OpenAI is rolling out ‘GPT-5.5 Instant’ as the new default model inside ChatGPT, replacing GPT-5.3 Instant in a phased update starting May 2026. The updated model brings measurable gains in accuracy, including a reported drop of over 50% in hallucinated responses in sensitive domains, along with improvements in reasoning benchmarks like AIME and GPQA. It also gives shorter, faster answers and includes improved memory features for more personalized responses.
The rollout is happening gradually across ChatGPT’s global user base, meaning not everyone will see the change at once. GPT-5.5 Instant is part of the broader GPT-5.5 family, which also includes more powerful variants like GPT-5.5 and GPT-5.5 Pro. However, the ‘Instant’ version is optimized for speed and efficiency, making it suitable as the default model used by millions of people every day.
One of the biggest improvements is in reliability. OpenAI’s internal testing shows that hallucinated and made-up answers have been reduced by around 52.5% in high-risk areas like medical, legal, and financial queries. Additionally, difficult real-world conversations flagged by users now see around 37% fewer mistakes.
Performance gains are also visible in standardized benchmarks. On AIME, a challenging mathematics test, the model scores just over 80%, a significant jump from the mid-60% range seen in the previous version. On GPQA, which measures PhD-level scientific reasoning, it reaches the mid-80% range. Visual reasoning tests like CharXiv also show improvements, indicating that the model is not just better at writing but also at understanding complex problems.
Another noticeable change is how the model communicates. GPT-5.5 Instant is designed to be more concise, using about 30% fewer words and nearly 29% fewer lines in its responses. It avoids unnecessary repetition, excessive formatting, and overuse of emojis, aiming for clearer and more direct answers. This makes it more suitable for professional, academic, and productivity-focused use. Personalization has also been upgraded. The model can use memory from past conversations more effectively, reducing the need for users to repeat information. It can also connect with external data sources, including email, to provide more relevant responses. At the same time, the Sam Altman-led firm has introduced controls that allow users to view, manage, and delete stored memory.
“GPT‑5.5 Instant is rolling out starting today to all ChatGPT users, replacing GPT‑5.3 Instant as the default model, and in the API as chat-latest. For paid users, GPT‑5.3 Instant will remain available for three months, accessible through model configuration settings, before being retired,” the AI giant announced.
The update comes at a time when competition in the AI space is intensifying, with companies focusing not just on building more powerful models but also on making them safer and more reliable.
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Ashutosh is a Senior Writer at The Tech Portal, largely reporting on new tech, and intersection of technology and business. Ashutosh’s career spans across nearly a decade of technology writing across multiple platforms and languages.
