How Does a Proof-of-Stake (PoS) Network’s Equivalent of a 51% Attack Differ from PoW?

The PoS equivalent is often called a "majority stake attack" or "34% attack" (in some models). Instead of controlling 51% of the hashrate, the attacker must control a majority of the staked cryptocurrency.

The primary difference is the cost and consequence: in PoS, the attacker risks having their staked coins "slashed" or destroyed as a penalty for malicious behavior, an economic disincentive not present in PoW hashrate rental.