Across comparison is a Fast-Transfer Test Against Relayer Liquidity

Across Fast Fills Versus the Arbitrum Bridge’s Seven-Day Exit

The Arbitrum Bridge is a canonical rollup gateway, while Across is an intent bridge that pays from relayer inventory before protocol settlement completes.

An Across relayer sees the origin-chain deposit, evaluates the fee, and supplies matching assets through the destination SpokePool. The recipient therefore waits for a fill transaction, not for the origin asset to finish its canonical journey. An Arbitrum-to-Ethereum withdrawal through the Arbitrum Bridge follows the rollup’s mandatory seven-day waiting period before the claim. Across exchanges that fixed delay for a quote whose speed rests on available ETH, WETH, USDC, or another supported output token on Ethereum. The quote names the recipient and output amount, so delivery remains explicit even though the reimbursement path stays behind the interface.

The same contrast applies to the Optimism Standard Bridge. An OP Mainnet withdrawal uses three onchain stages - initiation, proof, and finalization - and its Ethereum challenge period lasts seven days. Across presents one destination output amount before deposit, then separates that user-facing fill from later relayer reimbursement. The timing difference is structural, and OP Mainnet exposes it as a seven-day boundary.

Relayer Inventory Sets the Real Instant-Fill Ceiling

Relayer inventory is working capital held on destination chains, and its available amount sets the ceiling for an immediate Across fill.

Across’s transfer-limit model exposes five fields: a minimum deposit, overall maximum, instant maximum, short-delay maximum, and recommended instant amount. Their values move with the token pair, origin chain, destination chain, relayer balances, pool utilization, and gas conditions. A route below the instant maximum fits the fastest liquidity band; one above it needs a short delay, a smaller transfer, or another route. The approval quote also reports fee details and an expiry timestamp, so a previous response doesn’t establish present capacity. The fixed five-field schema stays constant even when every returned amount changes.

Inventory is route-specific rather than a single protocol-wide balance. A relayer holding ample USDC on Base, chain ID 8453, still can’t fill USDC on Arbitrum, chain ID 42161, from that Base balance alone. Repayment and rebalancing eventually restore usable capital, but the live quote decides whether the requested amount fits now.

Fill Deadlines Turn Unfilled Intents Into Refundable Deposits

By contrast, Across deadlines are order controls that define who may fill, when filling ends, and when an untouched deposit becomes refundable.

The V3FundsDeposited event carries depositId, quoteTimestamp, fillDeadline, and exclusivityDeadline as four 32-bit fields. The exclusive relayer has sole fill rights until the exclusivity deadline; afterward, another relayer may fill before the final deadline. Each intent accepts one fill, which prevents two relayers from delivering the same output. If the fill deadline passes with no fill, the deposit becomes eligible for a refund through settlement, and its status moves from pending to expired and then refunded after processing. The refund address may differ from the destination recipient, so the quote’s recovery fields deserve the same attention as its output.

Fee Components Price Gas, Capital, and Pool Utilization

Across most deployments, Across bridge fees price three resources: destination gas, relayer capital, and liquidity-provider utilization across the selected route.

On a same-token transfer, the bridge fee equals input amount minus output amount. The quote then separates the LP charge, relayer capital charge, and destination gas charge; an integrator fee is optional and distinct. Across percentage fields use 10^18 as 100%, so 10^16 represents 1%. Token precision matters before any comparison: USDC uses 6 decimals, while WETH uses 18, making 1,000 USDC equal to 1,000,000,000 base units.

Worked example - all changing inputs are hypothetical: an Arbitrum-to-Base quote takes 1,000 USDC, lists a 1.25-USDC LP charge, lists 2.25 USDC for relayer capital and destination gas, and returns 996.50 USDC. The total fee is 3.50 USDC because 1,000 minus 996.50 equals 3.50. Dividing 3.50 by 1,000 produces a 0.35% effective bridge cost, while the recipient’s concrete output remains 996.50 USDC.

That calculation should use output amount, not a displayed percentage alone. A small transfer gives destination gas a larger percentage weight; a large transfer presses harder on the instant limit and liquidity curve. This Across comparison is resolved by the amount received within the required time; in the worked route, that decision number is 996.50 USDC.

V4 Settlement Recycles Capital After the Recipient Gets Paid

Absent anything unusual, Across settlement is a post-fill verification and repayment system, so the recipient’s transfer and the relayer’s reimbursement run on separate clocks.

The lifecycle has three phases: initiation in an origin SpokePool, fill in a destination SpokePool, and settlement of verified repayment. UMA evaluates repayment bundles on Ethereum before they become executable. Across V4 then stores finalized bundle data in HubPoolStore and uses Succinct SP1 proofs to carry verified Ethereum state to a UniversalSpokePool. These steps don’t reverse the completed user fill; they determine how quickly relayer capital returns to productive inventory.

Where that applies, Across V4 proof generation begins after Ethereum finality, described as 12-15 minutes, and its proof inputs include a 512-validator sync-committee signature. The proof service tracks four states, while destination execution uses two transactions: one updates SP1Helios, and another executes the stored message. Bundled validation keeps settlement work O(1) with respect to fill count rather than growing as O(N).

Slower reimbursement raises the relayer’s capital lock-up and narrows the inventory available for new orders. Faster recycling expands capacity without changing the recipient’s prior fill. That cause-and-effect link explains why Across quotes include a capital fee and why the quote’s instant maximum matters.

Route Choice Favors Speed, Native Issuance, or Pooled Capacity

Route selection is a choice among inventory-backed speed, issuer-controlled minting, pooled transport, and canonical rollup settlement.

On the operational side, Across fits transfers where a fresh quote covers the full amount inside the instant band and the stated output satisfies the recipient. Circle CCTP V2 offers a different USDC path: it burns on the source chain and mints native USDC on the destination. Fast Transfer uses finality threshold 1000 and consumes a global allowance; Standard Transfer uses threshold 2000 and doesn’t consume that fast allowance. Its capacity constraint belongs to Circle’s allowance, not an individual Across relayer’s wallet.

Stargate V2 uses LayerZero V2 messaging and same-asset routes. Its Taxi mode sends immediately, while Bus mode batches between 2 and 10 passengers before dispatch unless someone fills the remaining seats. The Arbitrum Bridge and Optimism Standard Bridge instead follow their rollups’ canonical settlement paths. Those alternatives answer different priorities: pooled transport, native USDC issuance, or direct rollup accounting (set out Across for beginners ).

Contract identity finishes the decision. Ethereum is chain ID 1, Optimism is 10, Base is 8453, and Arbitrum is 42161; the token contract must belong to that selected chain. ERC-7683 standardizes cross-chain intent orders, and AcrossOriginSettler implements its open flow for supported Across routes. Once chain, token, amount, deadline, and recipient all match the quote, speed becomes a measurable purchase of destination liquidity.