How Stablecoins Work: USDC, DAI, and the Models Behind Them

Stablecoins are cryptocurrencies designed to maintain a stable value, typically pegged to the US dollar. They're critical DeFi infrastructure — most lending, trading, and savings products are denominated in stablecoins. The mechanisms that maintain the peg vary widely and carry very different risk profiles.

Fiat-Backed Stablecoins (USDC, USDT)

The simplest model: for every token issued, an equivalent dollar (or dollar equivalent) is held in reserve by a centralized entity. USDC is backed by cash and short-term US Treasuries held by Circle. USDT by Tether Limited. These are as stable as their issuer's integrity and the safety of their reserves.

Risk: counterparty risk (Circle or Tether could fail), regulatory risk (the issuer can blacklist addresses and freeze funds), and concentration risk (if USDC depegs, all DeFi that uses USDC as collateral is affected). The 2023 USDC depeg during Silicon Valley Bank's collapse demonstrated this is not theoretical.

Crypto-Collateralized Stablecoins (DAI)

DAI is created by locking crypto collateral (ETH, wBTC, real-world assets) in MakerDAO's smart contracts. Users mint DAI against their collateral at a required over-collateralization ratio (150%+ for ETH). If collateral value drops, the position is liquidated. The over-collateralization provides a buffer against price volatility.

DAI is decentralized and censorship-resistant (no address blacklisting). The risk: if crypto prices crash fast enough that liquidations can't keep pace, the system accumulates bad debt. The March 2020 'Black Thursday' crash stressed Maker's system severely. Continuous governance manages collateral ratios, risk parameters, and the stability fee (interest rate for minting DAI).

Algorithmic Stablecoins (Terra/LUNA — R.I.P.)

Algorithmic stablecoins attempt to maintain the peg through supply expansion and contraction driven by arbitrage incentives — no collateral required. Terra's UST/LUNA system was the most prominent example: burn LUNA to mint UST, burn UST to mint LUNA. This works when the system is growing; it collapses in a 'death spiral' when confidence breaks. The May 2022 Terra collapse erased $40B+ in market cap in 48 hours. Pure algorithmic stablecoins have been widely abandoned.

Partially Collateralized (FRAX)

FRAX pioneered a fractional reserve model — partially backed by USDC, partially by its governance token FXS. The collateral ratio adjusts based on market confidence. When demand is high and peg is strong, it reduces the collateral ratio to be more capital-efficient. When peg weakens, it increases the ratio. Currently FRAX has moved toward 100% backing — the hybrid approach was controversial.

For Builders: Which Stablecoin to Use?

For most DeFi protocols, USDC is the default (most liquidity, widest adoption, Circle's regulatory track record). DAI is used where decentralization matters and censorship resistance is important. Avoid building a core product that depends on a less-proven stablecoin. Diversify where possible — accept multiple stablecoins to reduce single-issuer risk.