Crypto Gloss

Frax Ether

Frax Ether is the Frax Protocol’s liquid staking system — enabling users to deposit ETH and receive frxETH (a liquid pegged representation of staked ETH) or sfrxETH (a yield-bearing vault token that accrues all ETH staking rewards from Frax’s validator set), designed to maximize staking yield by concentrating all ETH staking rewards into sfrxETH holders while frxETH itself pays zero yield, making sfrxETH the highest-yielding major ETH liquid staking token by design.

Overview

Frax Ether launched in October 2022, introducing a novel architecture that separates pegged liquidity (frxETH) from yield accrual (sfrxETH). The key insight: in most liquid staking tokens (stETH, rETH, cbETH), all holders receive staking yield — whether they need it or not. Frax Ether lets users choose: hold frxETH as liquidity-focused collateral (zero staking yield but better AMM properties), or stake frxETH → sfrxETH (collect all staking rewards as vault appreciation).

By concentrating staking rewards only to sfrxETH holders, sfrxETH achieves a yield multiplier: if 50% of frxETH is staked as sfrxETH, sfrxETH holders earn 2× the base staking rate on their staked portion.

Two-Token Architecture

Token design and economics are covered in detail below.

frxETH

frxETH is a 1:1 ETH-pegged receipt token:

  • Mint: deposit ETH → receive frxETH (always 1:1)
  • Not rebasing: frxETH supply grows as more ETH is minted, balance doesn’t increase
  • Zero yield: frxETH itself pays NO staking yield (this is deliberate)
  • Use case: DeFi collateral, stablecoin-equivalent LP, composability without yield complexity
  • AMM integration: frxETH/ETH Curve pool — users can swap ETH→frxETH and back; frxETH has tighter peg than stETH because frxETH earns no yield (no daily rebasing complexity)
  • Minting: always at 1.000 ETH per frxETH (no peg mechanism needed — direct mint)

sfrxETH

sfrxETH is the yield-bearing staked version of frxETH:

  • Mint: deposit frxETH → receive sfrxETH
  • Mechanism: ERC-4626 vault — as ETH staking rewards accrue, sfrxETH exchange rate vs frxETH increases
  • All staking rewards from Frax’s entire validator set go into the sfrxETH vault
  • Yield = (total ETH staking rewards) / (total frxETH staked in sfrxETH)
  • Since only sfrxETH holders receive rewards, and not all frxETH is staked: yield multiplier applies
  • Example: 100 ETH minted as frxETH; 60 ETH staked as sfrxETH; ETH staking = 4% APY = 4 ETH rewards/year; sfrxETH APY = 4 ETH / 60 ETH sfrxETH staked = 6.7% APY (vs 4% if all holders shared rewards)

Yield Multiplier Calculation

“`

sfrxETH APY = (Validator ETH Yield) × (Total frxETH) / (frxETH staked as sfrxETH)

If 70% of frxETH staked: sfrxETH APY = 4% × (1/0.70) = 5.71%

If 50% of frxETH staked: sfrxETH APY = 4% × (1/0.50) = 8.0%

“`

The multiplier increases as more frxETH remains unstaked (in DeFi as liquidity rather than staked).

Frax Validator Operations

Frax Protocol operates its own Ethereum validators:

  • ETH deposited via frxETH → Frax activates validators (32 ETH per validator)
  • Frax validators: run by Frax-selected node operators, subject to governance
  • Frax-specific validator client diversity maintained for safety
  • All validator rewards → sfrxETH vault
  • MEV rewards (from block building): also pooled into sfrxETH yield (increases total yield vs simple consensus rewards)
  • EigenLayer restaking: Frax explored restaking Frax validators on EigenLayer for additional restaking yield → would further increase sfrxETH APY

DeFi Integration

The integration works as follows.

Curve frxETH/ETH Pool

The primary liquidity venue for frxETH:

  • Uses the fact that frxETH doesn’t rebase → easier for Curve’s StableSwap pricing model
  • Frax Protocol directs CRV/CVX/FXS bribes to this pool → deep liquidity maintained
  • frxETH peg: maintained very close to 1 ETH via arbitrage + Curve depth
  • LPs in frxETH/ETH: earn Curve trading fees + CRV/CVX/FXS rewards (no staking yield on frxETH side)

sfrxETH as Collateral

sfrxETH accepted in multiple lending protocols:

  • Aave V3: sfrxETH as collateral → borrow USDC against sfrxETH exposure
  • Frax’s own Fraxlend: sfrxETH as collateral for FRAX borrowing
  • Morpho: sfrxETH supported
  • Pendle: sfrxETH/PT + YT on Pendle for fixed-rate ETH staking yield

Sources

  1. Frax Ether Documentation — Frax Finance Team, 2022–2024. Technical documentation covering frxETH minting (SubmitAndDeposit function: user deposits ETH, receives frxETH 1:1; ETH aggregated to 32 ETH batches → Frax activates validator via deposit contract; no queue time for frxETH (immediate mint); redemption: burn frxETH → ETH via Curve pool or Frax redemption queue (7-14 day queue when validators must exit to cover); sfrxETH ERC-4626 design (standard yield vault: totalAssets() = total frxETH in vault + accumulated staking rewards in frxETH equivalents; convertToShares(assets): given frxETH amount → sfrxETH shares at current exchange rate; convertToAssets(shares): given sfrxETH shares → frxETH at current rate; rate increases daily as rewards distributed; RewardReceiver contract: receives validator rewards (ETH) → converts to frxETH → deposits into sfrxETH vault → rate increases for all sfrxETH holders; MEV rewards: majority captured via mev-boost relay set; MEV-boost rewards distributed same way), and validator management (Frax operated 2000+ validators by 2024; operator set: permissioned team of professional validator operators; client diversity: mix of Lighthouse/Lodestar/Prysm consensus clients; planned DVT (distributed validator technology) adoption for decentralization; exit mechanism: validators can be exited to cover frxETH redemptions; exit queue: max 8 validators per epoch = ~1800 ETH/$6M per day withdrawal capacity).
  1. “sfrxETH vs stETH vs rETH: Yield Comparison and Use Case Analysis” — Liquid Staking Research, 2022–2024. Comparative analysis of the major ETH liquid staking tokens — Lido stETH (rebasing, universal yield), Rocket Pool rETH (non-rebasing, decentralized), frxETH/sfrxETH (concentrated yield, dual token), cbETH (Coinbase) — examining yield delivery, DeFi composability, centralization risk, and appropriate use cases for each.
  1. “Frax Validator Economics: MEV-Boost, EigenLayer, and Maximizing sfrxETH Yield” — ETH Staking Research, 2023. Analysis of how Frax maximizes validator yield for sfrxETH holders — MEV-boost relay selection, block building economics, the potential for EigenLayer restaking to further augment sfrxETH APY above pure staking consensus+MEV yield.
  1. “frxETH in Curve: Maintaining Peg and Generating Protocol Revenue” — DeFi Liquidity Research, 2022–2023. Analysis of the frxETH/ETH Curve pool — Frax Protocol’s use of CRV/CVX bribe campaigns to maintain deep frxETH/ETH liquidity, the resulting peg stability compared to stETH (which requires Lido’s stETH/ETH Curve pool), and the revenue generated by the Curve pool for Frax AMO.
  1. “sfrxETH on Pendle: Fixed-Rate ETH Staking and YT-sfrxETH Yield Trading” — Pendle/LST Research, 2023. Analysis of how sfrxETH integrates with Pendle Finance’s yield tokenization — sfrxETH PT (fixed-rate sfrxETH yield to maturity), YT-sfrxETH (leveraged ETH staking yield) — and how the two protocols amplify each other (Pendle YT-sfrxETH gives leveraged exposure to sfrxETH’s concentrated yield multiplier).

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