OpenAI is pushing stronger medical reasoning into the free ChatGPT tier: GPT-5.5 Instant now matches frontier Thinking models on its health evaluations, while 230 million users ask health and wellness questions each week.
OpenAI says GPT-5.5 Instant has pushed health responses close to its frontier Thinking models while reaching free ChatGPT users. The bigger signal is production data: flagged factuality issues in health answers fell 71% over two months.
OpenAI replaced ChatGPT's default model with GPT-5.5 Instant on May 5, 2026. The upgrade delivers 52.5% fewer hallucinations and 30% more concise responses than GPT-5.3 Instant, with new memory source controls for personalization transparency.
GPT-5.5 Instant is now ChatGPT's default model, replacing GPT-5.3 Instant. The update cuts hallucinated claims by 52.5% on high-stakes medical, legal, and financial prompts, and adds Gmail-based personalization and memory-source transparency.
Sam Altman announced the rollout of GPT-5.5-Cyber, a frontier AI model purpose-built for cybersecurity. Initial access is limited to critical cyber defenders, with broader access to follow as trusted frameworks are established.
The UK's AI Safety Institute (AISI) found that GPT-5.5 completed a multi-step corporate network attack simulation in 11 minutes at $1.73 — a task estimated to take a human expert 12 hours. It is the second model after Anthropic's Claude Mythos to reach this benchmark, confirming that advanced AI cyber capabilities are an industry-wide trend.
Hacker News liked the joke, but the real draw was OpenAI showing how a playful reward signal inside the Nerdy personality leaked creature metaphors into GPT-5.x behavior.
OpenAI’s April 27 move matters because federal AI adoption is usually constrained by procurement and compliance before it is constrained by model quality. FedRAMP 20x Moderate gives ChatGPT Enterprise and the API a government-ready path, with GPT-5.5 already included.
This matters because it gives a fast third-party read on GPT-5.5 beyond launch-day marketing. Arena says GPT-5.5 landed at #2 in Search Arena, #5 in Expert Arena, and #9 in Code Arena with a 50-point gain over GPT-5.4.
OpenAI is pitching GPT-5.5 as more than a routine model refresh. With 82.7% on Terminal-Bench 2.0, 58.6% on SWE-Bench Pro, and a claim that it keeps GPT-5.4-level latency, the company is resetting expectations for long-running coding agents.
OpenAI is attaching cash to the hardest kind of safety failure: a single prompt that breaks all five of its bio safeguards. The new GPT-5.5 Bio Bug Bounty pays $25,000 for a universal jailbreak, limits testing to GPT-5.5 in Codex Desktop, and starts formal testing on April 28.