Base Layer-2: Optimism Superchains

Optimism’s modular vision of interoperable L2s built on its tech stack received a huge vote of confidence on February 23, 2023 when Coinbase announced it would be building an L2, dubbed Base. It will be an OP stack chain, and Coinbase has committed to collaborating with the core Optimism development team to help scale and decentralize Ethereum in an open source manner. This has a large impact on the how Coinbase will monetize its large user base, how the future of the Optimism ecosystem will unfold, and how Ethereum will successfully scale as it continues to embark on its rollup-centric roadmap.

Optimism’s Bedrock

Optimism’s Bedrock upgrade, scheduled to go up for vote between March 2 and April 5, is a set of open-source modular design frameworks that will power Optimism and its ecosystem of ‘Superchains.’ Bedrock enables standardized proof systems by encouraging developers to fork its codebase, cheaper transactions for L2 users, and much more robust handling of reorgs that occur on the Ethereum base layer. It also improves node performance by removing excess technical debt in prior client implementations. Bedrock also ensures the inclusion of L2 deposits in correct order, includes support for EIP-1559, and increases security assurances for L2-to-L1 withdrawals.

Cheaper transactions are supported via Bedrock due to the simplicity of the message passing design between Optimism and Ethereum, referred to as the wire format, as well as storing L2 blocks on Ethereum in a non-contract address. L2 transactions inherit the security of Ethereum by requiring sequencers to post transaction batches, or channels, to the base layer in the form of compressed calldata. These channels are broken down into frames that support parallelized batch submissions across various OP stack sequencers, minimizing the complexity of sequencer software while optimizing for the bandwidth of data availability on Ethereum. Post-Bedrock implementation, the L1 security fee should be reduced by ~20% for OP stack chains.

To improve synchronization with Ethereum, Optimism nodes will always derive blocks from the L1 after Bedrock’s implementation. As a result, if the Ethereum L1 experiences a reorg, OP stack chains will also reorg to match the state of Ethereum. Similar to Ethereum’s separation of execution and consensus clients, the OP stack separates its execution and rollup node clients as well. The execution client is a fork of Geth, the most widely used Ethereum client, with minimal changes made outside of code related to handling L2 deposits and transaction fee calculations. The rollup node, in contrast to Ethereum’s consensus clients, does not operate under a PoS consensus but instead is tasked with reading the data and deposits on the L1 using the same Engine API used by Ethereum.

In order to reduce the cost of proving any particular piece of data within an L2 block posted to Ethereum as compressed calldata, block proposers will submit output roots (or Merkle roots) to verify the state of the canonical L2 chain to the L1. In the future, there will be a bonding requirement for proposers to ensure that these output roots are accurate and posted in good faith. If a proposer posts an invalid output root, their bond will be slashed. However, the fully fleshed out fault proof mechanism is still being researched, so it will not be implemented with the Bedrock upgrade. As such, users should be aware that Optimism is currently a trusted setup.

Optimism Superchains