Polygon Readies ZK Rollup Testnet, Eyes Mainnet Launch in 2023

At the Ethereum Community Conference (EthCC) in Paris on Tuesday, Ethereum scaling tool Polygon announced Polygon zkEVM, which the company described as a "major leap forward" in the world of zero-knowledge (ZK) technology.

In a press release, Polygon said zkEVM would be the “first Ethereum-equivalent scaling solution that works seamlessly with all existing smart contracts, developer tools and wallets, harnessing advanced cryptography called zero-knowledge proofs.”

Ethereum’s transaction capacity (around 15 transactions per second) is lower than rival blockchains like Solana and Tezos, and its high gas fees have rendered it prohibitively expensive for a variety of use cases (think $40 currency exchange fees).

Rollups like Polygon zkEVM are the main way the Ethereum community is working to boost the network’s capabilities – allowing users to transact quickly and cheaply without compromising the network’s most essential security guarantees.

There are two main types of rollups: Optimistic and zero knowledge. Of the two, zero knowledge is generally considered the superior technology, but its engineering complexity has caused it to lag behind quicker-to-market Optimistic rollups.

Read more: Ethereum’s Rollups Aren’t All Built the Same

The idea of a fully featured ZK rollup – one that can accommodate any Ethereum smart contract like the current leading Optimistic rollups – was, until recently, thought to be years away.

“Everybody thought [a zkEVM] was at least 12 to 18 months away,” Polygon co-founder Sandeep Nailwal told CoinDesk. "But here we are, and we are open sourcing the code and making the test net live.”

According to Polygon, the zkEVM test net will launch sometime this summer. A mainnet launch is expected "early 2023."

ZK rollups are powered by so-called circuits – code that can “prove” a statement is true by looking at a bite-sized, encrypted version of it.

Clever ZK circuitry enables large quantities of layer 2 transactions to get bundled up and passed down to a layer 1 chain. Instead of looking at a bunch of transactions one by one, a ZK circuit (code that lives in an Ethereum smart contract) can look at a relatively tiny blob of encoded data to confirm that transactions haven’t been spoofed or altered.

“Generally, until now, it was only possible or feasible to build these use case-specific circuits, Nailwal explained. “For example, a payment [platform], or NFT (non-fungible token) swaps – all these small individual things.”

As a result, Nailwal said, “Current ZK rollups are all restricted in the kind of smart contracts they can provide for.”

This all changes with zkEVMs – ZK rollups that can support all of the same smart contracts as Ethereum’s mainnet.

“A zkEVM is a generic circuit on Ethereum. That means you … can write custom smart contracts the same way you can write them on Ethereum – anything and everything that you want to [program].”

In other words, developers will be able to move virtually any Ethereum smart contract onto Polygon zkEVM without needing to alter its code.

Nailwal said he expects Polygon zkEVM to slice transaction fees by 90% in comparison with Ethereum. He also estimated that the network will be able to support 40 to 50 transactions per second, compared with Ethereum’s approximately 15 transactions per second. Over time, Nailwal said, the team’s Plonky 2 technology – which it announced in January – will be used to boost transaction capacity orders of magnitudes higher.

In Nailwal’s telling, zkEVMs will mark an across-the-board improvement over Optimistic rollups like Arbitrum and Optimism – the incumbent Ethereum rollup chains that were released last year and have a combined $1 billon in value locked according to DefiLlama.

For now, though, Polygon zkEVM will share one of the major shortcomings of other rollups in that it has a centralized “sequencer,” which means a single party is responsible for bundling up and ordering the layer 2 transactions that get passed down to the layer 1 blockchain.

Polygon says it is working to decentralize this element of its process. For now, though, a dishonest sequencer could theoretically pause a rollup or strategically reorder transactions in order to squeeze some extra profit for himself. If he goes offline, a sequencer can also bring the whole chain down.

But even with these risks, a centralized sequencer is unable to falsify transactions, meaning rollups still hold security advantages relative to other, more centralized scaling products.

Until now, Polygon’s main product offering has been Polygon PoS (proof-of-stake), a blockchain that can support Ethereum-compatible transactions for extremely low fees.

Users can easily swap many assets back and forth between Polygon PoS and Ethereum’s mainnet, and the company has positioned it as a way to scale the Ethereum network by serving as an off-ramp for certain kinds of activity. The chain – which is the largest network oriented around scaling Ethereum – has nearly $2 billion in total value locked, according to DefiLlama.

But Polygon PoS is unlike a rollup in that it doesn't borrow Ethereum’s security guarantees. For that reason – and despite some confusion to the contrary – it’s not considered a true “layer 2” network like Polygon zkEVM will be, and its low fees come at the cost of a more centralized security model.

Polygon zkEVM will have higher fees than the company’s PoS chain for the foreseeable future. That means the PoS chain will still be superior for use cases like gaming, which demand the lowest fees possible.

But Nailwal emphasized to CoinDesk that ZK technology is the future, and he says there may be a point at which Polygon manages to retrofit its ZK technology to its PoS chain.

The latest product announcement comes nearly a year after Polygon paid $250 million to merge with Hermez, a company focused on ZK technology that laid the groundwork for much of what ultimately became Polygon zkEVM. According to Nailwal, Polygon committed nearly $1 billion to ZK-related initiatives last year.

But Polygon’s ZK advancements don't exist in a vacuum. Other projects, like Scroll and Matter Labs (the team behind zkSync), are racing to launch their own zkEVMs at some point in the near future.

Polygon issued several tweets this week hinting that a major zkEVM-related announcement would be coming. Polygon’s MATIC token – the native gas token for Polygon’s PoS chain and its upcoming zkEVM chain – is up over 70% in the past seven days.

UPDATE (July 20, 17:23 UTC): Polygon has corrected the launch timeline that it originally provided to CoinDesk in an interview. The network will launch as a test net this summer, not this week as originally stated. The mainnet launch is expected to follow early next year, not in four to ten weeks.