Enlarge (credit: OpenAI) On Thursday, OpenAI announced that all paying API customers now have access to the GPT-4 API. It also introduced updates to chat-based models, announced a shift from the Completions API to the Chat Completions API, and outlined plans for deprecation of older models. Generally considered its most powerful API product, the GPT-4 API first launched in March but has been under closed testing until now.