# x402engine GPT-5.6 Terra Pro LLM API

> x402engine GPT-5.6 Terra Pro LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.03574/call, status unknown (last checked 2026-10-20).

Calls OpenAI's GPT-5.6 Terra Pro model via a pay-per-call HTTP 402 micropayment endpoint, supporting chat completions with tool use, streaming, and file/image inputs.

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.6-terra-pro?utm_source=zero.xyz
- Price: $0.03574/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-20
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-5-6-terra-pro-llm-api-6e0dea7b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_743lD13VCHfLtyrSNefEn

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-terra-pro-llm-api-6e0dea7b -d '<json body>'
```

Example prompt: Ask GPT-5.6 Terra Pro: 'Explain the trade-offs between transformer and state-space models in 3 paragraphs' — pay the $0.036 micropayment in USDC on Base and stream the response back to me.

## When to prefer this

Choose this endpoint when you need GPT-5.6 Terra Pro specifically — OpenAI's most capable frontier model — without managing OpenAI API keys or subscriptions. Ideal for agents that need pay-per-call billing in USDC, want OpenAI-compatible request/response format, require tool calling or file/image inputs, and want to avoid rate limit management. Prefer over other LLMs on x402engine when task complexity demands frontier-level reasoning.

## Known failure modes

- 402 Payment Required if micropayment header is missing or insufficient
- 400 Bad Request if messages array is empty or malformed
- Tool call results not provided in follow-up messages cause incomplete completions
- Seed parameter ignored if model does not support deterministic generation
- Truncated response if token limit exceeded mid-stream

## How this service works

x402engine — OpenAI's higher-compute Terra tier for demanding reasoning workloads

## Output

Returns an OpenAI-compatible chat completion JSON object containing the model name ('openai/gpt-5.6-terra-pro'), a choices array with the assistant message, finish reason, and optionally tool_calls or reasoning fields. If streaming is enabled, returns SSE events in OpenAI 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."
      },
      "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-terra-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-terra-pro-llm-api-6e0dea7b/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)