2/3rds is required for a full 51%-style attack in PoS. https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQs#what-would-the-equivalent-of-a-51-attack-again

2/3rds is required for a full 51%-style attack in PoS. https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQs#what-would-the-equivalent-of-a-51-attack-against-casper-look-like https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQs#wh... There's a lot of misinformation regarding PoS. Vlad Zamfir has spoken a lot on cartel attacks and how they're mitigated, but the biggest, and I mean bigger than biggest, argument against all of these attacks is that it's always detectable by honest nodes shy of 2/3rds attack and it defaces the value of the coin itself to attack at that volume.