ChatGPT is experiencing record growth after releasing a new AI image generation feature, according to OpenAI boss Sam Altman.

The AI assistant has been adding 1 million new users an hour amid “biblical demand” for its GPT-4o, which is now available for free users of the app.

“The ChatGPT launch 26 months ago was one of the craziest viral moments I’d ever seen, and we added one million users in five days,” Mr Altman wrote on X on Monday. “We added one million users in the last hour.”

OpenAI said it designed the latest ChatGPT feature to be “not only beautiful, but useful”, allowing people to generate highly-detailed images, as well as logos, diagrams and imagery conveying precise meaning.

“GPT‑4o image generation excels at accurately rendering text, precisely following prompts, and leveraging 4o’s inherent knowledge base and chat context – including transforming uploaded images or using them as visual inspiration,” an OpenAI blog post stated.

“These capabilities make it easier to create exactly the image you envision, helping you communicate more effectively through visuals and advancing image generation into a practical tool with precision and power.”

One of the most popular ways to use the technology since its release has been the creation of images in the style of the Japanese animation company Studio Ghibli.

ChatGPT users shared thousands of Studio Ghibli-style images on social media, with Mr Altman revealing that the massive demand forced OpenAI to introduce limits to the number of images people can create.

“It’s super fun seeing people love images in ChatGPT,” he wrote. “But our GPUs are melting. We are going to temporarily introduce some rate limits while we work on making it more efficient.”

OpenAI announced plans to further “push the frontiers of AI research” on Monday, after closing a $40 billion funding round.

The latest financing values the ChatGPT creator at $300 billion, making it one of the world’s most valuable private companies.

In the announcement, OpenAI said ChatGPT had grown to 500 million users since launching in November 2022.