Table of Contents

  1. Essential Definitions of Interoperability
    1. Token Bridges
    2. Messaging Bridges
    3. The Interoperability Stack
    4. The Monolithic Experience - Synchronous Atomic Composability
  2. Users, dApp Builders, and Chain Builders
    1. Users
    2. dApp Builders
    3. Chain Builders
  3. Interoperability So Far - The Era of Asynchrony
    1. Cosmos and IBC
    2. Fragmentation of Ethereum/EVM Interoperability
      1. LayerZero, Hyperlane, Axelar, Wormhole, Socket, Polymer and more
      2. Multi-Message Aggregation(MMA) and Messaging Standards
      3. OFTs, xERC20, NTT, ITS, Warp Routes, and more
    3. Intents and the Application Layer Abstractions
    4. Storage Proofs with Moon-Math
  4. On-going Research for Synchrony
    1. Shared Sequencers
      1. Shared Validity Sequencing - Umbra
      2. Optimism Interop Specs
      3. Polygon’s AggLayer
      4. Astria & Espresso - Shared Sequencing as a Service
      5. Based Espresso
  5. Superchain's Future
    1. Verification Layer Improvements
      1. No Changes to the Base Layer
      2. Asynchronous Composability
      3. Shared Validity Sequencing
      4. zk-Aggregation Layer
      5. Shared Sequencer Networks
      6. Based Sequencing
    2. Comparison of Potential Solutions
      1. From Users’ Lens
      2. From dApp Builders’ Lens
      3. From Chain Builders’ Lens
    3. Transport Layer Improvements
    4. Application Layer Improvements
  6. Effort vs Impact
  7. Conclusion
  8. References

As an ecosystem of chains, Superchain has the responsibility of satisfying not just the users who are looking for an ecosystem of dApps, but also the dApp builders yearning for easy access to liquidity, along with the chain builders who are looking to be closer to a existing user-base and liquidity. Interoperability affects all three of these stakeholders. With the fragmentation of liquidity, all of these stakeholders are aligned with one goal, interoperability.

In this report,

  1. We will first understand the expectations of stakeholders from an ecosystem of chains.
  2. Dive into how different ecosystems of chains have solved the interoperability problem, the trade-offs they’ve made, and what we can learn from them.
  3. We will study the EVM-based ecosystem through the lens of laissez-faire development and attempt to understand what interoperability might look like without any preset standards.
  4. We will then look into the main topic of the report, shared sequencing. It is the solution that will unite not just Superchain, but the whole of Ethereum.
  5. Finally, we’ll compare different solutions and propose different ways the Optimism Foundation can potentially achieve seamless interoperability inside the Superchain ecosystem. This may include adopting certain interop standards, modifying Superchain sequencers to enable certain features, or just backing off and letting the market solve the problem itself.

Interoperability, although a niche space inside Crypto, is broad enough to have many concepts that might be new for many people reading this report. So we would like to define a few concepts that are necessary before we dive into the existing solutions.

Essential Definitions of Interoperability🔝

Interoperability of blockchains first became prominent when Bitcoin bridged to Ethereum through the WBTC token, minted and custodied by BitGo in 2019. WBTC is a simple token transfer bridge. This is the most widely used form of interoperability that exists today. But there is another kind of interoperability that is growing in need, secure data transfer between smart contract chains. These two are the foundations of interoperability.