Microsoft Corp-backed startup OpenAI began the rollout of GPT-4.
It is a powerful artificial intelligence model that succeeds the technology behind the wildly popular ChatGPT.
GPT-4 is "multimodal", which means it can generate content from both image and text prompts.
GPT-3.5 takes only text prompts, whereas the latest version of the large language model can also use images as inputs to recognize objects in a picture and analyse them.
GPT-3.5 is limited to about 3,000-word responses.
The new GPT-4 can generate responses of more than 25,000 words.