Yield Boost - ETH fund flow

caution

Yield Boost is not yet live. This documentation describes the intended design.

Overview

Linea Yield Boost is a protocol-level mechanism that automatically stakes some of the ETH held in the Linea bridge, or LineaRollup, and distributes those staking rewards back to the L2 ecosystem. This page maps the high-level architecture, including where ETH flows and which roles control each movement.

High-level architecture

LineaRollup deposits on Ethereum L1 are staked via Lido V3 stVaults to generate beacon chain rewards, which are reported to L2 for distribution.

Key entities:

• YieldManager - Core L1 contract that routes ETH between LineaRollup and external staking strategies, and calculates reportable yield after deducting obligations.
• Dashboard - Lido V3 utility contract that wraps the StakingVault with operator fee handling and convenience functions for deposits and LST minting.
• StakingVault - Lido V3 vault that holds ETH for beacon chain staking. The vault owner controls deposits and withdrawals; withdrawal credentials point to the vault.
• Node Operator - Runs beacon chain validators on behalf of Linea. Has sole authority over when and how much ETH to deposit from the StakingVault into validators.
• Automation Service - Off-chain service that executes routine yield operations: reporting, reserve rebalancing, and obligation settlement.
• L2MessageService - L2 contract that receives yield messages from L1 and releases corresponding L2 ETH into circulation.
• L2YieldDistributor - Distributes newly circulated L2 ETH (backed by L1 staking rewards) to eligible recipients.

L1 ETH flow

Yield reporting and L2 distribution

Legend

• Solid line - actual fund movement (ETH/stETH transfer)
• Dashed line - function call or event (no funds move)
• Red - privileged operator
• Blue - permissionless
• Green - L2

Roles and fund movement permissions

Role	Held By	ETH Movement Authorized
YIELD_PROVIDER_STAKING_ROLE	Automation Service	LineaRollup → YieldManager → StakingVault
YIELD_PROVIDER_UNSTAKER_ROLE	Automation Service	Validators → StakingVault → YieldManager → LineaRollup
YIELD_REPORTER_ROLE	Automation Service	Settles obligations from StakingVault (LST liabilities, protocol fees, operator fees); emits synthetic yield message to L2
STAKING_PAUSE_CONTROLLER_ROLE	Security Council	None (pauses/unpauses beacon deposits)
OSSIFICATION_INITIATOR_ROLE	Security Council	Initiates full withdrawal of all staked funds
OSSIFICATION_PROCESSOR_ROLE	Automation Service	Progressive withdrawal during ossification
SET_YIELD_MANAGER_ROLE	Security Council	None (configuration)
Permissionless	Anyone	fund() donations; unstakePermissionless() + replenishWithdrawalReserve() during deficit

Fund flow scenarios

Each scenario below traces a specific ETH movement end-to-end, showing the contracts involved and the role that triggers it.

1. Staking - routine: surplus ETH is moved from LineaRollup into validators.
2. Reserve replenishment - routine: the Automation Service pulls funds back from validators when the withdrawal reserve runs low.
3. Yield reporting - routine: earned rewards are calculated, obligations settled, and net yield relayed to L2.
4. Permissionless flows - fallback: anyone can trigger unstaking and replenishment when the reserve drops below minimum.
5. LST withdrawal - last resort: stETH is minted for users when LineaRollup has insufficient ETH.
6. Ossification withdrawal - terminal: all staked funds are progressively withdrawn after the Security Council ossifies the vault.

1. Staking

Surplus ETH in LineaRollup (above minimum reserve) is routed to the StakingVault for beacon chain staking.

2. Reserve replenishment

Two-phase process: first trigger beacon chain withdrawal, then route funds to LineaRollup once they arrive in the vault.

3. Yield reporting

The Automation Service triggers yield reporting. Before the net surplus is relayed to L2, the YieldManager settles outstanding obligations.

No L1 ETH moves for the yield report itself - obligation payments (solid arrows) are the only L1 ETH transfers. The MessageSent event is synthetic: it relays the net surplus to L2 for distribution without bridging ETH.

4. Permissionless flows

When LineaRollup balance drops below the minimum reserve, anyone can trigger unstaking and reserve replenishment.

unstakePermissionless() is capped to the remaining deficit minus available liquidity in the YieldManager and provider. replenishWithdrawalReserve() is similarly capped to the current deficit.

5. LST withdrawal - last resort

If LineaRollup lacks ETH for a user withdrawal, stETH is minted against StakingVault collateral and sent directly to the user as a last resort.

This creates an LST liability that accrues interest; the system prioritizes repaying it from subsequent fund flows and yield.

6. Ossification withdrawal

Ossification permanently locks the StakingVault implementation, opting out of future upgrades. The Security Council initiates it; the Automation Service then progressively withdraws all staked funds back to LineaRollup.

Quick reference

Fund Movement	Source	Destination	Trigger	Role Required
Stake excess reserve	LineaRollup	StakingVault	Automation	YIELD_PROVIDER_STAKING_ROLE
Beacon chain deposit	StakingVault	Validators	Node Operator decision	Node Operator
Report yield to L2	synthetic MessageSent event	L2YieldDistributor	Automation	YIELD_REPORTER_ROLE
Operator replenish reserve	StakingVault	LineaRollup	Reserve below target	YIELD_PROVIDER_UNSTAKER_ROLE
Permissionless unstake	Validators	StakingVault	Reserve below minimum	Permissionless
Permissionless replenish reserve	StakingVault	LineaRollup	Reserve below minimum	Permissionless
LST withdrawal	Lido Protocol (minted against StakingVault collateral)	User	Insufficient ETH	Permissionless (user)
Ossification withdrawal	StakingVault	LineaRollup	Security Council initiates	OSSIFICATION_INITIATOR_ROLE + OSSIFICATION_PROCESSOR_ROLE
Donation	External	LineaRollup / StakingVault	Voluntary	Permissionless