OpenAI: GPT-5.1 Chat
GPT-5.1 Chat is a reasoning model from OpenAI released on Jan 1, 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 $1.25 per million input tokens and $10 per million output tokens. Cached input bills at $0.125, 90% less than fresh input.
It supports tool calling, structured JSON output and prompt caching.
5 providers serve it, including 302.AI, Abacus and Helicone.
- Modalities
- In / out price
- $1.25 / $10 per 1M
- Context
- 128K
- Max output
- 16K
- Released
- Jan 1, 2025
- Knowledge cutoff
- Sep 2024
- Tool calling
- Structured output
- Reasoning
- Prompt caching
- Open weights
- Free to use
GPT-5.1 Chat 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 | $1.25 / 1M tokens | |
|---|---|---|
| Output | $10 / 1M tokens | |
| Cached input (read) | $0.125 / 1M tokens | 90% off input |
GPT-5.1 Chat providers
5 providers serve it, including 302.AI, Abacus and Helicone. Each host sets its own price and limits, so the cheapest one is not always the one with the longest context.
| Provider | Input /M | Output /M | Cache read /M | Context | Max output |
|---|---|---|---|---|---|
| 302.AI | $1.25 | $10 | – | 128K | 16K |
| Abacus | $1.25 | $10 | – | 400K | 128K |
| Helicone | $1.25 | $10 | $0.125 | 128K | 16K |
| Merge Gateway | $1.25 | $10 | $0.125 | 128K | 16K |
| OrcaRouter | $1.25 | $10 | $0.125 | 128K | 16K |
What GPT-5.1 Chat 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 Chat through an OpenAI compatible API.
- Tools
tools - Structured outputs
structured_outputs - Reasoning
reasoning
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GPT-5.1 Chat questions
How much does the GPT-5.1 Chat API cost?
$1.25 per million input tokens and $10 per million output tokens, with cached input at $0.125. The estimator on this page turns that into a monthly bill for your own workload.
What is the context window of GPT-5.1 Chat?
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.
Which providers serve GPT-5.1 Chat?
5 providers serve it, including 302.AI, Abacus and Helicone. Prices differ by host, so the Providers table on this page lists each one with its input and output price.
Does GPT-5.1 Chat support tool calling?
Yes. It accepts tool definitions and can return JSON that matches a schema, which is what an agent needs to call your APIs.
Is GPT-5.1 Chat 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 Chat released?
Jan 1, 2025, with training data up to Sep 2024.
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 Chat?
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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