siBTC
Executive Summary
siBTC is the liquid restaking receipt minted when iBTC is deposited into a Mellow Vault for Symbiotic Staking. Holders keep complete BTC price exposure, but can immediately transfer their ERC-4626 shares while earning three reward streams—iBTC (5x), Symbiotic, and Mellow points—through the same position
Component Overview
Component
Purpose
siBTC (ERC-4626)
Liquid restaking token accruing yield; minted & burned by the vault
Symbiotic Layer
Shared-security protocol where vault collateral is delegated to network operators with configurable slashing
Mellow Symbiotic Vault
Permissionless wrapper that batches iBTC→Symbiotic deposits, tracks TVL and share price, and routes withdrawals via an async queue
System Architecture
Deposit iBTC: The user sends iBTC to the vault on Mellow. The vault immediately mints siBTC 1-for-1 and credits it to the depositor’s wallet.
Delegate Stakes: The vault’s Curator batches the newly received iBTC and delegates that collateral to approved Attestor Network operators inside Symbiotic. Delegation is tracked off-chain for gas efficiency and on-chain via the vault’s totalDelegated() view.
Earn Rewards: While the iBTC is staked, it accrues three parallel reward streams—
iBTC points (5×)
Symbiotic AVS points (1×)
Mellow vault points (1×)
At curator-defined intervals, these rewards are committed to a Merkle-farm contract; siBTC holders claim them with a lightweight proof.
How the Components Interact
Front-end ↔ Vault – The UI talks only to the vault contract; every deposit or withdrawal emits an event the curator bot watches
Vault ↔ Symbiotic – A single delegate() call per batch forwards iBTC to Symbiotic’s collateral module, which in turn assigns voting power and slash-protection to the chosen Attestors
Vault ↔ WithdrawalQueue – Exit requests are parked in an async queue; after two Symbiotic epochs the curator finalises and frees the iBTC for redemption
Vault ↔ Merkle Farm – On pushRewards(), the vault transfers freshly earned tokens to the Merkle farm and posts the new root hash. Claim transactions cost low gas because balances are proven, not stored.
Security Boundary Highlights
Custody – The vault is the only holder of depositor funds; Symbiotic never touches user keys.
Slash Containment – If an Attestor is penalised, only the delegated slice of collateral is affected; withdrawal buffers ensure no under-collateralised redemptions.
Upgrade Path – All vault upgrades and parameter changes (e.g., new Attestors) are gated by a Timelock-controlled Curator multisig, giving depositors at least 48 h to exit before changes take effect.
Token Mechanics & Incentives
Point Accrual – siBTC balances earn hourly Mellow points plus Symbiotic partner points, both computed on totalAssets() in the vault.
Early-bird Multiplier – pre-deposit commitments receive a points multiplier defined in the vault parameters.
Triple Yield Stack – combined rewards from iBTC, Symbiotic, and Mellow amplify net APY without additional gas actions.
User Workflows
Deposit → Mint siBTC
Connect wallet on Mellow Dapp and select the iBTC Vault.
Enter deposit amount and approve iBTC spend.
Sign the deposit() transaction; siBTC is minted instantly.
Withdraw siBTC → BTC (two-phase)
In the vault UI, request withdrawal of siBTC.
Vault queues the request; curator batches it within 1-7 days.
After two Symbiotic epochs, call claim() to receive iBTC, then unwrap if desired.
Claim Rewards
Curator triggers pushRewards; funds flow to a Merkle farm and become claimable per-address.
Security & Risk Model
Vector
Mitigation
Operator mis-behaviour
Symbiotic slashing with resolver veto window.
Vault insolvency
Assets remain locked; only accounting delegations move stake.
Collateral reuse risk
Collateral module separates burnable “Burner” hooks for slash-able LRTs.
Liquidity delays
WithdrawalQueue enforces two-epoch buffer to prevent bank-run drains.
Governance & Permissions
A Curator multisig governs vault limits and can pause deposits or withdrawals via OpenZeppelin Timelock; all sensitive changes respect time-delay execution.
Contract Interface (ERC-4626 overrides)
Function
Description
asset()
Returns underlying (iBTC).
totalAssets()
Vault TVL in iBTC.
convertToShares(amount)
Assets → shares calc.
convertToAssets(shares)
Shares → assets calc.
previewDeposit/Withdraw/Mint/Redeem
Simulate outcomes client-side.
claimableAssetsOf / pendingAssetsOf
Read withdrawal queue status.
Glossary
Term
Definition
AVS
Actively Validated Service secured by Symbiotic restaked collateral.
Curator
Entity that manages a Symbiotic vault and delegates stake.
Resolver
Address or contract with veto power over slashing events.
WithdrawalQueue
Async buffer contract that finalises vault exits after two epochs.
Epoch
Fixed Symbiotic time interval used for reward distribution and slashing windows.
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