Stablecoins are designed to maintain a constant $1 value, yet history shows they can break the buck. USD Coin (USDC) has traded as low as $0.87, Tether’s USDT has touched $0.88, and Terra’s UST collapsed to near zero in a failure that erased roughly $40 billion. As recently as November 2025, a DeFi stablecoin called xUSD lost more than half its value in a single day. These episodes underscore a central reality: a peg is a promise, not a guarantee.
What Keeps a Stablecoin at $1
Stablecoins use different mechanisms to target $1:
- Fiat-reserved coins (e.g., USDC, USDT) hold cash and cash-equivalent assets and allow creations and redemptions at or near $1 to anchor the market price.
- Crypto-collateralized coins are backed by digital assets, typically overcollateralized, with on-chain liquidation mechanisms intended to protect the peg.
- Algorithmic designs attempt to maintain parity with incentives and endogenous collateral; these models are more vulnerable to reflexive sell-offs and liquidity shocks.
What Happens When a Stablecoin Depegs
- Secondary-market price diverges: On exchanges and DEXs, the stablecoin can trade below $1 as sellers rush for liquidity.
- Liquidity pools skew: Automated market makers fill with the depegged coin, increasing slippage for exits and amplifying pressure on the price.
- Arbitrage and redemptions: If redemptions at $1 remain open, arbitrageurs buy below par and redeem, helping narrow the discount while drawing down reserves.
- Collateral stress in DeFi: Borrowing and lending platforms using the coin as collateral can see liquidations or bad debt if oracle prices adjust quickly.
- Flight to perceived safety: Traders rotate into other stablecoins or fiat, widening spreads and straining market liquidity.
How Pegs Are Defended
- Redemption access and market making: Clear, continuous redemptions and active liquidity provision help restore parity by aligning secondary prices with $1 claims on reserves.
- Transparency on backing: Timely disclosures and attestations can reduce uncertainty and slow runs.
- Adjusting risk parameters: Collateralized models may raise fees, boost collateral ratios, or pause new minting to stabilize backing.
- Emergency measures: In severe stress, issuers and protocols may seek external capital, deploy backstops, or enact governance changes; algorithmic models are especially exposed if confidence erodes.
Why It Matters
Stablecoins underpin crypto trading, DeFi collateral markets, and on-chain payments. A lasting depeg can trigger liquidations, impair liquidity, and transmit stress across exchanges, lending platforms, and payment rails. For institutions and regulators, these events highlight the importance of reserve quality, redemption mechanics, disclosures, and robust risk controls. For market participants, they serve as a reminder to evaluate not just yields or convenience, but the specific mechanism that claims to hold $1.