GPT-5.1 Codex
Summary
GPT-5.1 Codex is a proprietary language model from OpenAI, released on 13 Nov 2025. It accepts text and images and generates text, with a 400K-token context window and up to 128K output tokens per response. As of 4 Oct 2026, the lowest listed API price is $1.25 per million input tokens and $10 per million output tokens (Azure AI Foundry), across 3 providers we track.
Codex GPT for repository edits, code review, and practical software agents
Last verified 4 Oct 2026. Every figure on this page links to its source.
Specifications
| Developer | OpenAI |
|---|---|
| Release date | 13 Nov 2025 [models.dev] |
| Status | Generally available [models.dev] |
| Weights | Proprietary (API only) [models.dev] |
| Context window | 400K (400,000 tokens) [models.dev] |
| Max output | 128K tokens [models.dev] |
| Knowledge cutoff | 30 Sept 2024 [models.dev] |
| Input | Text and images [models.dev] |
| Output | Text [models.dev] |
| Reasoning mode | Yes [models.dev] |
| Tool calling | Yes [models.dev] |
| Structured output | Yes [models.dev] |
GPT-5.1 Codex API pricing by provider
USD per million tokens. Sorted by input price.
| Provider | Input | Output | Cached input | Context | Source |
|---|---|---|---|---|---|
| Azure AI Foundry gpt-5.1-codex | $1.25 | $10 | $0.13 | 400K | models.dev, 4 Oct 2026 |
| OpenRouter openai/gpt-5.1-codex | $1.25 | $10 | $0.13 | 400K | OpenRouter, 4 Oct 2026 |
| Vercel AI Gateway openai/gpt-5.1-codex | $1.25 | $10 | $0.13 | 400K | models.dev, 4 Oct 2026 |
Frequently asked questions
What is the context window of GPT-5.1 Codex?
GPT-5.1 Codex has a context window of 400,000 tokens (400K) and can generate up to 128,000 tokens in a single response, according to models.dev.
How much does the GPT-5.1 Codex API cost?
GPT-5.1 Codex is listed from $1.25 per million input tokens and $10 per million output tokens (Azure AI Foundry). Prices last verified 4 Oct 2026.
Is GPT-5.1 Codex open source?
No. GPT-5.1 Codex is a proprietary model; OpenAI has not released its weights. It is available through APIs including Azure AI Foundry, OpenRouter, Vercel AI Gateway.
When was GPT-5.1 Codex released?
OpenAI released GPT-5.1 Codex on 13 Nov 2025, according to models.dev.
Which providers offer GPT-5.1 Codex?
We track GPT-5.1 Codex on 3 providers: Azure AI Foundry, OpenRouter, Vercel AI Gateway.
Change history
No changes detected since we started tracking this model. We re-check every source daily.
Sources
- https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml
- https://github.com/sst/models.dev/blob/dev/providers/azure/models/gpt-5.1-codex.toml
- https://openrouter.ai/openai/gpt-5.1-codex
- https://github.com/sst/models.dev/blob/dev/providers/vercel/models/openai/gpt-5.1-codex.toml