What a stablecoin actually is
A stablecoin is a crypto token engineered to track a stable asset — almost always the US dollar. One token aims to equal $1, always. That predictability is what makes everything else possible: traders park value without cashing out to banks, DeFi protocols price loans in dollars, and AI agents settle micropayments without repricing every API call (see How AI Agents Pay Each Other).
The entire design question is: what makes the $1 credible? The answers split stablecoins into three families.
The three designs
1. Fiat-backed (USDC, USDT)
The issuer holds dollars (or Treasury bills) in reserve and mints one token per dollar. Redemption is the peg’s anchor: if the token ever trades at $0.99, traders buy it cheap and redeem it for $1. The risk is counterparty trust — you’re trusting the issuer’s reserves, audits, and honesty.
2. Crypto-backed (DAI)
The token is backed by other crypto locked in smart contracts, over-collateralized to absorb volatility (e.g., $1.50 of ETH backing $1 of DAI). No bank account needed — but the peg depends on the collateral holding value and the contracts working as designed.
3. Algorithmic
No meaningful reserves; the peg is maintained by code that expands or contracts supply. This is the design with the worst track record — see below.
“Stable” describes the target, not a guarantee. Every stablecoin is a mechanism plus a promise. Understand both before trusting either.
Where pegs have broken
The cautionary tale is TerraUSD (UST), an algorithmic stablecoin that collapsed in May 2022, wiping out roughly $40 billion in value in days. Its sister token LUNA entered a death spiral as the peg-defense mechanism itself became the attack vector. The lesson the industry took: a peg defended only by incentives, with no exogenous collateral, is fragile under stress.
Even fiat-backed coins have wobbled — USDC briefly traded below peg in March 2023 when its banking partner failed — but reserve-backed designs have recovered where algorithmic ones died.
Why agents settle in stablecoins
Machine payments need unit-of-account stability. A server charging $0.003 per API call can’t reprice in a token that moves 5% an hour. Stablecoins give agents dollar-denominated money with crypto’s programmability: holdable by software, sendable in seconds, divisible to fractions of a cent. That’s why the x402 rails and their cousins settle in stablecoins, not in volatile tokens.
Regulation is catching up: the GENIUS Act
In the US, the GENIUS Act established the first federal framework for payment stablecoins — reserve requirements, issuer licensing, and consumer protections. As of October 2026, regulators including the US Treasury are still writing the detailed rules. The direction is clear: stablecoins are being pulled inside the regulatory perimeter, which should reduce issuer risk over time but may also narrow which coins qualify and where they can be used.
Risks, plainly
- Depeg risk: the token can trade below $1 under stress. Backing quality determines whether it recovers.
- Issuer & custody risk: fiat-backed coins depend on the issuer’s reserves and banking access.
- Smart-contract risk: crypto-backed designs depend on code. Code has bugs.
- Regulatory risk: rules are still being written; compliant-today doesn’t guarantee compliant-tomorrow in every jurisdiction.
- Concentration: two issuers dominate the market. A problem at either one is a systemic event.
Key terms
Educational content only — not financial advice. Do your own research.