On August 7, 2025, OpenAI released GPT-5 as a unified system that “knows when to respond quickly and when to think longer,” automatically deciding whether a question needs a fast answer or extended step-by-step reasoning. That folded the separate reasoning-model track - the o-series - back into the main GPT line, so users no longer had to pick between a fast model and a slow reasoning model. The single-model, auto-routing approach became a template other providers followed. OpenAI reported 74.9 percent on SWE-bench Verified and 94.6 percent on the AIME 2025 math competition without tools.