What: Nearly two-thirds of US physicians now rely on OpenEvidence's ad-funded AI chatbot for diagnosis and treatment, raising questions over accuracy and dependence as OpenAI and Anthropic push into healthcare.

Why it is important: Vertical AI products are defending their position against OpenAI and Anthropic through usage and curated sources, while the AI Act has already cost OpenEvidence access to the EU and UK.

OpenEvidence, a Miami-based start-up founded by Daniel Nadler in 2022, says nearly two-thirds of US doctors use its AI search engine, which processed more than 42mn prompts last month. Physicians query medical journals and clinical guidelines through a focused source list that includes the New England Journal of Medicine and the Journal of the American Medical Association. The ad-powered platform grew largely by word of mouth and has attracted nearly $1bn in investment over 18 months, including $250mn in September at a $15bn valuation. It is on track to generate between $400mn and $500mn in advertising by the end of 2026, according to a person close to the company.

Evidence on performance is mixed. A study by the Mayo Clinic, an investor in the start-up, found accurate recommendations in all five sampled cases, whereas a June Nature paper found it underperformed Gemini and GPT on clinical benchmarks. Concerns also centre on over-reliance by junior doctors. The company withdrew from the EU and UK over the AI Act, faces competition from OpenAI and Anthropic, and plans clinical trials and drug discovery.

IADS Notes:  The ad-funded model behind OpenEvidence, projected to generate $400mn to $500mn in advertising in 2026, echoes a shift already visible in retail, where UK online retail media rose 32% to £2bn in the first half of 2026, the fastest growth of any digital advertising category (Internet Retailing, October 2026). The same revenue logic is exposed once an AI assistant sits between audience and advertiser: AI shopping assistants threaten the advertising and commission profits of marketplaces by taking over purchase decisions, and department stores building retail media face the same exposure (a16z, September 2026). Inside ChatGPT and Claude, brands write their own content, while the platform sets the container, the ranking and the conversation (Journal du Net, September 2026). OpenEvidence's withdrawal from the EU and UK over the AI Act also has a retail counterpart in the debate on AI-generated advertising, where Eurocommerce is urging the EU to exempt non-misleading AI-generated retail ads from the Act's disclosure rules (Reuters, June 2026).

The $15bn AI start-up changing how American doctors treat patients