OpenAI: GPT-5.1-Instant
GPT-5.1-Instant is a reasoning model from OpenAI released on Nov 12, 2025. It reads text and images and writes text, with a 128K token context window and up to 16K tokens per reply.
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It costs $1.10 per million input tokens and $9 per million output tokens. Cached input bills at $0.11, 90% less than fresh input.
It supports tool calling and prompt caching.
- Modalities
- In / out price
- $1.10 / $9 per 1M
- Context
- 128K
- Max output
- 16K
- Released
- Nov 12, 2025
- Knowledge cutoff
- n/a
- Tool calling
- Structured output
- Reasoning
- Prompt caching
- Open weights
- Free to use
GPT-5.1-Instant pricing
USD, as listed on Oct 15, 2026. Most bills are input heavy, so the cached input rate matters as much as the headline price.
| Input | $1.10 / 1M tokens | |
|---|---|---|
| Output | $9 / 1M tokens | |
| Cached input (read) | $0.11 / 1M tokens | 90% off input |
What GPT-5.1-Instant costs per month
Pick a workload close to yours or type your own volumes.
Supported request parameters
What you can set when you call GPT-5.1-Instant through an OpenAI compatible API.
- Tools
tools - Reasoning
reasoning
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GPT-5.1-Instant questions
How much does the GPT-5.1-Instant API cost?
$1.10 per million input tokens and $9 per million output tokens, with cached input at $0.11. The estimator on this page turns that into a monthly bill for your own workload.
What is the context window of GPT-5.1-Instant?
128,000 tokens of input, and it can write up to 16,384 tokens in one reply. As a rough guide, a million tokens is around 750,000 English words.
Does GPT-5.1-Instant support tool calling?
Yes. It accepts tool definitions, which is what an agent needs to call your APIs.
Is GPT-5.1-Instant open source?
No. OpenAI serves it through an API only, so you cannot download the weights or host it yourself.
When was GPT-5.1-Instant released?
Nov 12, 2025.
Catalog data from models.dev (MIT licensed), refreshed daily, last on Oct 15, 2026. The summary is written from these facts.
Building on GPT-5.1-Instant?
I test your real tasks on it and the two closest alternatives, then ship the agent on whichever wins on cost and accuracy.
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