8T is the high-end of the McKinsey estimate that is 4-8T, by 20230. That includes non-AI data-centre IT, AI data-centre, and power infrastructure build out, also including real estate for data centres. Not all of it would be debt. Google, Meta, Microsoft and AWS have massive profit to fund their build outs. Power infrastructure will be funded by govts and tax dollars.
There is mounting evidence that even places like Meta are increasing their leverage (debt load) to fund this scale out. They're also starting to do accounting tricks like longer depreciation for assets which degrade quickly, such as GPUs (all the big clouds increasing their hardware depreciation from 2-3-4 years to 6), which makes their financial numbers look better but might not mean that all that hardware is still usable at production levels 6 years from now.
They're all starting to strain under all this AI pressure, even with their mega profits.