OpenAI: GPT-5.1 API
An upgraded version of the GPT-5 series released in November 2025. It bifurcates the model into Instant and Thinking variants, managed by an automatic routing system. GPT-5.1 offers a "warmer" and more personable tone than the original GPT-5, with significant improvements in instruction following and logical consistency for long-horizon tasks.
- Context window: 400,000 tokens
- Max output: 128,000 tokens
- Input: text, image
- Output: text
- Reasoning: Supported
- Tool calling: Supported
- File input: Supported
- Released: 2025-11-12
- Knowledge cutoff: 2024-09-30
Frequently Asked Questions
What is the context window of GPT-5.1?
GPT-5.1 supports a context window of up to 400,000 tokens.
Does GPT-5.1 support function calling?
Yes. GPT-5.1 supports tool / function calling.
Does GPT-5.1 support reasoning?
Yes. GPT-5.1 is a reasoning-capable model.
What is the knowledge cutoff of GPT-5.1?
The knowledge cutoff of GPT-5.1 is 2024-09-30.