Crypto Gloss

Across Protocol

Across Protocol is an intent-based cross-chain bridge that delivers near-instant transfers (2–30 seconds) and low fees by using professional relayers who front funds to users immediately while the canonical settlement proof finalizes in the background — secured by UMA Protocol’s optimistic oracle and governed by the ACX token.

Background: Why Traditional Bridges Are Slow

Traditional bridges (early Stargate, Hop, Connext) work approximately like:

  1. User locks assets in smart contract on source chain
  2. Oracle/relayer observes the lock event
  3. (Wait for finality on source chain)
  4. Oracle/relayer unlocks assets on destination chain
  5. (Wait for oracle confirmation on destination)

Problems:

  • Steps 3–5 require multiple finality windows: 15 minutes to hours for L1 bridges; 1–7 minutes for L2 bridges
  • Each liquidity pool maintains separate reserves on each chain → capital fragmentation
  • Complex multi-chain liquidity management creates MEV and imbalance risks

Across’s Architecture: Intent-Based Bridging

The protocol is built around the following components.

Relayer Model

Across uses a “relayer marketplace” — professional market makers who front funds immediately:

User flow:

  1. User requests bridge: “Send 1 ETH from Arbitrum → Base”
  2. Relayer sees the intent on Arbitrum (order includes: fee offer + expiry)
  3. Relayer sends 0.999 ETH (fee deducted) to user on Base within ~5 seconds
  4. User’s 1 ETH on Arbitrum is deposited to the Across Hub Pool
  5. Periodically (every 15–30 minutes), a “canonical bundler” verifies relayer claims and reimburses relayers from the Hub Pool with profit

From user’s perspective: Near-instant bridge with low fees

From relayer’s perspective: Risk-free arbitrage — they’re overcollateralized by the user’s deposit; the optimistic oracle just needs to confirm the deposit exists before reimbursement

Hub-and-Spoke Model

Unlike bridges with liquidity pools on every chain, Across uses a single Hub Pool (on Ethereum mainnet):

  • Hub Pool: Single canonical pool of USDC, ETH, WBTC on Ethereum
  • Spoke Pools: Lightweight deposit pools on each supported L2 (Arbitrum, Optimism, Base, etc.)
  • Capital flow: User deposits to Spoke Pool → Relayer fronts funds → Bundler settles claims → Hub reimburses relayer

Why this is capital-efficient: One pool serves all chains; no need to maintain $100M on each chain — the relayer float covers instant settlement.

Optimistic Oracle Security (UMA)

Across is secured by UMA Protocol’s Optimistic Oracle:

  • Bundler submits a “root bundle” claiming: “These relayers serviced these requests; pay them back”
  • A 30-minute challenge window allows anyone to dispute incorrect claims
  • If undisputed, root bundle is finalized and relayers reimbursed
  • If disputed → UMA’s decentralized voting system resolves the dispute

Security model: Anyone providing false claim risks having their stake slashed; only economically rational actors participate (relayers who actually fulfilled requests)

ACX Token

Symbol: ACX

Function: Governance token for Across DAO

Distribution strategy: Community-focused; LP incentives for Hub Pool liquidity providers; retroactive airdrop to early users

Protocol revenue flow:

  • Bridge fees (paid by users): ~0.05–0.1% of bridged amount
  • Revenue goes to Hub Pool LPs (liquidity providers) as yield
  • ACX stakers/governance influences fee parameters and protocol upgrades

ERC-7683: Cross-Chain Intents Standard

Across co-authored ERC-7683 (the Cross-Chain Intents Standard) with Uniswap Labs — a pivotal contribution to DeFi infrastructure:

What ERC-7683 does:

  • Standardizes how “intents” (user requests to perform cross-chain actions) are specified
  • Any intent protocol (Across, UniswapX, 1inch Fusion) can use the same format
  • Fillers (solvers/relayers) monitor for intents in standard format across all protocols
  • Creates a competitive marketplace of liquidity providers for cross-chain execution

Why this matters: Without a standard, each bridge implements its own intent format → relayers must integrate each separately. With ERC-7683, a relayer built for Uniswap’s intents automatically works for Across’s intents and vice versa → better competition → lower fees for users.

Adoption: Uniswap X, Hop, deBridge, and others implementing ERC-7683 support

Comparison: Across vs. Other Bridges

Feature Across Stargate V2 LayerZero Wormhole
Architecture Intent/relayer Liquidity pools Message passing Message passing
Speed 2–30 sec 10–60 sec 1–10 min (destination confirmation) 5–30 min
Capital efficiency High (hub-spoke) Low (per-chain pools) N/A (messaging only) N/A (messaging only)
Security model UMA optimistic oracle LayerZero DVN DVN network Guardian network
Token ACX STG ZRO W
Best use case Token bridging Stablecoin liquidity General messaging Wide chain coverage

History

  • 2021 — Across Protocol launches from within Risk Labs (the organization behind UMA Protocol). Initial focus on Ethereum-to-Optimism bridging.
  • November 2022 — ACX token launch and retroactive airdrop distributed to early bridge users and UMA stakers. Positive reception for community-first distribution.
  • 2023 — Multi-chain expansion. Base, Arbitrum, Polygon, and other chains added. Volume grows as DeFi aggregators adopt Across for cross-chain routing.
  • 2024 — ERC-7683 co-authored with Uniswap Labs. The Cross-Chain Intents Standard positions Across as core DeFi infrastructure.
  • 2025 — Across becomes the preferred bridge for DeFi aggregators. ERC-7683 adoption accelerates; Across bridges significant volume via protocol integrations.

Common Misconceptions

“Across’s optimistic oracle is less secure than ZK bridges.”

UMA’s optimistic oracle has operated without a successful attack since launch. The 30-minute challenge window and economic slashing for false claims create strong security guarantees. ZK bridges offer different security tradeoffs, not categorically better ones.

“You need ACX tokens to use Across.”

ACX is a governance token. Any user can bridge using Across without holding ACX.

Social Media Sentiment

  • r/CryptoCurrency / r/ethfinance: Across is praised by DeFi power users for speed and low fees. The ACX airdrop was well-received. ERC-7683 co-authorship with Uniswap is cited as significant validation.
  • X/Twitter: Respected in DeFi technical communities. The UMA oracle occasionally draws FUD from users unfamiliar with optimistic security models. Marketing presence is smaller than LayerZero or Wormhole despite strong technical performance.
  • Discord (Across community): Active relayer and liquidity provider community. Discussions center on Hub Pool yields, ERC-7683 integrations, and new chain deployments.

Last updated: 2026-04

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