Why the US-Japan Yen Intervention Is Failing

Dear Reader,

There’s a big story going down in FX town that you might not have paid attention to.

On 31 July, the US and Japan spent roughly US$60 billion buying yen.

The yen had hit 163.99 to the US dollar. A 40-year low. Japan’s Ministry of Finance sold roughly US$53 billion of reserves in a single day, buying ¥8.45 trillion with it, and the US Treasury joined with an estimated US$5-10 billion of its own.

That’s the largest one-day intervention Tokyo has ever run.

It moved the pair by nine yen, or about 5%.

By 3 August the currency was at 155.23. A stabilisation in the 140-150 range is probably the ideal in the medium-term. That would be a good compromise between slowing consumer inflation and keeping exporters competitive.

But it didn’t last long.

By 12 August it was all the way back to 159.45. Traders could be selling before 160 under the thesis that it’s the area that will be defended with intervention.

Twelve days. Half the move, gone.

On the surface the story is boring. Drill a bit deeper and it’s confusing. Underneath that, there are some massive warning signs for global markets that you need to be on top of.

The US-Japan yen intervention is failing for one reason.

The interest rate differential.

It’s fighting an interest rate gap that keeps getting wider, and no amount of money fixes a gap that policy is still opening.

Japan wanted this badly. The low yen has been pushing on inflation in Japan, as the price of imported goods increase in local terms. The optics of that are bad for those running the country.

Japan’s had next to no inflation since dinosaurs roamed the earth. The fact that it’s now a non-zero number while wages are stagnant is causing some angst.

Never fear, the Americans are here.

So, is the US just that super friendly neighbour who wanders over to take your bins back inside when you’re away on holidays? Head wedged under the bonnet of your — once again — broken down Kingswood, rejoicing in how it’s way better than newer cars because it doesn’t have aircon, power steering, fuel injection or any of those other modern gadgets that make a car harder to work on, even if it’s only running three days per month.

Well, not exactly.

The US has their own motives. And as you’ve just seen, they haven’t been able to get that car started.

Let’s dig into why that happened, because the answer runs through American technology stocks, Japanese pensioners and a house in the countryside you could buy for the price of a used Hilux.

Why Did the US Buy Yen?

The New York Federal Reserve, acting for the US Treasury, sold euros to buy yen. It didn’t sell dollars.

Washington helped push its own currency down against the yen while going out of its way to avoid touching the dollar or the Treasury market.

This is crucial.

The US doesn’t rescue other countries’ currencies. The last time Washington bought yen alongside Tokyo was 1998, under Robert Rubin, during the Asian financial crisis.

The last joint intervention of any kind was 2011, when the Group of Seven (G7) sold yen after the Tōhoku earthquake.

Fifteen years of nothing. Then this.

From their perspective, the US was protecting the US Treasury market, not the yen.

Japan owns about US$1.14 trillion of US Treasuries. The largest foreign holding on earth.

The lazy version of this story says Tokyo funds its currency defence by selling those bonds, US yields spike, and everyone panics. It’s the fear that shows up every time the yen gets hit.

Watch what happened instead.

Finance Minister Satsuki Katayama announced that Japan will raise future intervention dollars through the Federal Reserve’s Foreign and International Monetary Authorities (FIMA) repo facility. Tokyo pledges Treasuries as collateral and borrows dollars against them, rather than selling.

Then Treasury Secretary Scott Bessent went public and urged the Fed to lift the facility’s cap, currently US$60 billion per counterparty per day.

Sit with that for a second.

The US Treasury Secretary is lobbying his own central bank, in public, to build a bigger lending window so a foreign government can defend its currency without selling American debt.

That’s your answer on motive.

US 10-year yields have travelled from 4.1% at the start of 2026 to about 4.68% now. Washington is running an annual deficit near US$2.1 trillion. Total debt is near US$40 trillion, with net interest costs approaching US$1 trillion.

More than it spends on defence.

The Congressional Budget Office (CBO) expects that interest bill to reach US$2.1 trillion by 2036, with higher average rates responsible for roughly half the increase. Interest alone, a decade from now, matching this year’s entire deficit.

America cannot afford a forced seller in its bond market.

That would mean any expiring debt would need to be refinanced at substantially higher prices. With new debt on top.

Why the Yen Fell Straight Back

Currency intervention works when a market has broken. Spreads blow out, liquidity vanishes, prices stop making sense, and a central bank steps in to restore order.

None of that was happening.

Mark Sobel, the former US Treasury official who now chairs OMFIF’s US operation, made the point bluntly. Trading was orderly. Spreads were normal. The yen at 164 was priced exactly right for the policy Japan is running.

You can’t intervene your way out of arithmetic.

Just ask the Bank of England or George Soros. More on this here.

The Bank of Japan (BOJ) has a policy rate of 1.00%. It hiked in June, the first time Japanese rates had touched 1% since 1995, then held on 31 July, the same day it was buying its own currency.

The US federal funds rate is 3.50% to 3.75%.

That’s a gap of 250 to 275 basis points, and every day it stays open, someone gets paid to borrow yen and own something else. The carry trade.

Sixty billion dollars of intervention doesn’t change the payoff on that trade. It just gives the people running it a better entry price.

Which brings us to the part.

The gap has a heap of potential to get even wider, and the reason is sitting in a data centre in Texas.

The AI Boom Is Setting the Yen’s Price

We talked last week about what ASX earnings season has to prove. And how much of the local market’s fate is decided in America. Let’s take that discussion a step further.

The S&P 500 (SPX) trades at about 21 times forward earnings. That’s the 87th percentile of valuations since 1980. On any traditional screen it looks extreme. Especially when you consider the 30% growth in earnings required to hit that.

AI infrastructure alone accounts for roughly half the earnings growth in the market this year.

With the boom in AI infrastructure, high energy prices, and a weak USD, this level of growth is well within the realm of achievable.

And beatable even.

That’s the possibility the bears keep skipping. The most expensive market in four decades might appear cheap in hindsight.

Here’s why that matters to the yen.

An economy that grows into a valuation like that is likely to see inflation and rate hikes.

The AI build-out alone adds interest rate pressure through three mechanisms.

The first is debt. Hyperscalers are on track to issue roughly US$400 billion in debt for 2026. AI-related paper now makes up close to 30% of net new investment-grade supply in the US dollar market.

Every one of those bonds competes with a Treasury for the same pool of savings.

The second is power. Household electricity prices in the US rose 10% over two years. Sure, the Middle East conflict has lit a fire under energy, but it’s not the only factor. Data centre demand adds an estimated 0.1 percentage points to core Personal Consumption Expenditures (PCE) inflation in 2026 and again in 2027.

The third is the absence of a recession. A trillion-dollar capital spending programme doesn’t leave room for the slowdown that usually delivers rate cuts.

Add it up and the market now prices a ~40% chance the Fed hikes in September.

So consider what Tokyo is up against.

Japan is trying to buy a currency whose weakness is caused by an interest rate gap, while the other side of that gap is being widened by the largest capital investment boom in modern history.

The AI boom is steamrolling the yen.

Why Japan Can’t Just Raise Rates

Every analyst has the same fix for the yen. Raise rates properly and the currency takes care of itself.

Look at what that costs.

Japan’s government debt hit ¥1.34 quadrillion. No, I’m not making up words. A quadrillion is a thousand-trillion. Or a million-billion to put it another way.

That’s roughly US$8.4 trillion. The national budget for fiscal year 2026 is US$767 billion. Debt servicing jumped to US$196 billion.

More than a quarter of the national budget now goes to interest and redemption.

Worse, that number is built on an assumed interest rate of 3.0%, the highest assumption in 29 years. The 10-year Japanese Government Bond (JGB) yield is 2.81% and has been climbing since it broke 2% in December for the first time in two decades. The 30-year touched 3.89% in January.

Then there’s the politics.

Prime Minister Sanae Takaichi won a two-thirds majority on 8 February and governs as an expansionist. Her ¥21.3 trillion stimulus package is the largest in years. Cost-of-living support, a fuel tax cut, ¥7.2 trillion for strategic investment in AI, semiconductors and quantum.

Markets nicknamed it the Takaichi Trade.

Japan’s fiscal policy is designed to push money out the door, which pushes the yen down, and the same government then spends US$53 billion of reserves buying that yen back.

One hand pours. The other bails.

The Five Thousand Dollar House Problem

There’s a deeper reason Japan can’t grow its way out, and you can see it from a train window.

Japan has about nine million empty houses. Akiya. That’s 13.8% of the entire national housing stock, and roughly 3.85 million of them are long-term abandoned, neither for sale nor rented nor used.

Country towns give them away. Some are listed at ¥1. Habitable rural homes trade between the equivalent of about A$5,000 and A$50,000, and municipalities will pay you to renovate them because they’d rather have a neighbour than a ruin.

A house for less than a second-hand car.

The numbers behind it are bleak. Japan recorded 705,809 births in 2025, the tenth straight annual fall. The fertility rate is 1.15. The population is down to 122.86 million and shrinking by roughly 580,000 people a year.

Takaichi calls it ‘a quiet state of emergency’.

There are two ways out of a shrinking workforce. Have more children, or import them.

The first takes twenty years to show up in a tax base. The second is politically closed. Under pressure from the ‘Japanese first’ Sanseito party, Takaichi has committed to tougher immigration rules, and she needs those votes.

So Japan is locked in from every side.

It can’t raise rates hard, because the budget is already a quarter debt service. It can’t grow its way out, because the workforce shrinks every year. It won’t import workers, because the coalition maths forbids it. And it keeps running fiscal deficits that push the currency lower.

When a country closes off every adjustment valve, the pressure comes out of the one thing left that can still move freely.

The exchange rate.

That’s why the yen keeps falling. And it’s why intervention is treating a symptom while the disease is fully funded and running.

This is an illness that a bandaid can’t fix.

Where This Actually Breaks

Now the part that reaches your portfolio.

For thirty years, the yen has been the world’s funding currency. Borrow at near zero in Tokyo. Buy something that yields more anywhere else. Keep the difference, and enjoy a falling yen making the loan cheaper to repay.

The carry trade.

Australia has been one of the favourite destinations. Our cash rate is 4.35% against Japan’s 1.00%, and the Australian dollar touched 114.75 yen on 2 June, a 35-year high.

Treat that pair as a leverage gauge for the whole system.

We laid out the mechanism in The Yen Carry Trade Unwind, and you’ve already seen the live demonstration.

On 5 August 2024, the Bank of Japan hiked, the yen surged, and the trade went into reverse. The Nikkei 225 (NI225) fell 12.4% in a day, its largest points loss on record. The CBOE Volatility Index (CBOE:VIX) touched 65. The S&P/ASX 200 (ASX:XJO) dropped 3.7% for reasons that had nothing to do with Australia.

That was just a warning shot.

If inflation in Japan really starts to take off, hikes could come thicker and faster than anyone expects.

That could mean a violent and disorderly unwind.

This is the kind of loaded gun that can ruin hedge funds and cause a global recession. It has the potential to be a major shakeup, and it’s worth having on the radar.

The Edge

Three markers to watch, and dates for them.

The first is 160 on the US dollar/yen pair (USD/JPY). That’s the line Tokyo has defended twice. A clean break with no response tells you the authorities have run out of appetite, and the market will test how far it can push.

The second is 17 August.

US Treasury International Capital (TIC) data for June lands at 4pm Washington time, and it updates Japan’s Treasury holdings from the US$1.14 trillion figure we have for May. Another sharp fall would say Tokyo is drawing down harder than it’s admitting. Watch it alongside the Ministry of Finance’s monthly intervention disclosure at the end of August, which confirms exactly what was spent.

The third is September, when the Bank of Japan and the Federal Reserve meet within weeks of each other. A BOJ hike could see a big reaction. If that’s quickly followed by a Fed hold, the market may start to extrapolate those two paths.

For your own portfolio, the practical read is simple.

US and ASX stocks and bonds are susceptible to unexpected Japanese interest rate hikes. The carry trade is crowded, and any unwind could be messy.

We’d expect serious government and central bank intervention from multiple countries if this unwind really starts. If left unchecked, such an unwind could be catastrophic for the markets.

If you own Australian banks, miners, or anything that moves with global risk appetite, you’re exposed to a yen rally whether you chose it or not.

Two governments put US$60 billion on the table and bought twelve days.

The gap that beat them is still open, held there by a data centre boom on one side and a pension crisis on the other. Neither of those resolves this year.

Watch 160 in the US dollar/yen pair. Then watch Japanese inflation, and the Bank of Japan decisions that follow it.