OpenAI Announce GPT-4 will be available on April 30 from ChatGPT OpenAI says that GPT-4 was retired and completely replaced by a new native multimodal model, GPT-4o.
According to the official evaluation report, the GPT-4o surpasses the GPT-4 model across the board in the areas of writing quality, programming assistance, and STEM, and has recently been further upgraded to improve GPT-4o's instruction following, problem solving, and dialog flow.

1AI found that OpenAI officially released GPT-4 on March 14, 2023, and GPT-4 has been added to the official webpage with the message of "coming offline on April 30th".