Yen Hits 40-Year Low: The Real Reason Behind the First U.S.-Japan Coordinated Intervention in 15 Years — Protecting U.S. Treasuries

164: The Most Dangerous Number in 40 Years

The yen touched 164 against the U.S. dollar in July 2026, its lowest level since November 1986. For years, analyzing yen depreciation required looking at essentially one line: the spread between U.S. dollar interest rates and yen interest rates. The correlation between this spread and the exchange rate was remarkably high over the long term. As long as the Federal Reserve kept rates elevated and the Bank of Japan raised rates at a glacial pace, the yen was supposed to fall, and that was supposed to be the end of the story.

But this time is different. The program pointed out that when you extend the chart of the interest rate differential against the yen exchange rate to the most recent period, this “perfect correlation” collapses dramatically. The rate differential is no longer the dominant factor. In its place is a curve that had previously drawn little attention: the spread between 2-year and 10-year Japanese government bond yields — in other words, the market’s pricing of Japan’s fiscal risk. The logic chain runs as follows: the market loses confidence in the Japanese government’s fiscal discipline, so investors dump long-term JGBs, long-end yields rise, the yield curve steepens, and simultaneously the yen is sold off. Yen depreciation and a narrowing U.S.-Japan rate differential occur at the same time because they are no longer cause and effect — they are two symptoms of the same underlying disease.

That disease sits in the office of Japan’s Prime Minister, Sanae Takaichi.

Takaichi’s “Responsible Active Fiscal Policy” — The Market Votes with Its Feet

Sanae Takaichi is a faithful heir to Abenomics. Her policy direction since taking office has been extremely aggressive: a ¥21 trillion stimulus package and cuts to food consumption taxes. The problem is that during the Abe era, Japanese interest rates were near zero, so the government could borrow heavily without much pressure. But now rates and inflation have both risen, Japan’s government debt is already the highest in the world, and conventional logic would call for raising revenue and cutting spending. Takaichi has done the exact opposite. As the program put it, she is “spending money like there’s no tomorrow while simultaneously cutting taxes aggressively.”

She gave this approach an artfully packaged name — “responsible active fiscal policy.” But the market is not buying it at all. Investors began dumping long-term Japanese government bonds for a very direct reason: with Japan’s fiscal trajectory looking like this, JGBs are starting to look unreliable. This directly spawned Wall Street’s famous “Takaichi Trade”: short JGBs, short the yen, long Japanese equities. This year’s market performance — long-term bonds crashing, the yen crashing, Japanese stocks hitting record highs — maps perfectly onto this trade logic.

The program also drew an unsettling historical parallel: in 2022, UK Prime Minister Liz Truss pushed through massive tax cuts amid intense inflationary pressure, causing the pound and gilts to crash together, and she was out of office in 49 days. Japan is replaying this script, just at a slower pace.

Japan’s Spending Logic: Why Throw ¥25 Trillion at a Problem When the Effect Is Known to Be Limited?

Faced with a collapsing yen, Japan had a “standard solution” available — raising interest rates. But Japan is already raising rates, and it cannot raise them too aggressively without choking the economy. The more fundamental problem is this: what is driving the yen lower is government credibility, and the government is unwilling to cut spending to protect that credibility. The only option left is direct market intervention.

The G7 has a gentleman’s agreement: intervention should be a last resort, and when it happens, members must give advance notice. Japan has a standard script before every intervention: “We are deeply concerned about excessive yen volatility and do not rule out any options.” From 2022 to 2025, Japan spent a total of ¥25 trillion (approximately $160 billion) propping up the yen, and the spending has only accelerated — estimated official spending in 2026 to date has already exceeded ¥25 trillion, matching the combined total of previous years. That figure is roughly one-third of the Japanese government’s total annual revenue.

As the table shows, the scale of monthly intervention has grown more than fivefold in three years, confirming the program’s observation that Japan is “spending more and more with diminishing returns.”

But the effectiveness of intervention is declining. The program used an analogy: this is no longer “boiling a frog in warm water” — the water is starting to bubble.

So why keep intervening? The program’s answer is both simple and resigned: “If someone is in poor health and difficult to cure, do you just say, well, no point taking medicine, no point treating it, since it can’t be cured anyway? No, you wouldn’t. Japan’s situation is actually pretty similar.” The point of intervention is that you “can’t just give up” — it signals to speculative capital that “I’m still here defending this line,” deterring them from taking on excessive leverage.

The Real Reason the U.S. Stepped In: Protecting U.S. Treasuries, Not Protecting a Friend

The United States broke a 15-year precedent (the last time being the 2011 Fukushima nuclear disaster) to intervene jointly. The official line was that “Japan is our good friend and partner.” The program was blunt: “How could that possibly be the reason.”

Note: More precisely, this was the first time since 1998 that the U.S. and Japan jointly bought yen. The 2011 episode, while also a coordinated intervention between the two countries, went in the opposite direction — after the Fukushima disaster, the yen briefly appreciated excessively, and the G7 jointly sold yen to push the exchange rate down, the opposite of this time’s yen-supporting operation.

The real reason is a simple chain of interests:

Japan needs to sell dollars and buy yen to prop up its currency. Most of Japan’s foreign exchange reserves are invested in U.S. Treasuries — Japan is the largest foreign creditor of the U.S. government. To get dollars, Japan has to sell U.S. Treasuries first. And what U.S. Treasury Secretary Scott Bessent fears most is precisely a sell-off of U.S. Treasuries by the largest creditor.

Bessent said publicly last year that the most important KPI of his job is the U.S. 10-year Treasury yield. This year has already been rough for him on that front — Treasury yields have stubbornly refused to come down — and the last thing he needs is Japan adding fuel to the fire. So the most direct and primary motive for the U.S. stepping in to help Japan is protecting the U.S. Treasury market. The program also mentioned other secondary reasons — protecting tariff effectiveness (not wanting an overly weak yen and overly strong dollar to widen the trade deficit) and preserving Takaichi’s political stability — but all of these rank behind U.S. Treasuries.

Sticky Notes, FIMA, and That Goldman Sachs Trade Ticket Caught on Camera

At 10:30 p.m. Japan time on July 30, 2026, the Japanese government began buying yen, and the currency surged. That day, when Japan’s top currency official was asked whether the U.S. was involved, he gave a cryptic answer: “The support we received from the United States went beyond the psychological level.” The next day, media captured a to-do item in Bessent’s notebook: “Buy yen $5–10 billion,” written in large, clear letters with an underline. The host joked: “You can’t even tell if he deliberately showed it to the media.”

It was subsequently confirmed that the New York Fed, acting on behalf of the Treasury, sold euros and bought yen through Goldman Sachs and Morgan Stanley. Why sell euros instead of dollars? The program explained that the U.S. didn’t want to send a signal that it was “intervening in the dollar,” nor did it want to sell dollars, so it sold off the small amount of euros it had on hand. Europe took collateral damage, while South Korea “rushed over to join the party” — the Korean won had just hit a 17-year low in June, and South Korea seized the opportunity of the U.S.-Japan joint intervention to support the won, hoping to ride the coattails.

America’s real “trump card” was the second move: the FIMA Repo Facility (Foreign and International Monetary Authorities Repo Facility). This tool was launched by the Federal Reserve during the pandemic and is essentially a “central bank version of a collateralized loan” — foreign central banks can pledge U.S. Treasuries held in custody at the New York Fed as collateral to borrow dollars overnight from the Fed, and can keep rolling the loans indefinitely. The program noted that this tool had rarely been used before; the largest instance was in 2023 when Credit Suisse imploded and the Swiss National Bank urgently pledged U.S. Treasuries to borrow $60 billion to keep the bank alive.

The key point this time: Japan hasn’t actually used this facility yet, but Bessent publicly signaled to the market that he “encourages Japan to use it,” and Japan responded that it “will definitely use it in the future.” The mere exchange of public statements between the two sides was enough to scare off a wave of speculative capital shorting the yen. The deterrent power of this tool lies in the fact that Japan could theoretically pledge its entire foreign exchange reserves — over $1 trillion — giving it effectively unlimited ammunition.