We reserve the o3 API for our hardest reasoning steps — nothing else matches the depth. The 5% RouterBase discount is pure margin.
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The o3 API is OpenAI's most capable o-series reasoning model — a 200K-token context window, high-depth reasoning effort, vision (text + image input), function calling, and structured JSON outputs, built for the hardest math, coding, and science problems. The OpenAI o3 API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to o3. Input at $1.20 / 1M tokens, output at $4.80 / 1M tokens, cache reads at $0.30 / 1M tokens — 5% below the standard rate, all through one REST endpoint.
Input
OpenAI o3
Hi! I'm a helpful AI assistant. What can I do for you?
OpenAI o3 API: Chat
Use the o3 API to run OpenAI's flagship o-series reasoning model — deep math, coding, science, and visual reasoning with a 200K-token context.
The o3 API is OpenAI's most capable o-series reasoning model — a 200K-token context window, high-depth reasoning effort, vision (text + image input), function calling, and structured JSON outputs, built for the hardest math, coding, science, and multi-step problems. Routed through RouterBase, the OpenAI o3 API is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to o3, and your first call goes through immediately.
Pricing is $1.20 / 1M input tokens, $4.80 / 1M output tokens, and $0.30 / 1M cached-input reads — 5% below the standard rate. One RouterBase key — no separate OpenAI credentials required.
Six reasons teams ship on the o3 API
From flagship o-series reasoning to 5%-off pricing — what makes the OpenAI o3 API stand out.
Flagship reasoning depth
The o3 API runs OpenAI's deepest o-series chain-of-thought reasoning — the model you reach for on the hardest math, coding, and science problems.
Adjustable reasoning effort
Set reasoning effort on the o3 API — turn it up for maximum rigor on multi-step problems or down to balance latency and cost.
200K-token context
Accepts up to 200,000 tokens per request — long documents, multi-file code, or extended chat history fit in a single o3 API call.
Vision & function calling
The o3 API accepts images alongside text and returns structured tool calls — reason over diagrams and screenshots, define tools, and request strictly valid JSON.
OpenAI-compatible endpoint
The OpenAI o3 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 o3 API also routes to GPT-5, Claude Opus 4.8, Gemini 3.5 Flash, and 200+ other models — no per-provider credential management.
Quickstart
Get started with the o3 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 o3 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 o3. 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 o3 API
Real production loads running on the o3 API and the RouterBase model catalog.
Vision reasoning on the o3 API works through our toughest diagrams and screenshots — one call analyzes the image and returns structured results.
Structured JSON outputs from the o3 API killed our flaky regex parsing. Strictly valid JSON every time, zero retries.
When a problem needs real multi-step reasoning, the o3 API solves it. RouterBase makes it 5% cheaper and routes around outages automatically.
The o3 API handles the reasoning steps my agent loop used to fail on. One base-URL swap and I was live.
RouterBase puts the o3 API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
We A/B the o3 API against o4-mini per request — same SDK, one model field. The hard cases stay on o3 and everything else gets cheaper.
We migrated 42 services to the o3 API over a weekend. The only PR comment was 'wait, that's all?'.
At $1.20 / 1M input minus 5%, the o3 API gave us flagship reasoning without the flagship bill. The ROI math was instant.
Frequently Asked Questions
Common questions about the o3 API.
It is RouterBase's pass-through to OpenAI's o3 — the flagship o-series reasoning endpoint with a 200K-token context, high-depth reasoning effort, vision input, function calling, and structured outputs, served via an OpenAI-compatible REST interface.