message payload returns 400 error
- Model overload or upstream OpenAI outage causes 503 or timeout
- Unsupported parameters for this model variant cause validation errors
- Network latency on Solana payment settlement adds delay

## 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

Returns a JSON object with the model name ('openai/gpt-5.6-sol-pro'), a choices array containing the assistant's message with role and content fields, a finish_reason ('stop' or similar), and a top-level content field with the response text.

## 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."
      },
      "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."
      },
      "stream": {
       "type": "boolean",
       "description": "Return live OpenAI-compatible SSE after payment settlement."
      },
      "plugins": {
       "type": "array",
       "items": {
        "type": "object",
        "required": [
         "pdf"
        ],
        "properties": {
         "id": {
          "enum": [
           "file-parser"
          ],
          "type": "string"
         },
         "pdf": {
          "type": "object",
          "properties": {
           "engine": {
            "enum": [
             "native"
            ],
            "type": "string"
           }
          }
         }
        }
       },
       "description": "Optional native PDF parser only; automatically enabled for file inputs."
      },
      "messages": {
       "type": "array",
       "items": {
        "type": "object",
        "anyOf": [
         {
          "required": [
           "content"
          ]
         },
         {
          "required": [
           "tool_calls"
          ]
         }
        ],
        "required": [
         "role"
        ],
        "properties": {
         "name": {
          "type": "string"
         },
         "role": {
          "enum": [
           "system",
   
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "model": "openai/gpt-5.6-sol-pro",
  "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-gpt-5-6-sol-pro-llm-api-fdf1d7d1/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)