Optimism: Bedrock Edition

Making Optimism mainnet future-proof with the OP Stack

Table of Contents

Introduction

Optimism Bedrock is the latest release of the Optimism Mainnet blockchain, and the first one to leverage the OP stack architecture. It marks a major milestone in the security and decentralization of Optimism Mainnet.

The OP stack is a modular rollup-based layer 2 (L2) blockchain architecture. Instantiations of the OP stack architecture are called op-chains. Bedrock is the first production deployment of an op-chain.

This paper describes the OP stack architecture in general, and how it is instantiated in Bedrock in particular. We will also call out some of the parts that can be swapped out to create different instantiations of the OP stack.

Thanks to the OP stack architecture, Bedrock is compatible with multiple clients, and forward-compatible with validity (zero-knowledge) proofs.

Rollups

A rollup is a blockchain where a special class of nodes called sequencers [1] post their transactions to a data source (aka data availability source) and post their output root to a layer 1 (L1) blockchain, which is sometimes also called settlement layer. An output root is a commitment to the L2 chain storage as well as its history. People might also refer to them via the less correct but more common term state root.

Non-sequencer nodes are called verifier nodes [2]. Verifier nodes can pull the transactions from the data source and re-execute them. They can also read the state roots from L1 and verify their validity against their local view of the L2 chain.

The Ethereum blockchain’s decentralization is second to none, and Optimism Bedrock inherits Ethereum blockchain’s economic security and finality guarantees by using it for both data availability and settlement. Other configurations of the OP stack can make other choices.

<aside> 1️⃣ Bedrock uses a single sequencer secured with a failover. Sequencer decentralization will happen in the future, and there are multiple ways to operationalize it. To remain general, we’ll talk about sequencers in the plural tense, and use the term “authorized sequencers” to refer to sequencers authorized to submit batches to the data source at some specific moment in time.

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<aside> 2️⃣ Some people also call them validators or replicas.

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Design Principles

The Bedrock op-chain architecture distinguishes itself by its design principles:

1. Modularity and upgradability — The OP stack promotes separation of concerns between components that communicate with each other through simple well-defined interfaces. As a result, it is easy to swap components in and out. The thoughtful use of versioning schemes in key interfaces makes it possible to add capabilities without altering the rollup architecture.