We route 90% of our traffic through the GPT-5 nano API — reasoning-grade classification and extraction at a fraction of the cost. The 5% RouterBase discount is pure margin.
The GPT-5 nano API is OpenAI's fastest and cheapest GPT-5 model — a 400K-token context window, adjustable reasoning, vision (text + image input), function calling, and structured JSON outputs, tuned for low latency and high throughput. The GPT-5 nano API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to gpt-5-nano. Input at $0.03 / 1M tokens, output at $0.24 / 1M tokens, cache reads at $0.003 / 1M tokens — 5% below the standard rate, all through one REST endpoint.
Input
GPT-5 nano
Hi! I'm a helpful AI assistant. What can I do for you?
GPT-5 nano API: Chat
Use the GPT-5 nano API to run OpenAI's fastest, cheapest GPT-5 model — reasoning, a 400K-token context window, and vision.
The GPT-5 nano API is OpenAI's smallest and most cost-efficient GPT-5 model — a 400K-token context window, vision (text + image input), adjustable reasoning effort, function calling, and structured JSON outputs, tuned for low latency and high throughput. Routed through RouterBase, it is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to gpt-5-nano, and your first call goes through immediately.
Pricing is $0.03 / 1M input tokens, $0.24 / 1M output tokens, and $0.003 / 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 nano API
From a 400K-token context to 5%-off pricing — what makes GPT-5 nano stand out.
400K-token context
Accepts up to 400,000 tokens per request — long documents, multi-file code, or extended chat history fit in a single GPT-5 nano API call.
Reasoning at nano cost
The GPT-5 nano API exposes adjustable reasoning effort — dial it up for harder problems or down for speed, all at the cheapest tier in the GPT-5 family.
Fastest, cheapest GPT-5 tier
Built for high-volume workloads: the GPT-5 nano API is the lowest-cost GPT-5 model at $0.03 / 1M input tokens — ideal for classification, autocomplete, extraction, and routing at scale.
Vision & function calling
The GPT-5 nano 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 nano 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 nano 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-5 nano 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 nano 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-nano. 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 nano API
Real production loads running on the GPT-5 nano API and the RouterBase model catalog.
Vision on the GPT-5 nano API replaced an OCR pipeline — one fast, cheap call captions and extracts, text and image together.
Structured JSON outputs from the GPT-5 nano API killed our flaky regex parsing. Strictly valid JSON every time, zero retries.
At our volume, GPT-5 nano is the only GPT-5-class model that pencils out. RouterBase makes it 5% cheaper still.
Adjustable reasoning on the GPT-5 nano API lets me dial cost against quality per request. Cheap enough that I stopped counting tokens.
RouterBase puts the GPT-5 nano API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
We A/B the GPT-5 nano API against GPT-5 per request — same SDK, one model field. Most traffic stays on nano and the bill dropped 70%.
We migrated 42 services to the GPT-5 nano API over a weekend. The only PR comment was 'wait, that's all?'.
At $0.03 / 1M input minus 5%, the GPT-5 nano API made our high-volume features actually profitable. The ROI math was instant.
Frequently Asked Questions
Common questions about the GPT-5 nano API.
It is RouterBase's pass-through to OpenAI's GPT-5 nano — the fastest, cheapest GPT-5-family chat endpoint with a 400K-token context, adjustable reasoning, vision input, function calling, and structured outputs, served via an OpenAI-compatible REST interface.