The USDC bridge

Soma uses USDC as the settlement token. USDC doesn’t natively live on Soma — it’s bridged from Base. The bridge is a quorum-signed lockup-and-mint pattern, similar to Sui’s bridge.

Deposit (Base → Soma)

On Base Sepolia:

1. The user (or a paymaster, sponsoring the gas) calls SomaBridge.deposit(destinationChainID=2, somaRecipient, amount) on the bridge proxy 0x5458a14d8a28CAff779f029FA3d60B8F9523C85b.
2. The contract pulls amount USDC from the caller via transferFrom and locks it in the BridgeVault.
3. The contract emits TokensDeposited(nonce, sender, destChainId, somaRecipient, tokenType, amount, timestampMs).

On Soma:

1. Each validator’s bridge node watches Base Sepolia for TokensDeposited events.
2. When seen, the node signs the event with its dedicated secp256k1 bridge key.
3. Nodes exchange signatures via a peer-broadcast HTTP server. Once a quorum (>50% of voting stake) has signed, any node can submit the aggregated cert on chain.
4. The Soma-side bridge executor verifies the cert, mints amount USDC to somaRecipient, and records the nonce as processed so it can’t be replayed.

End-to-end latency is roughly 30-60 seconds, dominated by Base finalization and validator gossip.

Withdraw (Soma → Base)

On Soma:

soma bridge withdraw --amount 1.0 \
    --recipient 0x7B42d2B6F94fDF3c2Fe62e0aAf451487FA2DAB6e \
    --target-chain base-sepolia

This burns the requested USDC from your Soma balance and creates a PendingWithdrawal shared object on chain.

The bridge nodes then:

1. Sign the withdrawal with their bridge keys.
2. Once quorum is reached, attach the cert to the PendingWithdrawal.
3. The outbound relayer (one of the validator-operators’ wallets) submits an Eth-side tx to SomaBridge.executeWithdrawal(...), which releases USDC from the BridgeVault to the recipient.

Same ~30-60 second end-to-end latency.

Why a bridge rather than native USDC

Stablecoin liquidity already lives where the people are: Ethereum L1 and the L2s. Native USDC on Soma would require Circle to issue against a Soma reserve account, which they only do for chains with significant existing adoption. Bridging from Base is the pragmatic answer for testnet and likely for a long time after — you keep the same dollar, redeemable back to its original chain, without forcing Circle to integrate with every new L1.

The committee

The set of validators authorized to sign bridge events is the bridge committee. It’s rebuilt at each epoch boundary from active Soma validators who have registered a bridge pubkey via soma validator register-bridge-key. Validators that don’t register simply don’t get bridge signing power; they still earn from consensus.

The bridge committee’s voting weights are proportional to validator stake, with a 50.01% quorum threshold (matching the standard BFT 2f+1 model). Misbehavior (signing fraudulent events) would be slashable, but the bridge itself doesn’t include slashing logic yet — validator-level reporting handles bad actors today.