Fiat Elpis · FX and monetary policy note 18
Long USD/JPY: the Fed follows through, the BoJ faces a higher bar
The US has the larger inflation problem. December remains live for the Fed. The BoJ has more room to temper expectations for what comes next.
Fiat Elpis macro research · After the Fed decision, ahead of the 18 September BoJ decision
My new trade idea is long USD/JPY. I expect US inflation to keep the Fed committed to further restraint, while Japan's more contained current inflation gives the BoJ room to deliver a hike without endorsing an aggressive sequence. Recent flows toward the yen make that difference in follow-through more consequential.
01 · The long-USD/JPY thesis
Warsh leaves the next hike on the table
The Fed raised its target range to 3.75–4.00% on September 16. The new projections point to another increase this year and a hold through 2027. My read is that Warsh has left investors room to retain a December hike in the curve: the first move does not close the inflation debate.1
The quarter-point hike was expected, and December tightening was already substantially priced. The case for long USD/JPY rests on what happens next: the US path holds firm or rises, while the Japanese path loses some of its anticipated speed. Pre-decision pricing placed December US rates near 4.14% and Japan's June 2027 overnight rate near 1.77%. Both curves already demanded follow-through.2
This is a firmer reading of US policy than the dovish-hike scenario in my 15 September note. The outcome leaves further tightening intact. For this FX trade, I expect the Fed to deliver more sustained restraint than the dovish narrative allows, while the BoJ moderates expectations beyond its next move.
“The Fed has more reason to sustain tightening. The BoJ has more room to disappoint expectations for the pace.”
Fiat Elpis USD/JPY thesis, 16 September 2026
02 · The inflation and policy gap
The inflation gap gives the two banks different room to act
A larger overshoot to bring back under control
July PCE inflation was 3.7% year on year, with core PCE at 3.3%. August headline CPI was 3.4%. The Fed has a substantial distance to travel to its 2% PCE objective. Energy and freight can also feed into core prices, so this is a judgment about the persistence of the pressure, not a claim that all of it comes from domestic demand.34
Current inflation is much closer to target
July national CPI was 1.9%; excluding fresh food it was 1.8%, and excluding fresh food and energy it was 1.9%. On September 10, a BoJ board member described underlying inflation as still below 2%, though very close. That gives the bank more scope to be measured about the pace.56
A hike alone may not satisfy yen bulls
The decision is due Friday, September 18. A move from 1.00% to 1.25% is the consensus expectation in the pre-meeting survey. The June 2027 pricing near 1.77% implies roughly two further quarter-point moves beyond that expected hike. My forecast is that Ueda delivers the expected move but tempers confidence in rapid follow-ups.27
The trade
Long USD/JPY on firmer US follow-through and a slower Japanese path than the market anticipates. The catalyst is a change in the expected interest-rate differential. A familiar rate advantage alone is already in the price.03 · Positioning and expectations
The recent positioning shift raises the cost of a BoJ disappointment
The broad speculative yen futures measure was net long 10,796 contracts on September 8. Leveraged funds were still net short 49,098, but that short had fallen from 102,188 a week earlier. These are different reporting groups, with the same useful message about recent direction: substantial yen short-covering has already taken place.89
Reported options demand has also favored yen upside. I read this as a market increasingly prepared for a stronger yen, although positioning is not uniform. If Ueda fails to validate the anticipated pace, that recent shift can reverse. The long-dollar catalyst would be a softer Japanese rate path meeting continued US restraint.10
Japan still has reasons to tighten. Its low current CPI partly reflects government measures, and the BoJ forecasts inflation above 2% further ahead. My disagreement is about speed: those risks do not require Ueda to endorse the full sequence investors are anticipating at this meeting.611
- US follow-through: December tightening remains credible as incoming inflation sustains the case for restraint.
- Japanese restraint on guidance: the BoJ delivers its expected hike without validating an accelerated sequence.
- The FX transmission: expected US–Japan short-rate spreads widen relative to the current curve, supporting USD/JPY.
- The positioning response: disappointment with the Japanese path interrupts the recent shift toward yen strength.
04 · What would invalidate the long
What would invalidate the long
The trade needs the relative policy path to move in the dollar's favor.
- A more hawkish BoJ: an outsized hike or convincing support for rapid successive increases pushes the Japanese curve higher.
- A softer US path: convincing disinflation or weaker activity removes the case for December tightening and compresses the expected rate spread.
- Yen demand overwhelms the spread: intervention or a sharp carry unwind produces sustained yen appreciation despite the policy gap.
The USD/JPY call
The asymmetry favors the dollar
My call is long USD/JPY. The Fed faces the larger current inflation overshoot and has kept further tightening in play. The BoJ faces a market that already expects repeated hikes, with more contained current inflation giving it room to proceed carefully.
I expect the Fed to overdeliver through persistence and the BoJ to temper the pace. That is the policy divergence I want to express, with the recent shift toward yen strength adding sensitivity to a Japanese disappointment.
Sources & method
Sources and context
- 1. Reuters, September 16, 2026 — Fed raises rates to 3.75–4.00%; projections show another increase this year and a hold in 2027.
- 2. Bloomberg market context supplied by the author, September 16 — pre-FOMC US futures and Japan OIS snapshots; September 10 BoJ survey. The linked survey supports the expected BoJ hike; curve levels are from the supplied terminal queries.
- 3. US Bureau of Economic Analysis — July 2026 Personal Income and Outlays, released August 26: PCE 3.7%, core PCE 3.3% year on year.
- 4. US Bureau of Labor Statistics — August 2026 CPI, released September 11: headline 3.4% year on year.
- 5. Statistics Bureau of Japan — July 2026 national CPI, 2025 base, released August 21. Japan's exclusion measures differ from US core PCE and core CPI.
- 6. BoJ board member Kazuyuki Masu — September 10, 2026 speech: underlying inflation near but below 2%, policy effects on measured CPI, and reasons for further normalization.
- 7. Bank of Japan — official calendar: monetary-policy meeting September 17–18, 2026.
- 8. CFTC — legacy futures-only report, Japanese yen, positions September 8, released September 11: noncommercial longs 178,791 less shorts 167,995.
- 9. CFTC — Traders in Financial Futures, futures only, positions September 8: leveraged-fund longs 81,760 less shorts 130,858; weekly net shift +53,090.
- 10. Bloomberg, September 11, 2026 — Long-Term Yen-Bullish Options in Demand Even as Spot Retreats; supplied source context.
- 11. Bank of Japan — July 2026 Outlook Report: projected inflation above 2% and upside price risks.
Written on 16 September 2026 after the Fed decision and before the BoJ decision. The long USD/JPY call and expected relative policy paths are the author's thesis. December is a potential meeting for further Fed tightening, not a committee commitment. Market-curve figures are the supplied pre-FOMC September 16 snapshot, not post-decision readings. US and Japanese inflation measures retain their own baskets and reference months. CFTC figures refer to September 8; linked reports roll forward over time. No executed entry, position size, stop or price target is asserted.