The GPT-5 API is our default for everything that has to be right the first time — frontier reasoning, no compromises. The 5% RouterBase discount is pure margin.
The GPT-5 API is OpenAI's most capable frontier 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 API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to gpt-5. Input at $0.75 / 1M tokens, output at $6.00 / 1M tokens, cache reads at $0.075 / 1M tokens — 5% below the standard rate, all through one REST endpoint.
Input
GPT-5
Hi! I'm a helpful AI assistant. What can I do for you?
GPT-5 API: Chat
Use the GPT-5 API to run OpenAI's flagship frontier model — top-tier reasoning, coding, and agentic workflows with a 400K-token context window.
The GPT-5 API is OpenAI's most capable frontier 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 API is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to gpt-5, and your first call goes through immediately.
Pricing is $0.75 / 1M input tokens, $6.00 / 1M output tokens, and $0.075 / 1M cached-input reads — 5% below the standard rate. One RouterBase key — no separate OpenAI credentials required.
Six reasons teams ship on the GPT-5 API
From frontier reasoning to 5%-off pricing — what makes the GPT-5 API stand out.
Frontier intelligence
GPT-5 is OpenAI's flagship — best-in-class reasoning, coding, writing, and agentic performance, the model teams reach for on their hardest problems.
Adjustable reasoning effort
Set reasoning effort on the GPT-5 API — turn it up for maximum rigor on multi-step problems or down to balance latency and cost.
400K-token context
Accepts up to 400,000 tokens per request — entire codebases, long document chains, or extended chat history fit in a single GPT-5 API call without chunking.
Vision & function calling
The GPT-5 API accepts images alongside text and returns structured tool calls — pass an image URL or base64, define tools, and request strictly valid JSON.
OpenAI-compatible endpoint
The GPT-5 API speaks the OpenAI chat-completions wire format. Any Python, Node, Go, or Rust SDK that works with OpenAI works here — just update the base URL.
One key for 200+ models
The same RouterBase key that calls the GPT-5 API also routes to Claude Opus 4.8, Gemini 3.5 Flash, Sora 2, and 200+ other models — no per-provider credential management.
Quickstart
Get started with the GPT-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 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. The response follows the standard chat-completions schema — streaming, reasoning, and vision supported.
Inspect usage
Every response includes a detailed token breakdown — input, output, reasoning, 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 API
Real production loads running on the GPT-5 API and the RouterBase model catalog.
Vision reasoning on the GPT-5 API reads our toughest diagrams and screenshots — one call analyzes the image and returns structured results.
Structured JSON outputs from the GPT-5 API killed our flaky regex parsing. Strictly valid JSON every time, zero retries.
When a task needs real multi-step reasoning, the GPT-5 API solves it. RouterBase makes it 5% cheaper and routes around outages automatically.
The GPT-5 API handles the coding and reasoning steps my agent loop used to fail on. One base-URL swap and I was live.
RouterBase puts the GPT-5 API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
We A/B the GPT-5 API against GPT-5 nano per request — same SDK, one model field. The hard cases stay on GPT-5 and everything else gets cheaper.
We migrated 42 services to the GPT-5 API over a weekend. The only PR comment was 'wait, that's all?'.
At $0.75 / 1M input minus 5%, the GPT-5 API gave us frontier intelligence without the frontier bill. The ROI math was instant.
Frequently Asked Questions
Common questions about the GPT-5 API.
It is RouterBase's pass-through to OpenAI's GPT-5 — the flagship frontier chat endpoint with a 400K-token context, adjustable reasoning effort, vision input, function calling, and structured outputs, served via an OpenAI-compatible REST interface.