Fiat-backed stablecoins are the most mainstream <a href="https://crypto-bible.com/en/glossary/defi-basics/stablecoin/" target="_blank">Stablecoin</a> type: issuers hold equivalent fiat currency (usually USD) or highly liquid assets (like short-term Treasuries) in banks or custodians, and must have corresponding reserves for every coin issued. Users can redeem stablecoins for fiat 1:1 at any time. USDC and USDT are the two largest fiat-backed stablecoins by circulation. Their advantage is high price stability and an intuitive mechanism; the core risk lies in trust in the issuer — whether reserves are real and sufficient depends entirely on issuer integrity and audit transparency.

Reserve ratio is the proportion of actual reserve assets held by a <a href="https://crypto-bible.com/en/glossary/defi-basics/stablecoin/" target="_blank">Stablecoin</a> issuer relative to the total supply of stablecoins in circulation. A ratio of 100% means every circulating stablecoin is backed by equivalent real assets; below 100% indicates an over-issuance risk — if all holders redeem simultaneously, the issuer may be unable to pay in full. Reserve ratio is one of the most direct indicators for assessing the health of a fiat-backed stablecoin, but the ratio alone is just the starting point: the quality and liquidity of reserve assets matter equally.

<a href="https://crypto-bible.com/en/glossary/defi-basics/stablecoin/" target="_blank">Stablecoin</a> yield refers to the annualized interest return obtained by holding stablecoins and depositing them into specific platforms or protocols. Three main sources: centralized platform interest accounts (like Coinbase USDC Rewards, approximately 4-5%), DeFi lending protocols (like Aave, approximately 3-6%, rates floating with borrowing demand), and liquidity provision (like Curve stablecoin pools, approximately 1-5%). The biggest trap with stablecoin yields is 'opaque yield sources': genuinely sustainable yields must come from real lending demand; artificially subsidized high yields (like Anchor Protocol's 20% UST annualized rate) are classic Ponzi structures that ultimately end in system collapse.

The Tether reserve controversy is a long-running transparency dispute surrounding USDT issuer Tether Limited: does Tether genuinely hold sufficient real assets for every USDT to be redeemed 1:1? This question has troubled markets since 2017. Core events include: a 2021 CFTC investigation (finding Tether had insufficient reserves during some periods and held large amounts of commercial paper) with a $41M settlement; multiple auditor changes; and Tether's continued refusal to accept a complete audit from a major international Big Four accounting firm. In recent years Tether has substantially improved (shifted to Treasuries), but the controversy's history and relative transparency shortfall remain important context for assessing USDT risk.

USDC is a fiat-backed <a href="https://crypto-bible.com/en/glossary/defi-basics/stablecoin/" target="_blank">Stablecoin</a> issued by Circle Internet Financial. Every USDC is backed by equivalent USD cash or short-term US Treasuries held at regulated custodians. Circle publishes monthly Deloitte-attested reserve verification reports and holds money transmission licenses across multiple US states plus EU EMI licenses (MiCA compliant). As of 2026, USDC has approximately $76 billion in circulation — currently the most transparent and regulatory-compliant mainstream USD stablecoin, and the standard stablecoin choice in the Coinbase ecosystem and European markets.