GPT-4o API is our default for production assistants — the balance of intelligence and speed is exactly right. The 5% RouterBase discount is pure margin.
The GPT-4o API is OpenAI's flagship multimodal model — a 128K-token context window, vision (text + image input), function calling, and structured JSON outputs, tuned for strong general intelligence at real-time speed. The GPT-4o API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to gpt-4o. Input at $1.50 / 1M tokens, output at $6.00 / 1M tokens, cache reads at $0.75 / 1M tokens — 5% below the standard rate, all through one REST endpoint.
Input
GPT-4o
Hi! I'm a helpful AI assistant. What can I do for you?
GPT-4o API: Chat
Use the GPT-4o API to run OpenAI's flagship multimodal model — text and vision, a 128K-token context window, function calling, and structured outputs.
The GPT-4o API is OpenAI's versatile flagship "omni" model — multimodal (text + image input), a 128K-token context window, function calling, and structured JSON outputs, tuned for strong general intelligence at real-time speed. Routed through RouterBase, it is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to gpt-4o, and your first call goes through immediately.
Pricing is $1.50 / 1M input tokens, $6.00 / 1M output tokens, and $0.75 / 1M cached-input reads — 5% below the standard rate. One RouterBase key — no separate OpenAI credentials required.
Six reasons teams ship on the GPT-4o API
From multimodal vision to 5%-off pricing — what makes GPT-4o the default flagship.
128K-token context
Accepts up to 128,000 tokens per request — long documents, multi-file code, or extended chat history fit in a single GPT-4o API call.
Multimodal vision
The GPT-4o API accepts images alongside text. Pass an image URL or base64 in the same request to caption, extract, or reason over visual content.
Flagship general intelligence
GPT-4o is OpenAI's balanced flagship — strong reasoning, coding, and writing at real-time speed, the reliable default for production assistants and agents.
Function calling & JSON
Define tools and request a JSON schema; the GPT-4o API returns structured tool calls and strictly valid JSON for reliable agent and extraction pipelines.
OpenAI-compatible endpoint
The GPT-4o 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-4o 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 GPT-4o 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-4o 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-4o. The response follows the standard chat-completions schema — streaming and vision 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-4o API
Real production loads running on the GPT-4o API and the RouterBase model catalog.
Vision on the GPT-4o API replaced a separate OCR step — one call captions, extracts, and reasons over text and image together.
Structured JSON outputs from the GPT-4o API killed our flaky regex parsing. Strictly valid JSON every time, zero retries.
GPT-4o handles our multimodal pipeline end to end. RouterBase makes it 5% cheaper and routes around outages automatically.
Function calling on the GPT-4o API wires straight into my agent loop. One base-URL swap and I was live.
RouterBase puts the GPT-4o API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
We A/B the GPT-4o API against GPT-4o mini per request — same SDK, one model field. Quality stays on 4o where it counts and the bill still dropped.
We migrated 42 services to the GPT-4o API over a weekend. The only PR comment was 'wait, that's all?'.
At $1.50 / 1M input minus 5%, the GPT-4o API gave us flagship quality without the flagship bill. The ROI math was instant.
Frequently Asked Questions
Common questions about the GPT-4o API.
It is RouterBase's pass-through to OpenAI's GPT-4o — the flagship multimodal chat endpoint with a 128K-token context, vision input, function calling, and structured outputs, served via an OpenAI-compatible REST interface.