Frax USD
Frax Finance
Market cap: $125M
Overview
Fully collateralized stablecoin launched December 2025 as the successor to the original FRAX stablecoin. Backed 1:1 by BlackRock's BUIDL fund (USD Institutional Digital Liquidity Fund, tokenized by Securitize) — investing in US Treasury bills, cash, and repo agreements. The original FRAX fractional-algorithmic model was retired. Note: the FRAX ticker now refers to the Frax Finance governance and gas token for the Fraxtal L2 network (formerly FXS).
Features
Engineering-oriented breakdown of capabilities: standards, who they matter for, integration rationale, per-feature risks, and vetted external references (specs, docs, verified source).
| Feature | Standards | Audience | Why it matters | Risk / caveat | References |
|---|---|---|---|---|---|
BlackRock BUIDL backing compliance | — | Both | frxUSD is 100% backed by BlackRock's BUIDL fund (tokenized by Securitize) — no algorithmic or fractional-reserve mechanics. Reserve quality is determined by BUIDL's US Treasury portfolio. | Reserve quality tied to BUIDL fund and Securitize tokenization infrastructure; no traditional bank-style fiat backing. | |
sfrxUSD ERC-4626 vault yield | User | Yield-bearing frxUSD position earning BUIDL fund T-bill income — integrate as standard ERC-4626 vault. | Verify new sfrxUSD vault address from official Frax docs — old sFRAX contracts are not the same. Yield rate reflects T-bill income, not AMO revenues. | ||
Fraxlend isolated pairs yield | — | User | Isolated lending markets — each pair has unique oracle and liquidation params. | Liquidation and interest rate spikes per pair; not a single global lending risk model. | |
Fraxswap TWAMM stability | — | User | Native AMM with TWAMM order type — relevant for routing and MEV-aware trading integrations. | AMM smart contract risk separate from frxUSD token contract. |
EIP / ERC support matrix
Standards support for frxUSD. Click an EIP to jump to the global deep-dive section.
| Standard | Status | Notes |
|---|---|---|
| ERC-20 Fungible token standard | Implemented | Treat as a standard fiat-backed ERC-20 — no fractional-reserve or AMO complexity. Verify new contract addresses post-December 2025 migration before integrating. |
| EIP-712 Typed structured data signing | Unknown | Verify before building gasless or signature-based flows. |
| EIP-2612 Permit — gasless ERC-20 approval | Unknown | Gasless approval flows should be tested against the live contract — fall back to Permit2 if not supported. |
| EIP-3009 transferWithAuthorization | Not implemented | Use standard approve/transferFrom or Permit2 for payment flows. |
| EIP-1967 Standard proxy storage slots | Implemented | Confirm proxy type and admin from on-chain storage before building long-lived integrations. |
| EIP-1822 UUPS — universal upgradeable proxy | Not implemented | Low for typical frxUSD holders. |
| ERC-4626 Tokenized yield vault standard | Implemented | Composable with ERC-4626 routers and aggregators. Yield rate reflects BUIDL fund's T-bill income rather than AMO revenues. |
| EIP-1271 Signature validation for smart contracts | Not implemented | Smart wallets follow standard ERC-20 approval paths. |
| ERC-7802 Crosschain token interface | Not implemented | Cross-chain movement through Fraxtal bridge or future integrations. |
| ERC-3156 Flash loans | Not implemented | Use external flash loan providers. |
Technical notes
18 decimals. frxUSD can be minted 1:1 by depositing BlackRock BUIDL directly into mint contract (0xe827abf9f462ac4f147753d86bc5f91e186e4e9c) — first direct DeFi↔BlackRock tokenized asset integration. sfrxUSD (StakedFrxUSD) extends LinearRewardsErc4626: non-rebasing, share price increases. Benchmark Yield Strategy (BYS) dynamically allocates across carry-trade (Ethena/Superstate), DeFi AMOs (Aave/Curve/Convex/Euler/Fraxlend), and IORB/T-Bill RWA strategies. Redemption via FraxtalERC4626MintRedeemer: zero fees, zero price impact. Original FRAX fractional-algorithmic model retired.
Reserves & peg
- Reserves
- BlackRock BUIDL fund (US Treasuries, cash, repo agreements) via Securitize tokenization
- Collateral
- RWA — tokenized US Treasuries
- Peg mechanism
- Hard 1:1 via BUIDL fund redemption
- Auditor
- BlackRock/Securitize transparency reporting on BUIDL fund
Ecosystem
- DeFi integration
- Fraxswap, Fraxlend (native); early-stage external DeFi integrations
- Yield
- sfrxUSD variable — BUIDL fund US Treasury yield
Risk factors
Networks & contracts
Deployments by chain — primary rows are highlighted. Always verify addresses against issuer docs before mainnet integrations.
Engineering deep dive
Integration notes
frxUSD launched in December 2025 as the successor to the original FRAX stablecoin. Unlike the old fractional-algorithmic model, frxUSD is fully collateralized by BlackRock's BUIDL fund (tokenized US Treasuries via Securitize) — treat it as a standard fiat-backed ERC-20.
Important: The FRAX ticker now refers to the Frax Finance governance and gas token (formerly FXS) for the Fraxtal L2 — it is no longer the stablecoin. Always verify the canonical frxUSD contract address from official Frax Finance docs before integrating.
Native stack
Fraxswap / Fraxlend are purpose-built around the Frax ecosystem — use their docs for composable integrations with frxUSD.