Introducing the Model Spec

Sharing the latest Model Spec

How a Frontier Model Gets Built, Read from the Kimi K3 Report

An open, 2. 8-trillion-parameter model shipped with 47 pages of its own recipe.

Inside our approach to the Model Spec

Learn how OpenAI’s Model Spec serves as a public framework for model behavior, balancing safety, user freedom, and accountability as AI systems advance.

Introducing improvements to the fine-tuning API and expanding our custom models program

We’re adding new features to help developers have more control over fine-tuning and announcing new ways to build custom models with OpenAI.

I Built 11 Models to Predict the 2026 World Cup. They Crown Four Different Champions.

A single model hands you a single answer and no sense of how much it hinges on the dozens of choices buried inside it. The post I Built 11 Models to Predict the 2026 World Cup.

GPT-2: 1.5B release

As the final model release of GPT-2’s staged release, we’re releasing the largest version (1. 5B parameters) of GPT-2 along with code and model weights to facilitate detection of outputs of GPT-2 models.