Circle's stablecoin is pinned to $1 — its stock is pinned to interest rates

In June 2025, Circle Internet Group became the first stablecoin issuer to go public, listing on the NYSE under the ticker CRCL. The stock priced at $31, opened at $69, and closed its first day at $83, a 168% pop that put one of the year's loudest IPOs at a valuation around $17 billion. Circle's product is USDC, a "stablecoin" engineered to be worth exactly one US dollar, always. Which raises an obvious question: how is a company that sells a token designed never to move worth $17 billion, and why does its stock lurch around so much?

The answer runs through three corners of the curriculum at once: digital assets, money markets, and reinvestment risk.

What a stablecoin actually is

A stablecoin is a token pegged to a reference asset (here, the US dollar), and the credible ones hold the peg by being fiat-collateralized: fully backed by reserves. For every USDC outstanding, Circle holds about a dollar of reserves. Those reserves are not cash in a vault; the bulk sit in a regulated government money market fund, invested in short-term US Treasury bills. So a digital dollar that lives on a blockchain is, underneath, a claim on short-term US government debt.

The lesson: a stablecoin is only as stable as its reserves. Back a token with risky or illiquid assets and the peg can break, as several thinly-backed and algorithmic "stablecoins" did. USDC's reserves are deliberately conservative, holding only Treasury bills and cash.

The float: where the money is

This is the part the IPO frenzy was really pricing. Circle earns the interest on those reserves. With roughly $60 billion of USDC outstanding, it holds tens of billions in Treasury bills, and at the rates of 2024–2025 those bills threw off enormous income — interest made up about 99% of Circle's revenue. The users hold a token that pays them nothing, and Circle keeps the yield on the dollars backing it.

This is the float, the same mechanism that makes an insurer profitable on money it holds but will eventually owe out. Circle's float just happens to be tokenized.

Why the stock swings on interest rates

If almost all of Circle's revenue is the interest earned on Treasury bills, then Circle's earnings rise and fall with the level of short-term rates. Those bills mature constantly and are reinvested at whatever rate prevails, so when the Fed cuts, the income reprices downward within weeks — by the company's own disclosure, a one-percentage-point cut could erase roughly $620 million of annual revenue. That is reinvestment risk: the bonds do not lose value, but the cash they throw off shrinks. The token is pinned to a dollar, while the business is a concentrated bet on the level of short-term rates.

That is why a "stable" company trades like anything but. Buy the stock and you are betting on the Fed, and on whether USDC can grow fast enough to replace the income that falling rates take away.

What to take away

Three parts of the curriculum meet in this one company: a digital asset defined by what backs it, the Treasury bills and money-market instruments that do the backing, and the reinvestment risk of a portfolio that reprices every few weeks as those bills roll over. A question will not ask whether Circle is a buy. It will ask you to know that a fiat-collateralized stablecoin is only as safe as its reserves, and that income earned on rolling short-term bills falls when rates do.

The token holds its value, but the reserves behind it earn interest that rises and falls with rates. The "stable" in stablecoin refers to the coin, not to the company that issues it.