First of all, I have to say the current overview page of rollups on L2beat is incredible. So much information presented in such a great way. Congratulations.
Optimistic Rollups don’t actually work in practice - As we know Optimistic Rollups (ORUs) are a layer-2 scaling solution for Ethereum that operate on the optimistic assumption that bundled transactions are valid. To maintain trust in this decentralized system, they use mechanisms like economic bonds and a challenge period to catch and prove faults.
However, traditional methods of proving faults can be computationally expensive - there is a reason Optimism still isn’t live with fault proofs. The only system currently in production is Arbitrum, which I wuld describe as Interactive Fault Proof via Single Step Replay.
ZK Fault Proofs - There is a new game in town that projects are calling “ZK Fault Proofs” that aim to make this verification process more efficient. By using Zero-Knowledge proofs, these methods aim to prove transaction validity or fault with a minimal computational footprint, streamlining the process while maintaining system integrity. You can check projects like: Eclipse, Fuel, LayerN, Morphism to see what its about.
Now here is where the “ZK Rollup” term comes into being super misleading.
There are now two different types of rollups that use ZK tech - you could call the pessimistic (always prove validity) and optimistic (prove only when challenged) - but they both utilize zk proofs!
This is going to create a LOT of confusion.
However, I think we can frontrun this problem as a community and come up with naming that works and actually makes sense. Does anyone have a suggestions?
For sake of starting a discussion, I would actually change the whole terminology upside down. It never was about “Optimistic vs ZK”. The antonyms actually are:
Pessimistic / Optimistic
Fraud Proof / Validity Proof
“Settlement” on Ethereum: Primarily / Secondary / None
ZK Sync: Pessimistic Validity Proof Rollup that settles on Ethereum
Eclipse SVM: Optimistic Fraud Proof Rollup that settles on Celestia, and secondarily on Ethereum
But obviously this is too technical for most people to use on platforms like Twitter/X.
Morphism, one of the projects doing this new technology is calling them:
Responsive Validity Proofs
Maybe thats the best term?
While Eclipse uses Celestia for DA, it settles (only) on Ethereum, since that’s the where the canonical bridge lives, which holds special significance for the protocol. For example, the rollup’s gas token (ETH) comes from that canonical bridge, and Eclipse full nodes watch the bridge for relevant events. Agree with the rest though.
I agree that ZK rollup is confusing, but for a different reason: the “zk” property of proofs is often not used. Therefore, what it has been often proposed is using the term “Validity Rollup”, since as you said, they prove validity for each bridge update.
The term Pessimistic Rollup is unfortunately already used with a different meaning, see  and .
Okay, so how about
Optimistic Validity Rollup
Seems like a pretty simple and succinct way of going forward?