Y Combinator's latest Demo Day, held on a Thursday in September 2026, featured a batch of startups skewing heavily towards "deep tech" compared with previous cohorts, according to TechCrunch's regular survey of early-stage venture capitalists. Investors described the technology on show as feeling "like science fiction," though they noted valuations across the batch were more grounded than in recent quarters. TechCrunch compiled its list from startups named by at least two investors as the buzziest of the group.

Among the highlighted companies are Atomarine, which is developing nuclear-powered floating data centres at sea and claims over $4 billion in customer letters of intent; Dipole Labs, which has built optical networking hardware to reduce energy waste in AI data centres; Isengard Industries, a defence startup producing jet-powered drones locally in allied countries and already generating $10 million in revenue; Lamb Labs, which is designing inference chips with AI model weights hardcoded into silicon for efficiency; and Praxis AI, which collects real-world data to train robots. Several founders have backgrounds from institutions including MIT, Imperial College London and Oxford.