Question 1

What is StableSwap?

Accepted Answer

StableSwap is a cross-chain protocol for swapping stablecoins between Sui and Aptos. You deposit USDC or another stablecoin on one chain and receive your chosen stablecoin on the other. Settlement uses Circle's Cross-Chain Transfer Protocol (CCTP V2), with swap instructions delivered via LayerZero.

Question 2

How does StableSwap differ from other bridges?

Accepted Answer

Unlike oracle-based bridges that rely on external validator networks to attest cross-chain messages, StableSwap settles through Circle's CCTP V2. Circle is the canonical issuer of USDC, so the trust assumption is one you already accept by holding USDC. Order fulfillment is permissionless: any relayer can complete your swap, not just a single operator.

Question 3

What tokens and chains are supported?

Accepted Answer

Currently supported: Sui and Aptos, bidirectional. Tokens: USDC and USDT on both chains. On Sui, Cetus handles pre-swaps if needed. On Aptos, Hyperion executes the output swap. You can swap USDC to USDT or vice versa in either direction across the two chains.

Question 4

Why does StableSwap use CCTP V2 instead of a traditional bridge?

Accepted Answer

CCTP V2 burns USDC on the source chain and mints native USDC on the destination. There's no wrapped token, no liquidity pool, no external oracle. The only trust assumption is Circle, which you already trust if you hold USDC. This sidesteps the attack surface that has cost other bridges hundreds of millions in exploits.

Question 5

What happens when I initiate a swap?

Accepted Answer

Your transaction on Sui does three things atomically: (1) Optional pre-swap if depositing non-USDC, Cetus converts to USDC. (2) CCTP V2 burn where your USDC is burned with mint recipient set to the Aptos settlement contract. (3) LayerZero send with swap instructions including output token, minimum amount, and your Aptos address. All three are bundled in a single Sui PTB. If any step fails, the entire transaction reverts.

Question 6

How long does a swap take?

Accepted Answer

Typical end-to-end: 30-50 seconds. Breakdown: Sui finality takes about 3 seconds, LayerZero message delivery 5-10 seconds, Circle attestation 15-30 seconds, and solver fulfillment 5-10 seconds after attestation. The attestation step is the bottleneck. Circle's service runs continuously, but attestation times vary with network conditions.

Question 7

What is a solver?

Accepted Answer

A solver is a permissionless relayer that watches for swap orders and fulfills them on the destination chain. Solvers monitor Sui for new orders, poll Circle's attestation API, and submit the fulfillment transaction on Aptos. Anyone can run a solver with no registration or bonding requirement. The first solver to submit a valid fulfillment wins. Competition among solvers improves reliability and reduces MEV.

Question 8

What happens on the destination chain?

Accepted Answer

Once the solver has the CCTP V2 attestation, it calls fulfill_order() on Aptos. This function claims the CCTP V2 USDC minted to the settlement contract, swaps via Hyperion to your requested output token, validates the output amount meets your min_output, transfers to your Aptos address, and marks the order fulfilled. All steps execute in a single atomic transaction.

Question 9

How is the exchange rate determined?

Accepted Answer

StableSwap uses market rate at fulfillment time. When the solver executes your swap on Hyperion, you receive the pool's current rate. Your protection is min_output: the minimum amount you specified when initiating the swap. If the rate moves against you beyond this floor, the fulfillment transaction reverts and your order stays pending.

Question 10

What if the solver goes offline?

Accepted Answer

Your funds are not at risk. CCTP V2 mints USDC to the settlement contract, not to the solver. If one solver goes offline, any other solver can fulfill your order. If all solvers are offline, your order stays pending until one comes back or you use the fallback mechanism.

Question 11

What is withdraw_fallback?

Accepted Answer

A safety mechanism for orders that remain unfulfilled after 24 hours. You call withdraw_fallback() on Aptos with the CCTP V2 message and attestation. The contract claims the USDC and sends it directly to you. You receive raw USDC without the swap to your requested output token, but your funds are recovered. You pay Aptos gas for the withdrawal transaction.

Question 12

Can I cancel my swap?

Accepted Answer

Yes, but only before Circle's attestation completes, roughly 15-30 seconds. To cancel, call cancel_order() on Sui with the CCTP V2 message. This uses CCTP V2's replace_deposit_for_burn() to redirect the mint to your own address instead of the settlement contract. The LayerZero messaging fee of about 0.28 SUI is lost. After attestation, cancellation is not possible; you must wait for fulfillment or use the 24-hour fallback.

Question 13

What if the DEX swap fails?

Accepted Answer

If Hyperion can't execute the swap due to no liquidity or price limit exceeded, the fulfill_order transaction doesn't revert entirely. The CCTP V2 claim succeeds with USDC minted to the settlement contract, but the swap portion fails. Your USDC stays in the settlement contract, and withdraw_fallback becomes available after 24 hours. You won't receive your requested output token, but you can recover the USDC.

Question 14

What are the trust assumptions?

Accepted Answer

Four components: (1) Circle CCTP V2 - you already trust Circle if you hold USDC, as CCTP V2 uses Circle's attestation service. (2) LayerZero DVNs for message authentication of swap instructions, currently one DVN from LayerZero Labs. (3) Hyperion AMM as the swap execution venue on Aptos, where your min_output protects against adverse price moves. (4) Solvers require zero trust as they never custody your funds since CCTP V2 mints to the settlement contract.

Question 15

What fees do I pay?

Accepted Answer

Source chain gas for the Sui transaction, LayerZero fee of about 0.28 SUI for cross-chain messaging, zero CCTP V2 fee since it's 1:1 burn-mint, Hyperion swap fee around 0.01%, and zero StableSwap protocol fee currently. Total cost is source gas plus 0.28 SUI plus the small swap fee.

Question 16

Who pays destination chain gas?

Accepted Answer

The solver pays Aptos gas for the fulfill_order transaction. Solver economics are currently reputation-based with no direct payment. If you use withdraw_fallback, you pay the Aptos gas yourself.

Question 17

How does the two-layer messaging work?

Accepted Answer

CCTP v1 on Sui and Aptos has a fixed message format with no way to attach execution instructions. StableSwap uses two layers: CCTP V2 carries the funds by burning USDC on Sui and minting on Aptos, while LayerZero carries the swap parameters including output token, min_output, and recipient. Both messages originate from the same Sui PTB ensuring atomicity. The settlement contract on Aptos matches them via cctp_nonce.

Question 18

What contracts are involved?

Accepted Answer

On Sui: OrderEscrow V2 initiates swaps, burns USDC via CCTP V2, and sends the LayerZero message. On Aptos: OrderSettlement V2 receives the LayerZero message and fulfills orders via CCTP V2 claim plus Hyperion swap. Hyperion pool executes the USDC to output token swap. All contracts are non-upgradable after deployment.

Question 19

How do I verify my swap on-chain?

Accepted Answer

Check Sui for the SwapOrderCreated event with your transaction hash. Poll Circle's API at iris-api.circle.com for attestation status using source domain ID 8 for Sui and your transaction hash. Check Aptos for the OrderFulfilled event once the solver completes. Use suiexplorer.com for Sui and explorer.aptoslabs.com for Aptos.

Question 20

Can I run my own solver?

Accepted Answer

Yes, solver operation is permissionless. Requirements: monitor Sui escrow contract for SwapOrderCreated events, poll Circle's attestation API at iris-api.circle.com, and submit fulfill_order() transactions on Aptos when attestations are ready. No registration or bonding is required. The solver service codebase is in the stableswap-protocol repository.

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Supported Chains