OpenAI announced today that its latest model, GPT-5.5 Instant, is now available to global paid users and will be fully rolled out to all free users on June 26. This upgrade marks OpenAI's largest-scale update in 2026, with GPT-5.5 Instant replacing GPT-5.3 Instant as the default model across all ChatGPT platforms, serving hundreds of millions of active users in their daily conversations. In terms of performance, GPT-5.5 Instant has reduced hallucination rates by 52.5% in high-stakes fields such as healthcare, law, and finance compared to its predecessor, with a 37.3% decrease in user-reported factual errors. In hard benchmark tests, accuracy on the AIME 2025 math competition improved from 65.4% to 81.2%, GPQA doctoral-level science questions from 78.5% to 85.6%, and MMMU-Pro multimodal reasoning from 69.2% to 76.0%. From a user experience perspective, GPT-5.5 Instant delivers more direct and structured outputs, reducing word count by approximately 30% and line count by nearly 29% for the same amount of information. It also enhances precision in image understanding, STEM problem-solving, and web search judgment, significantly improving completion rates in high-frequency scenarios. The model incorporates an intelligent routing mechanism that automatically assesses question complexity, enabling low-latency responses for simple tasks while switching to deep reasoning mode in the background for complex queries. Regarding context windows, free users get 16K, Plus and Business users receive 32K, while Pro and Enterprise users can access up to 128K.