Nebius Group stock is falling, with the reason for the decline reported as a shift in the company's AI plan that affects capital expenditures. Alternatively, the decline may be related to Meta's move to the cloud, which could negatively impact Nebius, or to the company's plan to raise debt after deals with Meta and Nvidia. The exact day of the stock fall and the extent of the decline are unclear, with different reports citing various days and percentages.