BNB Smart Chain Migration Guide
Enable BNB Smart Chain (Chain ID 56) bridging for USDC, USDT, and ETH.
Across supports bridging USDC, USDT, and ETH to and from BNB Smart Chain (Chain ID 56). This guide covers the API changes required for developers, integrators, and relayers.
BNB Smart Chain is the first chain using Across V4's ZK settlement. No testnet is available — test on mainnet with small amounts.
API Changes
New outputAmount Field
The /suggested-fees endpoint now returns a calculated outputAmount field directly. Stop calculating output amounts manually.
// Old approach (deprecated) — do NOT use
const outputAmount = inputAmount * (1n * 10n**18n - BigInt(fees.totalRelayFee.pct)) / 10n**18n;
// New approach (required) — use the API response directly
const outputAmount = fees.outputAmount;allowUnmatchedDecimals Parameter
A new optional query parameter allowUnmatchedDecimals has been added to /suggested-fees. When omitted, the API returns a 4XX error if input and output tokens have different decimal counts (e.g., USDC has 6 decimals on some chains, 18 on others).
Set allowUnmatchedDecimals=true if you're intentionally bridging between tokens with different decimals.
outputToken Requirements
For BSC routes, you must NOT set outputToken to 0x0. Integrators must explicitly specify the output token address for all BNB Smart Chain transfers.
Deprecation Timeline
| Date | Change |
|---|---|
| Now | outputToken=0x0 still works on non-BSC routes |
| June 19, 2025 | Protocol contracts will prevent outputToken=0x0 network-wide |
Action required: Update all integrations to explicitly specify outputToken addresses before the June deadline.
For Relayers and Indexers
- Recognize chain ID
56in your configurations - Reject any BSC deposits where
outputTokenis set to0x0 - Prepare for complete
outputToken=0x0removal by June 19, 2025
Key Details
| Property | Value |
|---|---|
| Chain ID | 56 |
| Supported tokens | USDC, USDT, ETH |
| Deposit function | depositV3() |
| Settlement | Across V4 (ZK proofs via Succinct SP1) |
| Testnet | Not available |
| App-SDK | Supported |