Crypto Gloss

Shared Sequencing

The Ethereum rollup ecosystem has a coordination problem. Each rollup (Arbitrum, Optimism, zkSync, Starknet) has its own sequencer — the node that decides transaction order. These sequencers are centralized (run by the rollup team) and siloed: a swap on Arbitrum and a swap on Optimism happen in isolation, with no way to atomically coordinate them. Shared sequencing addresses both problems: replace rollup-specific centralized sequencers with a shared, decentralized network that sequences transactions for multiple rollups simultaneously. This creates a foundation for atomic cross-rollup transactions (“cross-chain composability at the sequencer level”) and removes the centralization trust assumption from each rollup. Major projects building shared sequencer networks include Espresso Systems and Astria.

The Sequencer’s Role

Before diving into shared sequencing, understand what a sequencer does:

A rollup sequencer:

  1. Receives transactions from users
  2. Orders them into batches (decides which comes first)
  3. Posts the ordered batch to L1 (Ethereum) for permanent recording
  4. Provides “soft confirmation” to users immediately (before L1 posting)

The centralization problem:

  • Current rollup sequencers are single points of failure
  • If Arbitrum’s sequencer goes down → no transactions process
  • If the sequencer is malicious → it can reorder, censor, or front-run user transactions
  • Each rollup has separate sequencer infrastructure → multiple single points of failure

The composability problem:

  • DeFi composability (lego blocks) makes Ethereum powerful — protocols interact atomically
  • On a single rollup, composability works fine
  • Across two rollups, you need a bridge — no atomicity, MEV opportunities between chains, 7-day withdrawal delays
  • No existing mechanism enables “if trade on Rollup A, atomically also trade on Rollup B”

What Shared Sequencing Enables

The following sections cover this in detail.

Atomic Cross-Rollup Transactions

  • User submits a bundle: “Swap USDC for ETH on Arbitrum AND deposit ETH to Aave on Optimism”
  • Shared sequencer includes both transactions in the same “slot” across both rollups
  • Either both succeed or both fail (atomic)
  • Enables arbitrageurs, DeFi protocols, and users to compose across rollups seamlessly

Example — Cross-rollup arbitrage:

  • ETH price on Arbitrum DEX: $2,000
  • ETH price on Optimism DEX: $2,010
  • Atomic cross-rollup transaction: buy ETH on Arbitrum + sell ETH on Optimism in one bundle
  • Currently impossible to do atomically; with shared sequencing, possible with sequencer coordination

Decentralized Sequencing

  • No single entity controls transaction ordering
  • Sequencer censorship requires coordination of 2/3 of staked nodes
  • Each rollup no longer depends on its own team’s sequencer
  • Sequencer censorship resistance improves

MEV Redistribution

  • Atomic bundles create new MEV opportunities
  • Shared sequencer can auction these to searchers and distribute revenue to rollups or users
  • More transparent and controllable than each rollup having opaque MEV capture

Key Projects

The following sections cover this in detail.

Espresso Systems

  • HotShot consensus (BFT-based, built on Espresso’s research)
  • Integration with multiple rollup frameworks (OP Stack, Arbitrum Orbit, zkSync ZK Stack)
  • Espresso’s sequencer provides confirmed headers that each rollup uses for transaction ordering
  • The rollup still executes transactions itself; Espresso only orders them

Rollup partners: Multiple major rollups have discussed or begun integrating Espresso.

Astria

  • “Lazy chain” — shared sequencing without any execution state
  • Astria sequences transactions for multiple rollups simultaneously
  • Each rollup execution environment (EVM, etc.) executes its own transactions, just using Astria’s agreed ordering

SUAVE (Flashbots)

  • Not strictly a shared sequencer, but a cross-chain MEV auction and coordination network
  • Allows expression of bundles and intents across multiple chains
  • Overlaps with shared sequencing in cross-chain atomic execution goals

Based Sequencing (Alternative Approach)

Based rollups take a different approach to decentralized sequencing:

  • Instead of a separate staked sequencer network, use Ethereum L1 validators as sequencers
  • L1 validators include rollup transactions in the next L1 block
  • Sequencing is “inherited” from Ethereum consensus — as secure and decentralized as Ethereum itself
  • No new trust assumption on a separate sequencer network

Tradeoff: Based rollups have higher latency (L1 block time ~12s vs. dedicated sequencer soft confirms in <1s) but inherit maximum security.

Projects exploring based sequencing: Taiko (built-in design), and based rollup research by Justin Drake.

Challenges and Status

The following sections cover this in detail.

Technical Complexity

Economic Alignment

Status (2025)

  • Espresso has testnet infrastructure
  • No major production rollup has deployed shared sequencing in production
  • Ethereum’s “rollup-centric roadmap” implicitly encourages sequencer decentralization but doesn’t mandate it
  • Most analysts expect shared sequencing to be adopted gradually over 2025-2027

Social Media Sentiment

Shared sequencing is primarily discussed among technically sophisticated audiences — Ethereum researchers, rollup developers, and DeFi power users. The concept is widely understood to solve real problems (centralization, cross-rollup composability) but remains in research/early development stages. The main debate: “Is the complexity worth it vs. simpler solutions like intent-based bridging (like CoW Protocol cross-chain)?” The based rollup approach (using L1 validators) is seen as more elegant but with latency tradeoffs. Flashbots’ SUAVE adds another approach to the design space. Overall, shared sequencing is on the roadmap for serious Ethereum scalability advocates but hasn’t had a breakout production moment that would make it broadly discussable beyond core developers.

Last updated: 2026-04

Related Terms

Sources

Nakamoto, S. (2008). Bitcoin: A Peer-to-Peer Electronic Cash System. Bitcoin.org.

Buterin, V. (2021). An Incomplete Guide to Rollups. Vitalik.ca Blog.

Kelkar, M., Zhang, F., & Juels, A. (2020). Order-Fairness for Byzantine Consensus. CRYPTO 2020.

Drake, J. (2023). Based Rollups — Superpowers from L1 Sequencing. Ethereum Research Forum.

Babel, K., et al. (2023). Clockwork Finance: Automated Analysis of Economic Security in Smart Contracts. IEEE S&P 2023.