GPT-4, released March 14, 2023, was the model that proved scaling kept working. It passed a simulated bar exam in the top 10% of test takers, accepted image input, and was so far ahead of contemporaries that it anchored ChatGPT Plus, Microsoft's Bing Chat, and the first wave of serious commercial LLM applications. Notably, Anthropic released Claude 1 the very same day.

OpenAI published almost no technical details — no parameter count, architecture, or training data — a break from research-lab tradition that set the industry's closed-frontier norm. GPT-4 headed OpenAI's lineup for more than a year, extended by GPT-4 Turbo's 128K context window in November 2023, until GPT-4o replaced it in May 2024.