He isn't prime minister, but party secretary and president. Li Keqiang is premier, the closest thing to a PM, but not as powerful as a party secretary (the president position is ceremonial).
Hu Jintao served two terms as party secretary, but never consolidated his power base (Jiang Zemin protruded a lot into his reign), so was not very powerful, even compared to his premier (wen jiabao). Xi, on the other hand, has completely consolidated his power base and sidelined Li Keqiang. His competitors and apparent successors have been hit up on corruption (they are all corrupt, but who gets prosecuted depends on power plays).
If his successor (maybe another Hu) isn't apparent at this congress, then there will be a lot of talk of him staying passed his terms. If the successor is named, which is probable, then that talk will stop. However, he could totally pull a Jiang Zemin and retain some powerful poets (e.g. Head of the military commission) to keep more influence afterward. But in reality, all the retired leaders retain power behind the scenes, and it's just a matter of how much (him putting his protégés in power and kicking out Hu's will help a lot).
Hu Jintao served two terms as party secretary, but never consolidated his power base (Jiang Zemin protruded a lot into his reign), so was not very powerful, even compared to his premier (wen jiabao). Xi, on the other hand, has completely consolidated his power base and sidelined Li Keqiang. His competitors and apparent successors have been hit up on corruption (they are all corrupt, but who gets prosecuted depends on power plays).
If his successor (maybe another Hu) isn't apparent at this congress, then there will be a lot of talk of him staying passed his terms. If the successor is named, which is probable, then that talk will stop. However, he could totally pull a Jiang Zemin and retain some powerful poets (e.g. Head of the military commission) to keep more influence afterward. But in reality, all the retired leaders retain power behind the scenes, and it's just a matter of how much (him putting his protégés in power and kicking out Hu's will help a lot).