OpenAI just made its most medically literate AI model the default for every ChatGPT user on the planet. GPT-5.5 Instant, which launched on May 5 as a replacement for GPT-5.3 Instant, now matches the company’s frontier reasoning models on health-related queries, a category where getting things wrong carries real consequences.
The numbers behind the health benchmark gains
On HealthBench, OpenAI’s internal evaluation suite for medical accuracy, GPT-5.5 Instant scored between 49.6 and 51.4 across variants. That represents a 1.8-point improvement on the overall score compared to its predecessor, with a more dramatic 5.5-point advantage on professional-grade medical queries.
The hallucination reduction is the headline stat, though. OpenAI recorded a 52.5% decrease in hallucinated claims on high-stakes prompts spanning medical, legal, and financial topics.
User-flagged factual errors also dropped by 37.3%, suggesting the improvements aren’t just visible in controlled benchmarks. Real people using the product are encountering fewer moments where the model confidently states something that simply isn’t true.
