The yen's recent recovery from four-decade lows, supported by a rare joint intervention with the United States, is now at risk of fading. Market bets on faster and more aggressive interest rate hikes by the Bank of Japan (BOJ) have surged, as the currency's stability hinges on the central bank's policy meeting next month.

In late July and early August, coordinated intervention by Japan, the U.S. Treasury, and South Korea propelled the yen up by about 5% from its 40-year trough of 163.99 against the U.S. dollar. However, the rally failed to hold, with the yen weakening back above 159, having briefly touched a high of 155.20. More significant than the exchange rate moves is the sharp repricing of interest rate expectations. Markets perceive that the U.S. is pressuring Japan to back its intervention with policy action, leading traders to price in an additional 25 basis points of rate hikes for the year. Data from Tokyo Tanshi shows the probability of a September rate hike has jumped to 76%, up from just 24% on July 30.

“We need to see a more hawkish stance from the BOJ, and the market is trying to price that in, but at the same time, we need the central bank to validate it,” said Moh Siong Sim, a foreign exchange strategist at OCBC in Singapore. “If the bank fails to deliver, the yen will weaken again.” This puts the BOJ under immense pressure: either deliver on the hawkish expectations already priced in or risk watching the yen slide back to multi-decade lows.

Government Shift in Stance, Bessent's Pressure Pays Off

According to sources, the government of Prime Minister Shigeru Ishiba now supports a near-term BOJ rate hike, with a possible window in September or October. The BOJ's concern that yen weakness is pushing up prices aligns with the government's goal of solidifying the recent joint U.S.-Japan intervention's effects. While the BOJ has legal independence on monetary policy, the cabinet can influence decisions through signaling. The Prime Minister's office stated in an email, “We believe that specific monetary policy measures, including interest rate hikes, should be decided by the BOJ,” adding that the central bank should work closely with the government to achieve the 2% inflation target in a “stable manner.” The BOJ declined to comment.

U.S. Treasury Secretary Scott Bessent has been a key trigger for this repricing. He publicly urged Japan to follow the joint intervention with “policy and fundamentals,” a move widely interpreted as pressuring the Ishiba administration to soften its dovish stance and allow the BOJ to raise rates. “With political pressure easing, the BOJ is likely to accelerate the pace of rate hikes,” said Takahide Kiuchi, an executive economist at Nomura Research Institute.

Ishiba had previously been seen as cautious about rapid rate hikes, fearing it could stifle the economic recovery. Since taking office in October last year, the BOJ has raised rates twice, but the benchmark rate remains at just 1%. A further increase in September or October would mark the fastest tightening cycle in 12 months since the asset bubble peak in 1989.

Joint Intervention and FIMA 'Bazooka' Backstop

The yen's long-term depreciation is rooted in the widening U.S.-Japan interest rate differential, which accelerated this year due to Ishiba's large-scale stimulus and the BOJ's delayed rate hikes. Record unilateral intervention by Japan in April and May failed to reverse the trend, and it took a joint dollar-buying operation with the U.S. Treasury to pull the yen back from its 40-year low. Japan's Finance Ministry has pledged to act again without hesitation after the July 30-31 joint intervention with the U.S. Treasury, the first such coordinated action since 1998.

This intervention introduced a new financing arrangement. Japan can borrow dollars through the Federal Reserve's FIMA repo facility, using its holdings of U.S. Treasuries as collateral, without having to directly sell the bonds to fund intervention. “FIMA is more of a deterrent than a financing tool,” said Masahiko Loo, a senior fixed income strategist at State Street Global Advisors. “It's a 'bazooka-like' backstop that forces the market to think twice before challenging policymakers' resolve.”

Rate Hikes Become 'Only Cure,' BOJ Faces Validation Moment

Beyond intervention, the BOJ has become the key variable for the yen's sustained stability. Katsutoshi Inadome, a senior strategist at Sumitomo Mitsui Trust Asset Management, stated bluntly, “In the short term, the only cure for yen weakness is a BOJ rate hike.” Mizuho Securities has moved its base case for the next rate hike to September, citing the unexpectedly hawkish tone of the BOJ's July summary of opinions, and has raised its terminal rate forecast from 1.50% to 1.75%.

Internal signals from the central bank are also reinforcing this expectation. BOJ Governor Kazuo Ueda, after keeping rates unchanged on July 31, hinted at a faster pace of rate hikes due to upside risks to prices, and later that day, the U.S. and Japan coordinated their intervention. Sources say the government conveyed support for Ueda's hawkish comments at a press conference ahead of the July meeting. The BOJ's July summary of opinions showed one member saying that, given the underlying CPI inflation is near 2%, “the pace of policy rate hikes could be faster than market expectations,” while another member argued for greater flexibility in monetary policy. BOJ officials are reportedly still assessing economic and price developments before deciding on the timing of a rate hike, but have not ruled out action in September.

Despite the temporary support from intervention and rate hike expectations, the yen still faces structural headwinds. Strategists at Mitsubishi UFJ Morgan Stanley Securities point to ongoing concerns about Japan's fiscal deficit and unfunded tax cuts, which could put upward pressure on bond yields and undermine the durability of the intervention. This shifts the focus back to the BOJ. Rinto Maruyama, a senior strategist at SMBC Nikko Securities, warned that bond yields and swap rates have already priced in a September action. If the central bank delays again, it would be interpreted by the market as a “betrayal.” Maruyama added, “Market participants will lose confidence in the BOJ's ability to continue raising rates. In that scenario, the yen will fall, and long-term bond yields will also rise due to heightened inflation concerns.”