GPT-5.5 API
gpt-5-5GPT-5.5 is OpenAI’s advanced reasoning model for agentic coding, knowledge work, scientific research, and complex multi-step task execution. Served via the Responses API (`/v1/responses`) with adjustable reasoning effort (low–xhigh), web search, function calling, and multimodal input. Drop-in for OpenAI Codex CLI with wire_api = "responses".
API Documentation
View complete API reference with all parameters and examples.
Advanced Features
Streaming
Enable real-time streaming responses with Server-Sent Events.
{
"model": "gpt-5-5",
"stream": true,
"messages": [...]
}Function Calling (Tools)
Enable the model to use tools and call functions.
{
"model": "gpt-5-5",
"tools": [{
"type": "function",
"function": {
"name": "get_weather",
"description": "Get current weather for a location",
"parameters": {
"type": "object",
"properties": {
"location": {"type": "string", "description": "City name"}
},
"required": ["location"]
}
}
}],
"messages": [{"role": "user", "content": "What's the weather in Tokyo?"}]
}JSON Mode
Get structured JSON responses from the model.
{
"model": "gpt-5-5",
"response_format": {"type": "json_object"},
"messages": [{"role": "user", "content": "Extract info as JSON: John is 30 years old"}]
}API Parameters Reference
| Parameter | Type | Required | Description |
|---|---|---|---|
| model | string | Yes | Model identifier (e.g., gpt-5-5) |
| messages | array | Yes | Array of message objects with role and content |
| max_tokens | integer | No | Maximum tokens in the response |
| stream | boolean | No | Enable streaming responses (SSE) |
| temperature | number | No | Sampling temperature (0.0 - 2.0) |
| top_p | number | No | Nucleus sampling threshold (0.0 - 1.0) |
| tools | array | No | Function calling tools definition |
| response_format | object | No | Output format (e.g., json_object) |
Full API Documentation
View complete API reference with streaming, thinking, and more.
Pricing
Billing: Cost = (input_tokens * input_price + output_tokens * output_price) / 1,000,000
Top Reasoning
Frontier reasoning for agentic coding, research, and complex multi-step work
Adjustable Effort
reasoning.effort = low / medium / high / xhigh
Tools & Web Search
Built-in web search or function calling (one per request)
Cached Input
Cached input billed at $0.5 / 1M; reasoning tokens count as output
About GPT-5.5
GPT-5.5 is a Large Language Model API provided by OpenAI. GPT-5.5 is OpenAI’s advanced reasoning model for agentic coding, knowledge work, scientific research, and complex multi-step task execution. Served via the Responses API (`/v1/responses`) with adjustable reasoning effort (low–xhigh), web search, function calling, and multimodal input. Drop-in for OpenAI Codex CLI with wire_api = "responses". Through APIMODELS platform, you can access this model via a unified API with transparent pay-as-you-go pricing. Current pricing: Input: $3, Output: $18 per 1M tokens.
Key Features
- Top Reasoning -- Frontier reasoning for agentic coding, research, and complex multi-step work
- Adjustable Effort -- reasoning.effort = low / medium / high / xhigh
- Tools & Web Search -- Built-in web search or function calling (one per request)
- Cached Input -- Cached input billed at $0.5 / 1M; reasoning tokens count as output
Use Cases
Chatbot & Customer Support
Build intelligent conversational systems to automatically answer user queries and improve service efficiency.
Content Generation
Automatically write articles, emails, ad copy, and other text content to boost productivity.
Code Assistant
Assist with code writing, debugging, and code review to accelerate software development.
Data Analysis
Understand and analyze unstructured data, extract key insights, and generate summary reports.
Why APIMODELS
- Unified API -- One API key to access all models, no need to register on multiple platforms
- Transparent Pricing -- Pay-as-you-go with per-call pricing published on every model page, ideal for indie developers and startups
- Instant Access -- Start using immediately after signup, supports Stripe and Alipay payments
- Full Documentation -- Detailed API docs with code examples in cURL, Python, and Node.js
Frequently Asked Questions
How much does GPT-5.5 cost?
GPT-5.5 is available through APIMODELS at: Input: $3, Output: $18 per 1M tokens. Billing is pay-as-you-go — you only pay for what you generate.
How to use GPT-5.5 API?
Sign up at APIMODELS, get your API key, and call our unified API endpoint. We provide detailed API documentation with code examples in cURL, Python, and Node.js.
What is the difference between APIMODELS and the official OpenAI API?
APIMODELS offers the same GPT-5.5 model through our aggregation platform. We provide a unified API interface so you do not need separate accounts for each provider - one API key to access all models.
What is GPT-5.5 and what's it best at?
GPT-5.5 is a frontier reasoning model served on the OpenAI Responses API with tunable reasoning effort (low→xhigh). It excels at hard, multi-step problems and agentic coding — it is the model behind OpenAI Codex CLI when pointed at APIMODELS (wire_api = responses). Higher effort spends more reasoning tokens, billed as output.
GPT-5.5 vs GPT-5.4 — which should I pick?
GPT-5.5 is the newer, stronger tier for the hardest tasks; GPT-5.4 is more affordable and fast enough for most coding and agent work. Both run on the Responses API and work in Codex CLI — switch by changing one model name.
Does GPT-5.5 support function calling and web search?
Yes — function calling and the built-in web_search tool both work (mutually exclusive per request). Tool calls drive Codex CLI's local file and shell operations. See /docs/codex.
How does GPT-5.5 compare to other Large Language Model models?
On APIMODELS, GPT-5.5 runs alongside 60+ models on one API key and one balance, so choosing is about fit, not lock-in. It supports Agentic Coding, Deep Reasoning, Web Search, Multimodal, and you can weigh it on price and capability against other Large Language Model models, then switch by changing a single model-name string — no new account or integration. Browse every Large Language Model option with live pricing at apimodels.app/models.
What can GPT-5.5 do?
GPT-5.5 supports: Agentic Coding, Deep Reasoning, Web Search, Multimodal. See the APIMODELS docs for full parameters and call examples.
Can I access the GPT-5.5 API from anywhere (incl. China)?
Yes. APIMODELS exposes GPT-5.5 through a single unified API and one key — no separate provider accounts, and no need to handle each provider's regional network access yourself.
What payment methods are supported?
We support Stripe (Visa, Mastercard, and other international cards) and Alipay. Credits are available instantly after payment.
Related models
Related reading
How to get access, regional availability, and how this model compares with its alternatives.