NBER Working Paper W35290: Wharton Economists Find $380B AI Capex Implies 2.7× Productivity Boom Required — GDP Outcome Range Spans 5 to 58 Points by 2030

An NBER working paper (W35290) by Wharton economists Jessica and Jonathan Wachter, surfacing on r/ArtificialInteligence, embeds observed AI capital expenditures in a two-sector economic model: the five largest US tech firms spent $380 billion on capex in 2025 and are forecast to spend roughly double that in 2026, implying a sector productivity gain of approximately 2.7× is needed to justify current investment levels. Calibrated GDP growth by 2030 ranges from 5 to 58 percentage points depending on risk assumptions — a spread the authors say reflects 'substantial risk' rather than a clean bull case, and the paper is being widely cited on Hacker News and Reddit as a rare academic stress test of the AI capex narrative.