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claude-opus-5-5

Latest featured Anthropic Opus model for long-running agentic coding, complex reasoning, and knowledge work.

Get API Key on gpt88.ccQuickstart

Overview

  • Claude Opus 5.5 was released on September 22, 2026 for long-running agentic coding and knowledge work.
  • The Claude API model ID is claude-opus-5-5. The model is documented with a 1M-token context window and 128k maximum output, which suits sustained planning, tool use, and quality-first workflows.
  • Adaptive thinking is always on. Use the effort parameter to control thinking depth; the documented default effort is medium.

Best Use Cases

  • Evaluate it for migrations, refactors, bug sweeps, test repair, and cross-file review in large codebases
  • Use it for long-running agents that plan across multiple steps, call tools, and recover from intermediate failures
  • Test it on long documents, structured material, and business rules that require several stages of work
  • Choose it as the latest Opus candidate when output quality matters more than minimum latency

Integration Notes

  • Use the GPT88 Base URL https://api.gpt88.cc and set model to claude-opus-5-5 in OpenAI-compatible requests.
  • Claude- or Anthropic-style tools should use the same GPT88 Base URL and send the exact model ID in their native request format.
  • Call GET /v1/models, then send a minimal POST /v1/chat/completions request before adding tools, streaming, or long context.
  • When migrating from Claude Opus 5, review the changes to thinking, tool_choice, computer use, and text returned between tool calls before enabling advanced controls.

Usage Notes

  • Availability, pricing, context and output limits, rate limits, routes, permissions, and feature support are determined by the current GPT88 console configuration and GET /v1/models.
  • This is a newly released route. Canary it on a fixed evaluation set and representative workloads before changing a production default.
  • Adaptive thinking is always on; native Claude Messages API integrations should use effort instead of legacy thinking disabled/enabled settings.
  • Keep a tested Claude Fable 5.1, Claude Opus 4.8, or other stable fallback until quality, latency, usage, and tool behavior are established.

Capabilities

1M-token context128k max outputAdaptive thinkingTool use

Recommended Scenarios

  • Long-running coding agents
  • Large codebase migrations
  • Complex knowledge work
  • Multi-tool automation

Endpoint Path

POSThttps://api.gpt88.cc/v1/chat/completions

The endpoint path is determined by the model category. Chat, image, video, and audio models use different endpoints.

Send requests with Authorization: Bearer <API_KEY>. See Chat Completions API for the full parameter reference.

API Docs

Endpoint
POST /v1/messages or POST /v1/chat/completions
Model ID
claude-opus-5-5
Content-Type
application/json
Protocol
Claude family model. Claude-native tools should prefer the Anthropic Messages protocol; OpenAI-compatible tools can use the compatibility path.
Base URL
Use https://api.gpt88.cc for Claude Code / Anthropic SDK, OpenAI SDK, Cursor, and cURL.

Headers / Auth

  • AuthorizationstringRequired
    Send Bearer <GPT88_API_KEY>. Create the API key in the gpt88.cc console.
  • Content-TypestringRequired
    Request body format. Audio transcription uploads use multipart/form-data.
    Default:application/json
  • Acceptstring
    Non-streaming requests return JSON; streaming chat requests return SSE chunks.
    Default:application/json or text/event-stream

Chat Protocol Differences

For chat models, the protocol used by the client matters as much as the model name. Claude Code / Anthropic SDK and OpenAI SDK build different request paths.

OpenAI Compatible
Base URL
https://api.gpt88.cc
Endpoint
POST /v1/chat/completions
Body
{ "model": "claude-opus-5-5", "messages": [...] }
Anthropic / ClaudeRecommended
Base URL
https://api.gpt88.cc
Endpoint
POST /v1/messages
Body
{ "model": "claude-opus-5-5", "messages": [...] }

This model is in the Claude family. Claude Code, Anthropic SDK, OpenClaw, and similar tools should prefer the Anthropic / Claude path.

Request Parameters

The fields below are generated by model category. Pricing, context limits, rate limits, and available routes should be confirmed in the gpt88.cc console.

  • modelstringRequired
    Current model ID: claude-opus-5-5. Preserve the exact casing when copying.
  • messagesarray<Message>Required
    Conversation history. Each message includes role and content.
  • streamboolean
    Enable SSE streaming. Useful for chat interfaces and long responses.
    Default:false
  • temperaturenumber
    Sampling temperature. Higher values produce more variation; production workloads usually start with a fixed value.
    Default:1
  • max_tokensinteger
    Maximum output tokens for this request. Real context limits should be confirmed in the console.
  • response_formatobject
    Structured output config, for example { "type": "json_object" }.
  • toolsarray<Tool>
    Function-calling tool definitions. Availability depends on the model and account configuration.

Response Fields

Response bodies generally follow OpenAI-compatible shapes. Media models may return async task IDs or resource URLs.

  • idstringRequired
    Unique completion ID for tracing and debugging.
  • objectstringRequired
    Usually chat.completion or a streaming chunk type.
  • modelstringRequired
    Actual model ID that handled inference.
  • choicesarray<Choice>Required
    Generated choices including message, delta, and finish_reason.
  • usageobject
    Token usage statistics. Streaming calls may return this only at the end or in non-streaming mode.

Status Codes

  • 200OKRequired
    Request succeeded. See the response field table above for the response body shape.
  • 400Bad Request
    Invalid request fields, such as missing required fields, unsupported image size format, or unsupported file type.
  • 401Unauthorized
    API key is missing, invalid, or malformed.
  • 404Not Found
    Endpoint or model not found. Confirm the path is /v1/chat/completions and the model ID is claude-opus-5-5.
  • 429Rate Limited
    Rate limit, concurrency cap, or insufficient balance. Check the console for the current allowance.
  • 5xxUpstream Error
    Upstream or request failure. Retry with the same Base URL and keep the request ID for debugging.

Errors and Troubleshooting

  • 401: verify Authorization is Bearer <API_KEY> and the key is still valid.
  • 404: confirm the endpoint is /v1/chat/completions and the model ID claude-opus-5-5 is available in the console.
  • 429: reduce concurrency, shorten requests, or check balance and quota in the console.
  • 5xx: retry with the same Base URL and keep the request ID for debugging.

Request Examples

curl https://api.gpt88.cc/v1/chat/completions \
  -H "Authorization: Bearer $GPT88_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-5-5",
    "messages": [
      {"role": "user", "content": "Introduce gpt88.cc in one sentence."}
    ]
  }'

Expected response (trimmed example):

200 OKjson
{
  "id": "chatcmpl-claude-o",
  "object": "chat.completion",
  "created": 1730000000,
  "model": "claude-opus-5-5",
  "choices": [
    {
      "index": 0,
      "finish_reason": "stop",
      "message": { "role": "assistant", "content": "..." }
    }
  ],
  "usage": { "prompt_tokens": 24, "completion_tokens": 64, "total_tokens": 88 }
}