The US Treasury just pulled off something it hasn’t done in more than ten years: a coordinated currency intervention with Japan. Instead of selling dollars to buy yen, which is the conventional playbook, Treasury Secretary Scott Bessent opted to sell euros. The goal was straightforward: shore up Japan’s battered currency without weakening the greenback in the process.

What actually happened

The operation took place over July 31 and August 1, 2026, with the Federal Reserve Bank of New York executing the trades. Goldman Sachs and Morgan Stanley handled the execution, selling euros to purchase Japanese yen on behalf of the US government.

A handwritten note from Bessent’s Camp David notepad, which surfaced in reporting on the intervention, revealed the planned scale: between $5 billion and $10 billion worth of yen purchases.

The results were immediate. The yen strengthened by more than 1% against both the US dollar and the euro on the day of the coordinated action.

Bessent described the yen as “very undervalued,” framing the intervention as a response to what he characterized as unhealthy volatility rather than an attempt to engineer a specific exchange rate. The yen had been trading near 40-year lows heading into the operation, battered by persistent interest rate differentials between the US and Japan.

Why euros instead of dollars

Using euro reserves instead of dollars accomplishes two things simultaneously. It supports the yen by creating buying pressure, and it avoids putting downward pressure on the USD. The euro takes the hit instead.

The $5 billion to $10 billion deployment is also worth contextualizing. Japan’s own foreign exchange reserves exceed $1 trillion. The US contribution, while symbolically important, represents a fraction of what Japan could deploy unilaterally. The real value here is the signal: the US is willing to co-sign Japan’s currency defense.

The crypto and macro connection

The Japanese yen carry trade has been one of the most important macro dynamics affecting risk assets, including crypto, for years. Investors borrow cheaply in yen and deploy that capital into higher-yielding assets elsewhere. When the yen suddenly strengthens, those trades unwind, sometimes violently. The August 2024 yen carry trade unwind sent shockwaves through equity and crypto markets alike, with Bitcoin dropping sharply as leveraged positions got liquidated.

The decision to use euro reserves rather than dollar reserves raises questions about the future composition of US foreign exchange holdings. If the Treasury is willing to draw down euro positions to defend allied currencies, that changes the calculus around reserve management.

For investors watching the dollar index, the intervention’s structure is actually bullish for USD in the near term. By avoiding direct dollar sales, Bessent preserved dollar strength while still accomplishing the policy objective.