Rollups Transition: Will All Rollups Become zk-Rollups?

The need to enhance Ethereum scalability, reduce gas fees, and increase transaction speed led to the development of layer-2 blockchains. However, there is nothing like a single infrastructure for Layer-2; what we currently have is a series of technologies implemented to create alternative and faster blockchains for users. These include Layer-2 chains (L2), sidechains, shards and more.

While Layer-2 can, therefore, be considered the future of Layer-1 blockchain, the question is, what is the future of Layer-2 chains?

Layer-3 chains or a more unified Layer-2?

Back in 2024, Vitalik Buterin made an optimistic tweet stating that all rollups will eventually move to zk-rollups. Undoubtedly, zk-rollup comes with compellable features compared to its counterpart, optimistic rollup, but the question that remains unanswered is whether zk-rollup indeed has what it takes to outperform optimistic rollup in coming years and become the rollup of choice for every developer.

Let's also not forget that optimistic rollup takes the lion's share of rollup adoption at the moment, housing leading industry players like Arbitrum and Optimism, thanks to its scalability and fast transaction throughput.
The ongoing conversation in the blockchain space signals a pending move to zk-rollup. Before we examine the whys, let's look at the core features of rollup technology.

What is rollup technology?

Rollup enhances layer-1 scalability by moving the computation component of transaction execution off-chain. It basically intercedes users' interaction with the base layer (the Layer-1 blockchain). Hence, when users perform transactions on a rollup-powered Layer-2 chain, it stores and compresses the transaction data into one summary batch. The batch is then sent to the base chain for finalization.

Of all the layer-2 chains, blockchains relying on rollup technology stand out because they are able to operate as standalone blockchains. Though built on a Layer-1 chain, L2 chains feature distinct infrastructure components that make them a blockchain of their own. From distinct consensus mechanisms to transaction approval techniques, but they rely on the base chain for data availability, censorship resistance, and security.

Types of rollups

The two types of rollups are optimistic rollups and zk-rollups. You can read more on the differences between zk-rollups and optimistic rollups in our previous post, but let's examine why everyone is saying all rollups will eventually become zk-rollups.

Why is zk-rollups better than Optimistic rollups?

Comparing zk-rollups with optimistic rollups leaves us with one ultimate differentiating feature - the use of validity-proof in zk-rollups compared to the use of fraud-proof by optimistic rollups.

For zk-rollups, validity-proof works like a pre-check system. That is, transactions are verified before finalization. When a transaction is initiated on an L2 chain, a cryptographic proof (known as zero-knowledge proof) is generated to verify the correctness of the transaction. After this, transactions are bundled up and sent to the Ethereum blockchain. At this stage, no further verification is needed.

On the other hand, optimistic rollups use a fraud-proof mechanism. It assumes that transactions are valid at the point of submission. However, before finalization, a challenge period (usually 7 days) is initiated where validators can confirm the validity of the transactions. If the transactions are valid, they are added to the block, invalid transactions are reversed, and fraudsters are penalized.

This implies that with zk-rollups, transaction submission may take longer, but finalization is instant. On the contrary, transaction submission on optimistic rollup is faster, but finalization happens after the challenge period.

It further implies that while zk-rollups rely on cryptography and high-level systems to ensure security, optimism rollup assumes that all users are honest. This approach poses a significant challenge to blockchain infrastructure. The assumption that transactions are valid and that all users are honest undermines trust minimization, which is a leading feature of blockchain technology.

Additionally, the fraud proof approach is prone to security risks and breaches, making optimistic rollups less ideal for applications and protocols with high security needs.

By providing protocols with these essential benefits, zk-rollup is considered a more decentralized and secured Layer-2 technology. Additionally, zk-rollups feature a high anonymity set and privacy by ensuring that transaction data or details are revealed to only the parties directly involved (sender and receiver). This enhances security and protects against other cryptocurrency-related risks like MEV attacks.

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Conclusion

Despite the vivid benefits of zk-rollup, it comes with specific bottlenecks that gave optimistic rollup the head start it currently enjoys. Aside from delayed submission, its cryptographical verification requires advanced hardware and high technological knowledge, making it less accessible for several validators.

However, the blockchain space is constantly evolving, making the idea that zk-rollups may overcome these bottlenecks a not farfetched truth. At the moment, we have seen the combination of Scroll and Cysic led to the introduction of a faster zk-rollup with minimal hardware configuration requirement.

But while this development is possible, it is vital also to consider that zk-rollup is only essential for protocols with high-security needs. For protocols that prioritize fast submission with low-security requirements, optimistic rollup will remain a more attractive option. Hence, while many contests that all rollups will transition to zk-rollups, we are more likely to continue to witness an ecosystem where the two rollups co-exist to satisfy different needs.

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