OpenAI: GPT-5.1 Codex Max API
OpenAI's premier agentic coding model released in November 2025. It is the first to natively support "Compaction" technology, enabling it to operate across multiple context windows and process millions of tokens without losing critical coherence. Specifically optimized for Windows development and large-scale refactoring, it features superior self-healing and multi-step planning capabilities.
- Context window: 400,000 tokens
- Max output: 128,000 tokens
- Input: text, image
- Output: text
- Reasoning: Supported
- Tool calling: Supported
- File input: Supported
- Released: 2025-11-19
- Knowledge cutoff: 2024-09-30
Frequently Asked Questions
What is the context window of GPT-5.1 Codex Max?
GPT-5.1 Codex Max supports a context window of up to 400,000 tokens.
Does GPT-5.1 Codex Max support function calling?
Yes. GPT-5.1 Codex Max supports tool / function calling.
Does GPT-5.1 Codex Max support reasoning?
Yes. GPT-5.1 Codex Max is a reasoning-capable model.
What is the knowledge cutoff of GPT-5.1 Codex Max?
The knowledge cutoff of GPT-5.1 Codex Max is 2024-09-30.