As of my knowledge cutoff in early April 2025, OpenAI's latest flagship model is **GPT-4o** (with its various updates), though they also released **o1** and **o3** as part of their reasoning-focused model line. The **GPT-4.5** model (sometimes referred to as a research preview) was also announced around that time.

Since the AI landscape changes rapidly, I'd recommend checking OpenAI's official website for their most current flagship model, as newer releases may have occurred after my knowledge cutoff.
