OpenAI

OpenAI's GPT-4o architecture utilizes a decoder-only transformer with a hybrid reasoning mode that internally switches between fast pattern-matching chains and extended chain-of-thought verification. The o3-mini represents a distillation approach where a larger reasoning model's inference process is compressed into a smaller, faster model through supervised fine-tuning on reasoning trajectories. Their multimodal pipeline natively processes text, image, and audio tokens through a unified encoder rather than separate modality encoders, reducing cross-modal latency. The API surface includes structured outputs, function calling, and vision inputs, making it the most feature-complete production API. Their safety infrastructure includes automated red-teaming pipelines and constitutional AI alignment that runs as a post-training refinement layer before model release.