The yen intervention on July 30 deserves scrutiny. On the surface, it was about stemming continued yen depreciation, with the U.S. joining forces with Japanese authorities to help prevent an Asian-crisis type currency depreciation spiral. But digging deeper, the story appears to be about growing anxiety about rising U.S. Treasury yields and the risks of uncoordinated policy in an environment of growing financial vulnerabilities.

Drivers of yen weakness

Yen weakness is driven by fundamentals and macroeconomic policies. The Bank of Japan (BOJ) is moving in the right direction. It has successfully allowed its economy to reflate after decades of entrenched disinflationary expectations. But the pace of tightening is too timid. Monetary policy remains accommodative, with short-term real rates still negative. Meanwhile, the fiscal position is improving, but the Takaichi government is considering tax cuts, with the prospect of expansionary fiscal policy compounding the yen depreciation. The weak yen is becoming a political liability amid widespread household discontent about inflationary pressures.

This helps explain the dramatic steepening of the Japanese government bond (JGB) yield curve, with 10-year yields at 2.8% and 30-year yields near 4%. The BOJ’s quantitative tightening has likely played a role by signaling an end of attempts to manage the 10y JGB yield, but it appears to be modest. BOJ holdings have fallen from nearly 55% to just below 50% of JGBs outstanding.

Against this backdrop, it is not clear how temporary intervention to support the yen can have sustained effects without a directional change in policy. The yen traded in a band of 160-164 against USD from early July until the intervention. Rather than FX volatility or distress conditions, this was about the level of the USD/yen pair, with FX intervention trying to lean against market-driven fundamentals. Market estimates suggest Japanese authorities spent about $53 billion, plus reportedly another $5 to $10 billion by the U.S. Treasury.

FX interventions without fundamental policy changes and broad international coordination (like G7) rarely generate sustained effects. Markets test the resolve of policymakers, and the yen has already recovered about 50% of the appreciation since July 30, closing almost at 160 on August 12. Unless the BOJ tightens aggressively or Japan’s fiscal position improves materially, further weakness is likely.

The risk of upward pressure on U.S. Treasury yields

Here is where the narrative unravels. U.S. Treasury Secretary Scott Bessent framed the American intervention as supporting a geopolitical ally and preventing a repeat of the 1997 Asian crisis, with a risk of competitive devaluations across Asia. That rationale is misleading. The real concern was the U.S. Treasury market.

After the July Federal Open Market Committee (FOMC) press conference, 30-year Treasury yields surged to nearly 5.3%—the highest level since 2007. The trigger was reportedly investors’ sudden concerns about Chairman Kevin Warsh’s commitment to price stability, amplified by rising anxiety among bond investors about the U.S. unsustainable fiscal outlook. Costs of servicing U.S. public debt are rising and elevated borrowing costs by U.S. households and firms are becoming a liability heading into mid-term elections. In this environment, Japanese authorities selling Treasury securities to support the yen would have put additional upward pressure on U.S. yields.

The U.S. coordinated intervention was designed to prevent exactly that. By selling euros to buy yen, the U.S. Treasury signaled support for Japan while lessening the need for a forced Japanese sale of U.S. Treasuries. Yet this reveals the real apprehension about rising yields in the U.S. Treasury market, not about financial stability in Asia.

There is a variety of estimates from academic papers about the impact on Treasury yields of FX intervention through sales of U.S. Treasuries, ranging from 20 basis points to 100 basis points per one standard deviation of sales. For example, recent work by Ahmed and Rebucci focusing on foreign central bank sales estimates the impact to be 30 basis points to 60 basis points. Obviously, the impact depends on a number of factors, including stress conditions in FX markets and underlying dynamics in the U.S. Treasury market, which tend to amplify the effect.

The U.S. FX intervention

The form of U.S. intervention is equally concerning. The U.S. Treasury acted unilaterally, selling euros not only without coordination with the G7 but without pre-emptively informing the ECB, which was apparently blindsided by it. This breakdown of coordination among fiscal authorities and central banks comes at a dangerous moment, given rising risks to financial stability from stretched asset valuations, growing use of financial leverage, concerns about private credit, and the global macro bet on AI. The international collaboration under former Fed Chair Jerome Powell that had resisted the financial fragmentation stemming from geopolitical tensions is showing signs of strain.

Looking ahead, if the BOJ tightens aggressively to fight yen weakness, the interest-rate differential with the U.S. will narrow at the front end (at the long end it has already compressed). This will have two implications. First, carry trades, where investors fund in yen to invest in higher-yielding assets abroad, could become less profitable. Second, Japanese investors, who hold a significant share of U.S. fixed-income assets (including U.S. Treasuries and corporate bonds), may repatriate funds as Japanese yields become more attractive. The combination of rapidly unwinding carry trades, as seen in August 2024, and capital repatriation would likely put significant upward pressure on U.S. rates, the opposite of what U.S. policymakers want to see.

The role of FIMA

Treasury Secretary Bessent has suggested that, to prevent such outcome, Japanese authorities may use the Fed’s Foreign and International Monetary Authorities (FIMA) Repo Facility. In fact, the Japanese Ministry of Finance (MOF) has indicated on August 3 that it plans to use FIMA in the future.

“On Friday 31st, July (U.S. Eastern Time), Japan’s Ministry of Finance purchased the Japanese yen in coordination with the U.S. Department of the Treasury. This joint action was taken pursuant to the U.S.-Japan Finance Ministers’ Joint Statement issued in September 2025 and countered excessive volatility and disorderly movements in the Japanese yen in recent months. The Japanese Ministry of Finance remains attentive and in close communication with our counterparts at the U.S. Treasury. We will not hesitate to conduct further joint intervention. Japan also plans to utilize the Federal Reserve’s Foreign and International Monetary Authorities (FIMA) Repo Facility in the future.”

This suggestion is troubling. FIMA was introduced in March 2020 to support market functioning and reduce the risk of sharp yield spikes during market stress.

“The Federal Reserve established a repurchase agreement facility for foreign and international monetary authorities (FIMA Repo Facility). By creating a backstop source of temporary dollar liquidity for FIMA account holders, the facility can help address pressures in global dollar funding markets that could otherwise affect financial market conditions in the United States. Its role as a liquidity backstop also helps to support the smooth functioning of financial markets more generally.”

It was never intended to support the U.S. Treasury FX intervention. Expanding it for that purpose sets a dangerous precedent: using Fed facilities to address fiscal concerns, which would erode Fed independence.

Also, why would Japanese authorities use FIMA? The MOF reports to have cash on hand representing about 15% of its FX holdings (although the currency composition is not known and such source of liquidity seems to be rarely used for FX intervention). Some market participants have also noted that the Japanese authorities may have USD parked at the Federal Reserve Bank of New York’s Foreign Official Reverse Repo Pool, where foreign central banks temporarily lend U.S. dollars to the Fed in exchange for U.S. Treasury securities. There are currently about $317 billion in that facility (as of August 5), but the counterparties are not publicly available.

Moreover, FIMA is also more costly than funding repo in private markets. According to FOMC rules and authorizations:

“The repurchase agreement transactions hereby directed shall (i) include only U.S. Treasury securities; (ii) be conducted with Foreign Accounts approved in advance by the Foreign Currency Subcommittee (the “Subcommittee”); (iii) be conducted at the rate for Standing Overnight Repurchase Agreement Operations for an overnight term, or at a rate equal to the rate on overnight index swaps of a weekly maturity plus 25 basis points for a seven day term, unless the Subcommittee establishes a different rate; (iv) be offered on an overnight basis or a term of seven calendar days; and (v) be subject to a total outstanding per-counterparty limit of $60 billion at any given time.”

At its July meeting, the FOMC directed the Desk to conduct standing overnight repurchase agreement operations at a rate of 3.75 percent. But Secured Overnight Financing Rate (SOFR) is currently 3.63%. And term repo would be even costlier given the 25 basis point add-on. Japanese authorities may find it in their interest to borrow at a small spread than sell Treasuries into a market with falling prices, but the fact that FIMA was invoked suggests real concern about the risk of stress in the U.S. Treasury market.

Treasury Secretary Bessent has suggested that the Fed raise the FIMA counterparty cap beyond $60 billion, framing the FIMA Repo Facility as no different than an FX swap line. This has troubling governance implications. According to FOMC rules and authorizations, the FX Subcommittee (chaired by the Fed Chairman with the New York Fed President and the Federal Reserve Board Vice-Chair for monetary policy) can approve changes to FIMA terms. Will the FOMC go along with it? How will Fed credibility be affected if there is dissent, especially given the opaque nature of this facility?

“The Subcommittee may approve changes in the rate, the maturity of the transactions, eligible Foreign Accounts counterparties (either by approving or removing account access), and the counter-party limit; and the Subcommittee shall keep the Committee informed of any such changes. The Desk will also report at least annually to the Committee on operations directed in this paragraph and on the list of approved account holders.”

The optics of fiscal dominance

If the U.S. Treasury successfully pushes for expanded FIMA use, the optics of fiscal dominance become hard to ignore, with the Fed balance sheet deployed to mitigate rising U.S. interest rates and an unsustainable fiscal outlook. Central bank credibility depends on independence from political pressure. This is particularly relevant now given that inflation has been above target for years and investors are testing the Fed’s resolve.

The July yen intervention ultimately reveals a U.S. Treasury anxious about rising yields, and willing to blur lines between currency intervention, debt management, and monetary policy in the process. For investors, the lesson is clear: international coordination is breaking down, and the tools being deployed are increasingly blunt and politically motivated. That is a recipe for continued volatility and higher yields.

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