[ETCM]

The 40-floor tower which will house 1,000 prisoners will be located on the grounds of the former Manhattan Detention Complex.

1,000 inmates is not a large prison, and certainly not a "Mega-Prison". Rikers Island holds 15,000 inmates, and is a far larger site. It might be the tallest, but nowhere near the world's largest. It's not even close the New York's largest.

[Jonty30]

The article says it’s the world’s largest supermax. I don’t know the capacity for other supermax prisons in the US. I understand other supermax prisons are not necessarily stand alone buildings, but this one is. Maybe that’s the difference.