Stablecoin Design Tradeoffs: Fiat-Backed vs Algorithmic vs CDP — Where Each Breaks

Stablecoins are not a solved problem. That sounds strange given how much capital flows through them, but the three main design approaches each have structural failure modes that the industry hasn't eliminated — only mitigated, managed, or, in some cases, ignored.

## Fiat-backed: the simplest model and its constraints

USDC and USDT are the dominant examples. The design is simple: each token represents a claim on one dollar (or equivalent) held in reserve by the issuing company. The peg is maintained by arbitrage — if USDC trades below $1, arbitrageurs buy it and redeem for dollars; if it trades above, they mint new USDC by depositing dollars.

*The trust assumption is almost entirely legal.* Users trust that Circle or Tether holds the reserves they claim, that those reserves are accessible when needed, and that the issuing entity is solvent and compliant with the regulatory environments that govern redemption.

USDC's March 2023 depeg illustrates where this breaks. When Silicon Valley Bank failed, Circle had $3.3 billion of USDC reserves deposited there. Before the weekend FDIC resolution, USDC traded as low as $0.87. The peg broke not because of crypto mechanics but because of banking system risk that Circle had introduced through its reserve management choices. The peg recovered when federal deposit insurance covered the SVB balances. That recovery was a policy decision, not a cryptographic guarantee.

Tether's risk profile is different. Questions about the composition and auditability of Tether's reserves have been present since 2017. Tether has never undergone a full independent audit in the conventional financial sense. The company has consistently maintained the peg through what appears to be adequate liquidity management, but the reserve opacity means the peg's robustness cannot be independently verified.

## Algorithmic: what it tried to do and where it actually fails

The appeal was genuine: a stablecoin that maintains its peg without any external collateral, using algorithmic supply expansion and contraction instead. The theoretical mechanism is that a second token absorbs the volatility — when the stablecoin is above peg, the system mints more; when below peg, the system buys back using the second token.

UST/LUNA is the dominant case study. At peak, UST had $18 billion in circulation and LUNA had a market cap of around $40 billion. The depeg triggered a bank run dynamic: UST holders rushed to sell, the algorithm minted LUNA to absorb selling pressure, LUNA's price declined, the algorithm minted more LUNA, which declined further — hyperinflation in the second token, collapse of both. $40 billion evaporated in about a week in May 2022.

The fundamental problem wasn't a code bug. It was the design: the stability mechanism is circular. The second token's value depends on faith in the stablecoin, and the stablecoin's stability depends on the second token having value. Under stress, that circularity collapses.

This doesn't mean algorithmic stablecoins are inherently impossible, but it does mean that mechanisms that rely on reflexive confidence rather than overcollateralization are structurally fragile under coordinated selling pressure.

## CDP: overcollateralization as the design principle

MakerDAO's DAI is the canonical example. Users deposit ETH (or other accepted collateral) into a Collateralized Debt Position, and DAI is minted against it at overcollateralized ratios — typically 150% or higher. If collateral value drops below liquidation thresholds, the position is liquidated automatically. The excess collateral buffers against peg failure.

The peg stability mechanism is the DAI Savings Rate — an interest rate that Maker governance sets to make holding DAI more or less attractive, adjusting demand for the stablecoin.

Where CDP designs fail: if collateral prices drop faster than liquidations can process them, the system can accumulate bad debt. On Black Thursday in March 2020, ETH dropped 50% in hours. Ethereum network congestion made liquidations extremely expensive; some liquidation auctions cleared at 0 DAI for ETH collateral because no one could get a competing bid on-chain in time. MakerDAO socialized the bad debt through an emergency auction of MKR governance tokens.

The more interesting evolution is what MakerDAO has become since: roughly 60% of DAI's collateral is now real-world assets — US Treasury bills held through institutional frameworks. This significantly improved yield (DAI holders got the DSR at nearly 8% at points in 2023–2024) but introduced traditional financial system risk back into what was designed as a trustless mechanism.

> **Key Takeaway:** Each stablecoin design trades one set of failure modes for another. Fiat-backed stablecoins are exposed to issuer solvency and reserve management quality. Algorithmic designs are exposed to reflexive collapse under stress. CDP designs are exposed to oracle failure, liquidation mechanics, and the collateral risk of whatever they accept. Understanding which risks you're accepting matters more than assuming the peg will hold.

Stablecoin Design Tradeoffs: Fiat-Backed vs Algorithmic vs CDP — Where Each Breaks

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