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x402engine Claude Opus 5.5 LLM API
x402
x402engine Claude Opus 5.5 LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.056313/call, status unknown (last checked 2026-10-12).
Provides pay-per-call access to Anthropic's Claude Opus 5.5 flagship model for advanced reasoning, coding, and long-horizon agentic tasks via HTTP 402 micropayments
Price / call$0.056313
Success—
StatusUnknown
How this service works
x402engine — Claude Opus 5.5 is Anthropic's flagship model for demanding reasoning, coding, and long-horizon agentic work, succeeding Claude Opus 5. It is particularly strong at multi-step changes in large codebases, code...
Output
Returns an OpenAI-compatible JSON response containing the assistant's generated message content, finish reason (stop, tool_calls, length, etc.), model identifier ('anthropic/claude-opus-5.5'), and choice index. Supports optional streaming via SSE for real-time token delivery. Tool call arrays are included when the model invokes client-defined functions.
Example use cases
Multi-step codebase refactoring agent
“I need Claude Opus 5.5 to go through my entire Node.js backend, find all places using the deprecated callback-style async patterns, and rewrite them using async/await — pass all the relevant files as user messages and stream the output so I can watch progress.”
Complex multi-turn reasoning task
“Have Claude Opus 5.5 work through this 50-page legal contract, identify every clause that could expose us to liability, and summarize each risk with its severity — use the full conversation history I've built up so far.”
Agentic tool-use workflow
“Run Claude Opus 5.5 with these three function definitions — search_database, send_email, and update_record — and give it the task of finding all overdue invoices and drafting follow-up emails for each one, letting it call the tools as needed.”
Technical details
Endpoint
POSThttps://x402engine.app/api/llm/claude-opus-5.5?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need Anthropic's most capable Claude model (Opus 5.5) for demanding tasks like multi-step codebase changes, complex multi-turn reasoning, or long-horizon agentic workflows, and you want pay-per-call billing via USDC micropayments without a monthly API subscription. Prefer this over cheaper Claude tiers when task complexity genuinely requires frontier-level reasoning. Use over OpenAI alternatives when Claude's coding and instruction-following strengths are preferred.
Side effects
- Insufficient USDC balance for micropayment — HTTP 402 payment required error
- Malformed messages array missing required role or content fields — 400 validation error
- Exceeding context window limits for very large codebases — token limit error
- Stream connection dropped mid-response — partial SSE output
- Tool call schema mismatch — model may hallucinate function names if definitions are ambiguous
- PDF plugin not available for unsupported file types beyond native engine
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"model": "anthropic/claude-opus-5.5",
"choices": [
{
"index": 0,
"message": {
"role": "assistant",
"content": "Hello!"
},
"finish_reason": "stop"
}
],
"content": "Hello!"
}
}Tags
x402
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