Circle froze a Tether-backed fund over manipulation fears

Circle suspended Heka Funds, an arbitrage trading firm, after discovering Tether had invested $800 million into it, according to arbitration filings reviewed by The Block. Circle flagged suspected market manipulation tied to the fund and cut it off before the dispute escalated into arbitration.

What the filings show

The headline number is $800 million: that's the size of Tether's stake in Heka Funds, per the filings. Circle's own concern was manipulation risk large enough to warrant suspending the relationship rather than working it out quietly. Arbitration filings exist because a suspension of that size doesn't happen without a fight, someone disputes it, and the dispute lands in a formal process rather than a phone call. No dollar figure has been disclosed for what Circle itself had at stake through Heka, and there's no public confirmation yet of what specific trading activity triggered the manipulation concern. The filings establish the sequence: Tether's $800 million position becomes known to Circle, Circle suspends the fund, arbitration follows. That's the concrete record so far.

Why a stablecoin issuer parks money with a trading fund at all

Stablecoin issuers sit on enormous reserve balances that need to earn yield somewhere beyond just Treasury bills, and arbitrage funds are a common outlet for that cash because they promise market-neutral returns without directional risk. Tether putting $800 million into one such vehicle isn't unusual in scale, Tether's reserves run into the tens of billions and it has a track record of parking capital across a wide range of instruments and counterparties, some of which have drawn scrutiny before.

What's notable here is the other side of the trade. Circle is Tether's chief rival in the stablecoin market, and Circle is the one that pulled the plug on a fund Tether had bet $800 million on, over suspected manipulation. That's not a routine counterparty dispute. It reads as one issuer's risk team catching signals in a shared trading relationship that its competitor's capital was sitting inside, and deciding the exposure wasn't worth carrying. Whether Circle believed the manipulation concerned USDC-related markets, general crypto arbitrage strategies, or something else entirely isn't spelled out in what's public, but the decision to suspend rather than simply monitor tells you Circle's compliance bar for this relationship got crossed hard enough to risk litigation.

The bigger point is structural. Both major stablecoin issuers were apparently exposed, directly or through overlapping counterparties, to the same trading fund. That's the kind of concentration risk that doesn't show up in reserve attestations, which report what assets back the stablecoin, not what happens to the yield-generating side deals issuers run alongside those reserves. An $800 million allocation from one issuer sitting next to whatever Circle had committed, in a fund now accused of manipulation, is a reminder that reserve transparency reports don't capture this layer of the business at all.

What comes next

Watch whether the arbitration filings become public in full, or whether a settlement seals the record before anyone learns what the manipulation allegations actually were. If Tether discloses its own response, or if Heka Funds surfaces in other counterparty disputes, that would confirm this was a systemic problem with the fund rather than a narrow disagreement between Circle and one trading partner. Silence from Tether, by contrast, would leave the $800 million figure as the only fixed point in a story that otherwise stays behind closed arbitration doors.