My timeline splits at the rack envelope: frontier AI training halls turn liquid-ready by default around 2028, new builds above 50-100 kW/rack adopt it as baseline by ~2030, and air-only becomes a niche exception at megawatt scale by ~2035. Meanwhile the installed base — 75% perimeter air, 22% direct liquid — keeps its fans for years. Merchant silicon cements the split: AMD's latest accelerator ships liquid-only, its 2026 rack fully liquid; NVIDIA's next generation matches the no-air option. The mandate is real, but only for the frontier, on a dated schedule.