<div id="readability-page-1"><div id="ArticleBody-InlineImage-108155408"><div><div><p>Traders work on the floor at the New York Stock Exchange on the day of Circle Internet Group's initial public offering on June 5, 2025.</p><p>Brendan McDermid | Reuters</p></div></div></div><div><p>Stablecoin issuer <span id="RegularArticle-QuoteInBody-1">Circle<span><span id="-WatchlistDropdown"></span></span></span> is tumbling after competitor Tether announced it has hired an unnamed Big Four accounting firm to audit its <span id="RegularArticle-QuoteInBody-3">USDT<span><span id="-WatchlistDropdown"></span></span></span> reserves for the first time.</p><p>The shares were last down by 19%, marking the stock's worst day ever. Previously, its steepest dive was June 27, when it sunk 15.5%. </p><p>USDT is the largest stablecoin in the market with $184 billion in market cap, according to CryptoQuant. However, it has been mired in controversy for years because Tether promised transparency through quarterly &#34;attestations&#34; but has never provided a full, formal audit. That made many investors and regulators worried that USDT reserves were too opaque or would not meet audit standards.</p><p>Stablecoins are cryptocurrencies that peg their prices to an underlying asset, usually the U.S. dollar, and are often backed by dollar deposits, short-term U.S. Treasurys and similar cash equivalents. As they're designed to be less volatile than most cryptocurrencies, audits help ensure the stability is really there.</p><p>&#34;The engagement of a Big Four underscores its commitment to providing deep assurance that USDT is fully backed, highly liquid, and operated with world-class risk management,&#34; the company said in a statement. &#34;By formally engaging a Big Four audit firm, Tether is taking one of the most important steps, strengthening its position as the global leader in transparency, assurance, and regulatory readiness.&#34;</p><p>The move also dragged down <span id="RegularArticle-QuoteInBody-4">Coinbase<span><span id="-WatchlistDropdown"></span></span></span>, which is the main distribution platform for USDC. Shares were last down 9%.</p><p>Circle surged in popularity last year following its successful IPO, and its <span id="RegularArticle-QuoteInBody-7">USDC<span><span id="-WatchlistDropdown"></span></span></span> coin is widely viewed as more institutional grade than Tether as it undergoes full audits annually by Deloitte and also issues monthly attestations. USDC is the second largest stablecoin with a market cap of $78.6 billion.</p><p>Tether's USDT was created in 2014 to be pegged to the value of the U.S. dollar and was the only stablecoin on the market for years before U.S.-regulated alternatives like Circle's USDC cropped up. It has remained the most popular and dominant stablecoin despite controversy and regulatory scrutiny over the years.</p><p>Stablecoins including USDT have been primarily for trading and as collateral in decentralized finance (DeFi). Crypto investors watch them closely for evidence of demand, liquidity and activity in the market. In the past year, however, banks, fintech companies and other brands have been drawn to their ability to move dollars quickly and cheaply across borders.</p><p><em>—CNBC's Nick Wells contributed reporting.</em></p></div><div><p>Choose CNBC as your preferred source on Google and never miss a moment from the most trusted name in business news.</p></div></div>

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<p>Circle's stock is experiencing its worst day ever, plummeting 19% after Tether announced it has engaged a Big Four accounting firm for a full audit of its USDT reserves. This move aims to enhance transparency and address concerns over USDT's backing. Tether's USDT remains the largest stablecoin, while Circle's USDC, which undergoes annual audits, is viewed as more reliable. The news also negatively impacted Coinbase's shares, which fell 9%.</p>

- Circle's stock plummeted 19% after Tether announced it is hiring a Big Four accounting firm to audit USDT reserves for the first time.  
- USDT, with a market cap of $184 billion, has faced scrutiny for its lack of full audits, raising concerns among investors and regulators.  
- This news also negatively impacted Coinbase, while Circle's USDC, viewed as more stable due to its annual audits, remains the second largest stablecoin with a market cap of $78.6 billion.

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Circle heads for its worst day on record as stablecoin rival Tether announces audit milestone