> Can you exhaust your social security?
No, no more than you can exhaust a purchased annuity. Which is also not like an age-tested BI.
> Or is it an entitlement that you have to qualify for (credits over a number of years) and then can continue to draw until death?
Right, so, exactly not like BI, which is equal and unconditional (even excluding consideration of the influence of age, since its specifically based on the amount of contributions, adjusted by the the wage index from the time they were earned, and then adjusted by the CPI from the time benefits started being drawn.
In a sense, its more of a retrospective reverse-means-tested benefit program, which makes it about as far from BI as you can be and still be a government benefit program at all.