Are stablecoins really stable? What USDT and USDC each have behind them

Short version: a stablecoin is a crypto asset pegged 1:1 to the US dollar. One USDT is supposed to equal one dollar. One USDC is supposed to equal one dollar. That sounds simple — but the word "pegged" hides an entire financial machine underneath, and the machine has broken several times in the last decade. Each time it broke, somebody got wiped out. This piece walks through the four mainstream stablecoins, two well-known failures, and where regulation is heading.

§1 · Why do stablecoins exist at all?

BTC and ETH can swing hard in a single day. Nobody is going to pay rent in something that might be much cheaper by Friday. Nobody is going to do payroll in an asset that has weekly drawdowns the size of a small recession. So crypto needed a price-stable settlement layer, and the dollar was the obvious choice because the dollar is what people already think in.

Before stablecoins existed, the only way to take risk off the table was to wire money back out to a bank. That process is slow, expensive, and pinched at every customs checkpoint between you and the bank — cross-border wires take days, hit foreign-exchange spread, and incur compliance friction at both ends. When Tether launched USDT in 2014, the breakthrough was simple but powerful: your dollars could stay on-chain, ready to flip back into BTC the moment you wanted to re-enter. That single innovation is what made 24/7 global crypto trading actually fluid.

Today stablecoins are the bloodstream of the entire market. Aggregate stablecoin supply is about $312.3B (DefiLlama, September 25, 2026). Most spot trading pairs on major exchanges are quoted in stablecoins rather than fiat. If you have spent more than a week buying or selling crypto, you have touched one — even if you did not know it.

§2 · Four stablecoin types, four very different peg mechanisms

Type 1 · Fiat-reserve-backed (USDT, USDC, FDUSD, PYUSD)

The most direct model. The issuer takes in one dollar, mints one token. When you redeem, the token is burned and a dollar is wired back to you. Behind the token there is supposed to be an actual dollar, or a dollar-equivalent asset like short-duration US Treasury bills, sitting in a regulated banking partner. USDT, USDC, FDUSD and PayPal's PYUSD all use this design.

The risks are easy to enumerate but harder to defend against:

• Are the reserves real? Tether was hammered for years on suspicion of under-collateralization, and while no large failure has materialized, the audit standard remains looser than USDC's.
• Is the banking partner safe? This is exactly what blew up USDC in March 2023 — more on that in a moment.
• Regulatory action: a US authority can freeze the issuer's accounts, and the issuer can freeze your token at the smart-contract level. USDT and USDC both have on-chain blacklist functions, and both have frozen substantial amounts this way, including at law-enforcement and OFAC request.

Type 2 · Over-collateralized crypto-backed (DAI / sDAI / USDS)

DAI, issued by MakerDAO (now rebranded to Sky), takes the opposite approach. There is no bank account. Instead, you lock 150% (or more) of dollar value in ETH or other crypto into a smart contract and the protocol mints you 100 dollars of DAI. If your collateral falls below the threshold, the protocol forcibly liquidates it.

Advantages: every dollar of backing is on-chain, instantly verifiable by anyone with a block explorer. No bank, no jurisdictional risk. Disadvantages: capital-inefficient (you tie up $1.50 to use $1.00), and during violent price moves the liquidation mechanism can fail mechanically — as it did during the March 12, 2020 crash, when gas prices spiked so high that many liquidation bots failed to bid, and some vaults' collateral was won with zero-DAI bids.

Type 3 · Algorithmic stablecoins (USTC, dead)

The most dangerous category. There is no external collateral at all. The peg is held entirely by algorithmic mint-and-burn loops with a sister token, and by arbitrageurs being willing to step in. The textbook failure is Terra's UST (now renamed USTC because it collapsed). That model has been tried dozens of times and has failed dozens of times — Iron Finance, Beanstalk, Basis Cash all went to zero in different mechanical ways. UST was just the largest, wiping out roughly $40B of paper market cap.

Type 4 · Yield-bearing / synthetic dollars (USDe, sDAI, sUSDS)

A newer category that emerged in 2023-2024. Ethena's USDe is the headline example: it generates a synthetic dollar by combining long spot ETH with an equal-size short ETH perpetual futures position, hedging the price exposure to zero and capturing perp funding rates as yield. The yield is real when funding is positive. When markets dislocate and funding inverts, the yield collapses and the peg can drift. The mechanism is fundamentally a derivatives trading strategy wrapped in a token. New users should not treat these as a savings vehicle.

§3 · How do USDT, USDC, DAI and FDUSD differ?

Put the four side by side: USDT and USDC are both fiat-reserve coins and by far the largest; DAI/USDS is backed by on-chain over-collateralization; FDUSD is much smaller and had a clear depeg in April 2025.

The USDT and USDC market caps are CoinGecko figures as of September 25, 2026. They move daily — pull current data from CoinGecko or DefiLlama if you need it live.

§4 · Lesson 1 · How did UST and LUNA collapse in 2022?

In early May 2022, UST started slipping below $1. For a stablecoin that is supposed to print $1.00 all day every day, $0.98 is already an event.

Over the following days UST fell through $0.60, then $0.30, and finally below $0.10, while LUNA went from around $60 to effectively zero. Roughly $40B of market cap was erased within days.

Riding it down or buying the dip on the logic "this is a peg, it has to come back" would not have saved you. It did not come back. The lesson is blunt: a stablecoin with no real-world reserves is not, in any meaningful sense, stable.

The death spiral, mechanically

The Terra mechanism worked like this: $1 of UST could always be minted by burning $1 worth of LUNA, and vice versa. In theory, arbitrageurs would keep UST pinned to a dollar. The hidden assumption was that LUNA had to have enough market depth to absorb the redemptions.

Once a critical mass of UST holders tried to exit at the same time — triggered by large withdrawals from Anchor Protocol and heavy selling — the system had to mint enormous amounts of LUNA to absorb the redemptions. LUNA supply exploded. LUNA price collapsed. The collapse made breaking the UST peg even cheaper, which sent another wave of redemptions through the system, which minted more LUNA, which collapsed further. Within days the loop completed. Every algorithmic stablecoin with no external collateral has this exact failure mode latent inside it. UST is the case in point: it lost its peg in May 2022, and it and LUNA fell to close to zero (see the SEC's press release 2023-32).

§5 · Lesson 2 · Why did USDC lose its dollar peg in March 2023?

Friday, March 10, 2023. Silicon Valley Bank was placed into FDIC receivership — one of the largest US bank failures since the 2008 financial crisis. Circle had roughly $3.3 billion of USDC reserves parked at SVB. That was disclosed Friday night.

Over the weekend, with US banking closed, the on-chain market did the only thing it could: it priced the uncertainty. USDC fell from $1.00 to $0.87 — a 13% depeg, the deepest in USDC's history.

If your first instinct was to swap into USDT — USDT had its own transparency questions, so it was not obviously the safer place to run to. Those who dumped USDC at the bottom of the panic locked in a loss that would otherwise have disappeared.

Before the weekend was over, US regulators announced that SVB depositors would be made whole, including uninsured deposits. Circle's $3.3B was fully recoverable, and USDC soon traded back to around $1.00.

What this episode teaches

There is no such thing as an "absolutely safe" fiat-backed stablecoin. Reserves can be transparent, audited, and properly held — but the moment they are deposited at a specific bank, you inherit that bank's risk. Circle was lucky in March 2023. The US government intervened. Next time the political environment might be different, or the bank involved might be too small to warrant intervention.

The more robust approach is to diversify across stablecoins rather than bet on any single issuer: a slice in USDT (deepest liquidity, fewest gas pain points), a slice in USDC (highest compliance, best regulated-banking rails), and a small slice in DAI/USDS (on-chain transparency as a hedge against off-chain failure). Concentration in one stablecoin is a category of risk most retail underestimates.

§6 · Small amounts, mid-sized, large amounts — what to do

Small daily amounts (a few hundred to a few thousand dollars)

USDT or USDC both work. Pick whichever your exchange supports with the lowest fees and deepest liquidity. Do not assume any one network is the cheapest: USDT-TRC20 (Tron network) transfers consume energy or burn TRX, and exchanges adjust their per-network withdrawal fees often, so compare them on the withdrawal page. USDC on Solana or Base is usually cheap and fast.
Avoid: sending small amounts on Ethereum mainnet. When the network is busy, a single transaction's gas can eat a big chunk of a small transfer.

Mid-sized balances (a few thousand to a few tens of thousands)

Split it. Half USDT and half USDC, on different chains. If one issuer hits a regulatory event or one chain has a temporary outage, you still have access to the other. Keep it on tier-one venues that are available and properly licensed where you live — not on small offshore exchanges. The FTX lesson should be permanent: do not park meaningful balances at exchanges you cannot independently verify the solvency of.

Large balances (six figures and above)

Diversify further across USDC, USDT and DAI/USDS so a single-issuer event does not wipe you. Do not park large balances at any exchange. Move to your own hardware wallet — Ledger or Trezor — and treat the seed phrase like the only copy of a will. If you want to earn yield on idle balances, mature DeFi lending markets like Aave or Compound v3 are the options, but every smart contract carries non-zero hack risk, so cap the percentage: keep only as much of your stablecoins in DeFi as you could lose without real damage.

§7 · Where the regulation is going

Stablecoin regulation has gone from non-existent to one of the most actively worked areas of crypto law in less than three years. In the US, the GENIUS Act, signed into law in July 2025, created the first federal payment-stablecoin regime. NYDFS continues to operate the state-level model for trust-chartered issuers. On the EU side, MiCA is now fully operative. Stablecoin issuers either comply or lose access to regulated venues. Hong Kong's Stablecoins Ordinance, in force as of 2024-2025, creates an HKMA-licensed regime for issuers.

The longer-term trajectory is clear. Compliant, audited, fiat-backed stablecoins — USDC, PYUSD, GUSD, the emerging EUR-denominated set — become the default rail for retail and institutional payment use cases. USDT will likely keep dominating trading-pair liquidity for years because the on-chain network effect is hard to dislodge, even as some regulated markets restrict it. Pure algorithmic stablecoins have, as far as I can tell, no future in a regulated world — the math has failed every time and the regulators have noticed.

§8 · Closing thoughts

Stablecoins are not "automatically stable." They have a peg mechanism, reserve risk, counterparty bank risk, smart-contract risk, and regulatory risk. Any one of those can turn your "stable" position into a loss.

Three rules I would put in front of any new stablecoin holder:

1. Diversify holdings. USDT and USDC both. Maybe a slice in DAI or USDS. Do not concentrate in any single issuer, no matter how good the recent attestation looked.
2. Do not park at small exchanges. Large balances go to self-custody. Small operational balances stay at tier-one regulated venues.
3. Avoid high-yield stablecoin products. The reasonable yield range is 3-8% in the current rate environment. Anything above that is buying you risk you almost certainly cannot price.

If your next step is going to be DeFi, stablecoins are going to be the tool you reach for every day. Read the DeFi piece next.