# GPT-5.1 Codex

> 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.

Source page: https://www.aimodel.directory/models/gpt-5-1-codex
Last verified: 4 Oct 2026

## Specifications

- **Developer:** OpenAI
- **Release date:** 13 Nov 2025 (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Status:** Generally available (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Weights:** Proprietary (API only) (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Context window:** 400K (400,000 tokens) (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Max output:** 128K tokens (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Knowledge cutoff:** 30 Sept 2024 (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Input:** Text and images (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Output:** Text (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Reasoning mode:** Yes (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Tool calling:** Yes (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)
- **Structured output:** Yes (source: models.dev, https://github.com/sst/models.dev/blob/dev/providers/openrouter/models/openai/gpt-5.1-codex.toml)

## API pricing (USD per 1M tokens)

| Provider | Input | Output | Cached input | Context |
|---|---|---|---|---|
| Azure AI Foundry | $1.25 | $10 | $0.13 | 400K |
| OpenRouter | $1.25 | $10 | $0.13 | 400K |
| Vercel AI Gateway | $1.25 | $10 | $0.13 | 400K |

## FAQ

### 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.

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Data licensed CC BY 4.0. Cite as: AI Model Directory, "GPT-5.1 Codex", https://www.aimodel.directory/models/gpt-5-1-codex