Linea is excited to announce Alpha v2: a significant upgrade that reduces the total cost of publishing data and verifying ZK proofs on Ethereum by up to 90%.

Alpha v2 was successfully deployed to Linea Mainnet on February 13th and introduces two new features to Linea: Proof aggregation and data compression. Let’s look at each of these features in detail.

Each Linea transaction is rolled up into a batch and published to Layer 1 (L1). Previously, in Alpha v1, each batch was verified with a zkSNARK proof to validate the computational integrity of the submission. This verification process incurred a fixed gas cost of approximately 400k gas on Ethereum.

With proof aggregation, Linea can recursively prove many consecutive batches of transactions into one single final proof such that the verification cost to verify N batches is N times cheaper.

Since the upgrade, Linea has gone from one batch per proof to averaging ~30 batches per final proof, making the fixed proof verification costs on Linea 1/30th the price of Alpha v1.

The ZK proof verification costs for Linea now make up a negligible amount of the overall costs at ~0.5%.

To reconstruct Linea's state, we transmit Layer 2 (L2) transaction data to the L1 smart contract. Acknowledging the hefty L1 gas fees, primarily driven by data storage costs, we've implemented a strategic data compression approach.

The Linea prover not only validates state transitions based on L2 transactions but does so with a crucial twist - operating on a compressed input. This innovation ensures that the L2 prover accurately decompresses the input, resulting in substantial "data usage savings" on L1.

Our lossless compression algorithm – akin to gzip and deflate, two widely used data compression algorithms – efficiently encodes repeated bytes, achieving a remarkable compression ratio. During high-activity periods, such as frequent calls to a Uniswap contract, the compression ratio can soar to 15x. Furthermore, the simplicity of the decompression process ensures affordability within a SNARK circuit, aligning with the imperative of keeping computational costs low.

As part of this upgrade, Linea is also storing more data per submission. Previously publishing ~70kb data per data submission, Linea is now posting up to the near maximum for a single Ethereum transaction at 123kb.

Here is an example of the cost savings from the upgrade:

This Alpha v1 finalization transaction on Ethereum verified 146 Linea transactions in a single batch costing ~1.2M gas.

This Alpha v2 finalization transaction verified 38,396 Linea transactions across 31 batches and 8095 blocks amounting to 261 blocks per batch. Each batch costs ~2.6M gas with an additional 0.5M gas cost for the finalization.

This means that the equivalent of 261 L2 blocks for Alpha v1 would have been ~4x more expensive in L1 gas than Alpha v2

And for the data compression, Linea has gone from averaging ~150 transactions in a single batch to ~1,500 transactions. A 10x increase in the number of compressed transactions squeezed into a single batch and data submission.

Overall, these cost reductions amount to a total average of ~4x cost reduction per finalization for Alpha v2 compared to the previous version

What’s remarkable is that Linea has achieved data compression whilst continuing to publish transaction input data on Ethereum. Here is an example data submission where you can see hashes of the transaction data included as calldata:

Reducing the L1 Rollup costs for Linea allows gas fees on Linea to be reduced. Gas fees have been immediately reduced by 66% with Alpha v2 making Linea up to 1/40th cheaper than Ethereum L1 prices and making it one of the cheapest L2 rollups in the Ethereum ecosystem.

The Linea team is already preparing for EIP-4844 and the Dencun upgrade on Ethereum on March 13th. 4844 will allow Rollups like Linea to post data submissions as blobs versus calldata and Alpha v2 sets Linea on the path to leverage this new data availability solution. Whilst it is still not certain how much this will reduce costs in practice due to the creation of a new market, it is certain to reduce prices. Linea is targeting to enable the use of blobspace shortly after the upgrade to provide more cost savings to the Linea ecosystem.

To the wonderful Linean community, thank you for your support. We’re thrilled to be delivering significantly lower gas fees to our ecosystem. The community’s involvement, voice, and partnership is a cornerstone for success as we take Linea from an idea to the decentralized home of web3 where dapps thrive.

Let us know on X what you think about the upgrade!