It was during Peroz's reign—in c. 262—that the Sasanian King of Kings Shapur I (r. 240–270) carved the Ka'ba-ye Zartosht inscription.
On the inscription, Shapur I proclaimed himself as the suzerain of several regions, including that of the Kushano-Sasanians:
...I, the Mazda-worshipping lord, Shapur, king of kings of Iran and An-Iran… (I) am the Master of the Domain of Iran (Ērānšahr) and possess the territory of Pars, Parthia… Hindestan, the Domain of the Kushan up to the limits of Peshawar and up to Kash, Sogdia, and Chachestan.

Nevertheless, according to Rezakhani, the Kushano-Sasanians appear to have been too strong to have been plainly Sasanian governors, and their existence "may well reflect an early Sasanian continuation of the Arsacid imperial setting, acting as an allied, but autonomous, cadet branch of the Sasanian royal house".
According to the historian Richard Payne, "the Kushano–Sasanian sub-kingdom ruled from Balkh on behalf of the Sasanian kings of kings".
In 275, Peroz was succeeded by Hormizd I Kushanshah, a son of the King of Kings Bahram I (r. 271–274).
It was during Peroz's reign—in c. 262—that the Sasanian King of Kings Shapur I (r. 240–270) carved the Ka'ba-ye Zartosht inscription. On the inscription, Shapur I proclaimed himself as the suzerain of several regions, including that of the Kushano-Sasanians:
...I, the Mazda-worshipping lord, Shapur, king of kings of Iran and An-Iran… (I) am the Master of the Domain of Iran (Ērānšahr) and possess the territory of Pars, Parthia… Hindestan, the Domain of the Kushan up to the limits of Peshawar and up to Kash, Sogdia, and Chachestan.
Nevertheless, according to Rezakhani, the Kushano-Sasanians appear to have been too strong to have been plainly Sasanian governors, and their existence "may well reflect an early Sasanian continuation of the Arsacid imperial setting, acting as an allied, but autonomous, cadet branch of the Sasanian royal house". According to the historian Richard Payne, "the Kushano–Sasanian sub-kingdom ruled from Balkh on behalf of the Sasanian kings of kings". In 275, Peroz was succeeded by Hormizd I Kushanshah, a son of the King of Kings Bahram I (r. 271–274).
Peroz I Kushanshah