How are the hostels in IIIT-Delhi? How's the first years' hostel different from the rest, if there is? What differences exist between the single rooms and the twin-sharing rooms?

IIIT Delhi hostels are newly built, and well constructed. They are clean and have all the facilities. 

The hostels have all-weather ACs and good Wi-Fi connectivity. You’ll get 300 Mbps dual link, 802.11n routers, great bandwidth, and ethernet links. The washrooms are very clean.

There is no separate hostel for freshers. You’ll be sharing a common hostel with your seniors. Senior students are given preference for single rooms. For hostel allotment, students from other states are given first preference.

Boys’ hostel has double seater, while girls’ hostel has triple seater sharing rooms. Sharing rooms are slightly bigger than single seater rooms. But all rooms have the same furnishing. Each student gets a bed, a study table, one almirah, and a few drawers.

You need not worry about hostel facilities at IIIT Delhi as they are top notch.