I. Introduction 4

II. Background 6

III. Methods 8

IV. Data 11

V. Relative Income Dynamics: A First Look 12

VI. Proximate Determinants: Capital, Human Capital, and Productivity 15

VII. Decomposing Relative Productivity: Efficiency versus Workforce Composition 18

VIII. Human Capital and Productivity Mobility: An Estimated Capability Threshold 20

IX. AI as Skill Augmentation and Diffusion 24

X. Long-Run Projections: Convergence under Alternative Mobility Regimes 27

XI. Robustness, Stability, and Interpretation 29

XII. Conclusion 32

References 34

Appendix A: Relative Income Dynamics 37

Appendix B: Mobility of Inputs 38

Appendix C: Productivity Mobility 40

Appendix D: Human Capital and Productivity Mobility 42

Appendix E: Development Accounting 45

Appendix F: Artificial Intelligence Counterfactuals 46