Barefoot shepherds competing in buildings
“That the slave-girl will give birth to her mistress and master, that you will find barefooted, destitute goat-herds vying with one another in the construction of magnificent buildings.”Sahih Muslim 8, English translation as given on sunnah.com
What happened
Within a lifetime of the oil discoveries, the Arabian Peninsula went from a largely pastoral economy to some of the highest buildings in the world, including the Burj Khalifa in Dubai (828 m, 2010).
The Muslim case
Yaqeen Institute and InfoIslam present this as a sign visible today. InfoIslam notes that the Arabic yatatawalun describes competition, each outdoing the other in height. IslamQA lists it among the signs.
Scope
The hadith speaks of competing in tall buildings; it does not say 'the tallest in the world'. It is offered as a strong correspondence with today's Gulf, not as the only possible fulfillment.