NBER has no single official methodology—multiple papers use different approaches.
The prominent recent one (Karger et al., WP 35046, Apr 2026) relies on expert elicitation surveys across economists, AI pros, and forecasters. They provide unconditional GDP growth forecasts (~2.5% annualized median) and conditional on AI progress scenarios (slow/moderate/rapid by 2030).
In the rapid scenario (AI surpassing humans on most tasks), economists forecast ~3.5% GDP growth to 2050, with LFPR falling to 55% (~10M jobs lost, half attributable to AI). This is holistic expert judgment, not a GDP = C + I + G + NX decomposition. Labor displacement, consumption effects, inequality, and adoption lags are explicitly considered in the forecasts and rationales.
Acemoglu’s task-based models (e.g., WP 32487) produce more modest near-term GDP gains (~0.9–1.2% over 10 years) while modeling substitution vs. complementarity.
The ~25% higher GDP level by 2050 in rapid vs. baseline scenarios matches parts of the range you referenced. Projections do not ignore displacement or assume unchecked G/I growth.