The GPT-5.5 API is our default for the hard problems — strong reasoning, ships multi-file PRs that pass review. The 5% RouterBase discount is pure margin.
The GPT-5.5 API is OpenAI's advanced GPT-5-series model — a 400K-token context window, adjustable reasoning effort, vision (text + image input), function calling, and structured JSON outputs, built for the hardest reasoning, coding, and agentic tasks. The GPT-5.5 API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to gpt-5-5. Input at $4.75 / 1M tokens, output at $28.50 / 1M tokens, cache reads at $0.475 / 1M tokens — 5% below the standard rate, all through one REST endpoint.
Input
GPT-5.5
Hi! I'm a helpful AI assistant. What can I do for you?
GPT-5.5 API: Chat
Use the GPT-5.5 API to run OpenAI's advanced GPT-5-series model — a 400K-token context, adjustable reasoning, vision, and function calling.
The GPT-5.5 API is OpenAI's advanced GPT-5-series model — a 400K-token context window, adjustable reasoning effort, vision (text + image input), function calling, and structured JSON outputs, built for the hardest reasoning, coding, and agentic tasks. Routed through RouterBase, the GPT-5.5 API is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to gpt-5-5, and your first call goes through immediately.
Pricing is $4.75 / 1M input tokens, $28.50 / 1M output tokens, and $0.475 / 1M cached-input reads — 5% below the standard rate. One RouterBase key — no OpenAI account required.
Six reasons teams ship on the GPT-5.5 API
From advanced reasoning to 5%-off pricing — what makes the GPT-5.5 API stand out.
Advanced reasoning
The GPT-5.5 API delivers strong step-by-step reasoning for the hardest problems — adjust the reasoning effort per request to trade depth against speed and cost.
Built for coding & agents
The GPT-5.5 API handles multi-file refactors, long tool-use chains, and complex agentic workflows — a dependable backbone for production coding agents.
400K-token context
Accepts up to 400,000 tokens per request — long documents, multi-file codebases, or full conversation history fit in a single GPT-5.5 API call without chunking.
Vision & function calling
The GPT-5.5 API accepts text and image input and returns structured tool calls plus strictly valid JSON — ideal for extraction, analysis, and agent pipelines.
OpenAI-compatible endpoint
The GPT-5.5 API speaks the OpenAI chat-completions wire format. Point any OpenAI SDK at RouterBase — no separate credentials or call-site changes needed.
One key for 200+ models
The same RouterBase key that calls the GPT-5.5 API also routes to GPT-5, Claude Opus 4.8, Gemini 3.1 Pro, and 200+ other models — no per-provider credential management.
Quickstart
Get started with the GPT-5.5 API in 3 steps
From sign-up to your first response in under 5 minutes.
Create a RouterBase API key
Sign up and generate an API key — one key reaches the GPT-5.5 API and every other model in the catalog.
Send your first message
Point any OpenAI-compatible SDK at routerbase.com/v1 and set the model to gpt-5-5. The response follows the standard chat-completions schema — streaming and tool use supported.
Inspect usage
Every response includes a detailed token breakdown — input, output, and cache-read tokens — so cost and cache-hit rate are visible on every call.
Pay only for what you use
RouterBase passes through partner-tier pricing. Compared against the model's official published API rate.
What teams build with the GPT-5.5 API
Real production loads running on the GPT-5.5 API and the RouterBase model catalog.
We run our agent backbone on the GPT-5.5 API and it sustains long tool-use chains without drifting across dozens of steps.
Structured JSON outputs from the GPT-5.5 API killed our flaky regex parsing. Strictly valid JSON every time, zero retries.
Adjustable reasoning on the GPT-5.5 API lets us dial depth against cost per task. RouterBase makes it 5% cheaper and routes around outages automatically.
400K of context means I can drop a whole repo in. The GPT-5.5 API reasons across files without losing the thread.
RouterBase puts the GPT-5.5 API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
We A/B the GPT-5.5 API against GPT-5 per request — same SDK, one model field. Hard jobs go to 5.5 and easy ones stay cheap.
We routed our toughest tasks to the GPT-5.5 API over a weekend. The only PR comment was 'wait, that's all?'.
At $4.75 / 1M input minus 5%, the GPT-5.5 API gave us frontier-grade reasoning at a price we could ship. The ROI math was instant.
Frequently Asked Questions
Common questions about the GPT-5.5 API.
It is RouterBase's pass-through to OpenAI's GPT-5.5 — an advanced GPT-5-series model with a 400K-token context, adjustable reasoning effort, vision, function calling, and structured outputs, served via an OpenAI-compatible REST interface.