Newsletter · · Ashutosh Agarwal

The Yen Line in the Sand at 155 - G10 FX Weekly - Week of September 7, 2026

G10 FX Weekly for the week of September 7, 2026. Podcast synthesis on why 155 yen to the dollar became the most-watched level in currency markets, the J.P. Morgan estimate that over 100 billion dollars of dollar-yen may need to unwind below it, Japan's 217 billion dollar pension-fund wildcard, a second European Central Bank hike driven by the oil shock, and the gilt selloff that split the desks.

G10 FX Weekly

Week of September 7, 2026: The Yen Line in the Sand at 155

Last week this newsletter was about the Swiss franc, the funding currency everyone had quietly crowded into. This week the spotlight swung hard to the other funder, the Japanese yen, and to one very specific number that has become the most-watched level in all of currency markets: 155 yen to the dollar.

But step back first, because there's a bigger story underneath, and it explains almost everything that moved this week. A shooting war between the United States and Iran has flared back up, with tankers attacked in the Gulf and oil spiking, and that oil shock is doing something we haven't seen in years: it is turning the world's central banks into hawks all at once. Europe is about to raise interest rates for the second time. Australia has hiked three times this year. New Zealand just hiked. Japan is expected to hike within days. Even the US Federal Reserve, which markets spent all of 2025 expecting to cut, is now priced to possibly raise rates.

When everyone tightens together, government bonds sell off together, and this week they did, violently, from Washington to London to Tokyo. That is the current running under every currency story below.

Quick definition, because it comes up constantly. A carry trade is the simplest idea in finance: borrow a currency that pays almost no interest (the "funding currency"), use the cash to buy a currency or asset that pays a lot, and pocket the difference. For decades the favourite thing to borrow has been the yen, because Japan's interest rates sat near zero. The catch: when too many people borrow the same currency and it suddenly jumps in value, they all rush to buy it back at once to repay their loans, and that stampede is what makes a carry-trade unwind so violent. That is exactly the risk sitting at 155 right now.

TL;DR

  • 155 is the trapdoor. J.P. Morgan's desk (relayed via Bloomberg) reckons roughly ¥15–17 trillion, over $100 billion, of dollar-yen positions may need to unwind if the pair trades below 155, potentially cascading the rate down to 142–146 (Saxo Market Call, Sep 4). It dipped to about 155.30 this week and bounced.
  • The Bank of Japan is finally the story, not the sideshow. Markets now fully price a September rate hike and about 75 basis points of Japanese tightening through next April; one board member wouldn't rule out a jumbo 50bp move (At Any Rate, Sep 4). (A basis point is one-hundredth of a percentage point.)
  • Japan's giant pension fund could add fuel. J.P. Morgan flags that GPIF, the world's largest pension fund, held an unusual August meeting and could shift up to ¥33.8 trillion (~$217bn) home, bigger than all of this year's official intervention combined (At Any Rate, Sep 4).
  • Europe hikes again, and isn't done. A 25bp ECB hike on Thursday is "a done deal," a December hike is now penciled in, and a third is "more and more likely," says J.P. Morgan's economics team, all driven by the oil-fed inflation (Global Data Pod, Sep 4).
  • The clean euro bull: Steno Research's Andreas Steno Larsen says "the European Central Bank will out-hawk the Fed," pushing EUR/USD higher, a trade he's "been incredibly right on… since early July" (Real Vision Macro Mondays, Aug 31).
  • Sterling had an ugly week, with 10-year gilt yields spiking 16bp to 5.22%, the highest since 2008 (NAB Morning Call, Sep 1), but J.P. Morgan argues this is a global bond move, not a UK crisis (At Any Rate, Sep 4).
  • Carry is still winning, and the pros' highest-conviction view is now the carry trade itself, "rather than the dollar." The live debate is which currencies you borrow if the yen becomes unsafe.
  • Politics is back on the euro's radar: a German far-right surge in Sunday's state election and French election drama, including chatter that ECB chief Lagarde could quit to run for president (The KE Report, Sep 4).

What's new

1. The number that matters: 155

If you remember one level from this newsletter, make it this one. 155 yen per dollar is where the whole carry world could tip over.

Here's why, in plain terms. For years, traders have borrowed cheap yen and bought higher-yielding things elsewhere. To do that they had to sell yen, which is part of what kept the yen weak (it recently touched a 40-year low). If the yen suddenly strengthens through a key level, those traders get squeezed: they have to buy yen back fast to cover, which pushes the yen up further, which squeezes the next person, and so on.

On Saxo Market Call (Sep 4), Saxo's John Hardy laid out the mechanics, citing a J.P. Morgan estimate relayed by Bloomberg:

JP Morgan is saying that there could be some… around 100+ billion US dollars in dollar-yen that could sort of be stuck in a need to unwind should we start trading below 155. There could be a cascade of position squaring that could drive dollar-yen… to the 142 to 146 range.

That is a potential 6–8% collapse in the dollar against the yen if one line breaks. Hardy notes 155 is "a massive area… head and shoulders" on the charts (a classic reversal pattern), and this week the pair got down to the "low 155s" before bouncing.

Why it matters: a move from 155 to 145 wouldn't stay in Japan. Because the yen funds so many other bets, a sharp yen rally forces selling of everything the borrowed money bought: US stocks, bonds, emerging-market currencies. This is the single most important trip-wire in global markets right now, and it's just a few big figures away.

2. The Bank of Japan is done being passive, and the US is leaning on it

The reason 155 is suddenly in play is that the Bank of Japan looks genuinely ready to raise rates faster than anyone expected. On J.P. Morgan's flagship At Any Rate FX podcast (Sep 4), co-head of FX strategy Meera Chandan and the team walked through what changed.

Markets now fully price a September hike, and Japan's one-year interest-rate expectations have jumped to around 2%. A board member, Takada, went further on September 2 and wouldn't rule out either a jumbo half-point hike or back-to-back hikes, though J.P. Morgan thinks consecutive quarter-point moves are the likelier path. Their economists see Japanese rates reaching 2% by the middle of next year and 2.25% by year-end. For a country that spent 30 years near zero, that is a regime change.

There's a geopolitical twist too. US Treasury Secretary Scott Bessent has, unusually, been pushing Japan to strengthen its currency, even helping intervene directly. As Chandan put it, Bessent has been "passing the baton on to Japanese authorities," which nudged the famously yen-bearish J.P. Morgan desk to turn tactically bullish on the yen "for a very narrow window."

On The KE Report (Sep 4), Bannockburn's Marc Chandler captured the strangeness of Washington's stance: US inflation is higher than Japan's, US growth is stronger, yet the administration wants Japan to hike while the Fed sits still. In his words, "I just don't get where that comes from."

3. Japan's $217 billion wildcard: the world's biggest pension fund

Here's the fresh piece of news that could turbo-charge a yen move. Japan's Government Pension Investment Fund (GPIF), the largest pension fund on the planet, rivalling Norway's oil fund, did something odd: it held a management-committee meeting in August, the first August meeting in seven years, and put its asset allocation back on the agenda just five months after deciding no change was needed.

Why should anyone outside Tokyo care? Because if GPIF simply shifts its money to the top of its existing allowed ranges, buying more Japanese bonds and stocks, and therefore bringing money home, J.P. Morgan estimates that implies roughly ¥33.8 trillion, about $217 billion, of yen buying and foreign-currency selling. To put that in perspective, that is about a quarter larger than all of Japan's official currency intervention so far this year (¥27.2 trillion, ~$174bn).

The first hard clue arrives with Japan's monthly flow data on September 8. Saxo's John Hardy framed the stakes on Saxo Market Call: GPIF's allocation to Japanese government bonds has fallen from over 60% before 2013 to around 25% today. Even a partial reversal would be an enormous flow, and it would push the yen the same direction as the rate hikes.

4. Europe is about to hike for the second time, and that's the euro's quiet bull case

While Japan grabbed the headlines, the European Central Bank quietly did something remarkable: it's raising rates again, into what everyone assumed was the end of the hiking cycle. On J.P. Morgan's Global Data Pod (Sep 4), economist Raphael upgraded his own forecast on air:

September has been, you know… that's basically a done deal already… the longer the whole situation in the Middle East rumbles on… time is running out for there to be a proper de-escalation… So I put that [December hike] forecast in.

His logic is the oil shock. With Brent oil assumed around $90 and European natural gas staying elevated, headline inflation runs near 3.5% into early next year and core inflation is "stuck at two and a half until next spring." He now sees a September hike, a December hike, and a third "more and more likely," with a possible fourth in March 2027. J.P. Morgan's rates strategist Khagendra Gupta thinks the market's pricing of about 75bp of hikes is only "maybe 10 basis points too high," and pointedly, he's "not fading these moves given the uncertainty around Middle East."

The sharpest version of the euro-bull trade came from Real Vision's Macro Mondays (Aug 31), where Steno Research's Andreas Steno Larsen made the case directly:

as long as we have this products inflation in the oil space… it is a good working assumption that the European Central Bank will out-hawk the Fed. And that kind of supports the notion that the Euro versus the dollar goes up. We've been incredibly right on that trade since early July.

The euro sits a shade below 1.16 to the dollar. The bull argument is simple: if Europe is hiking harder than the US, money flows toward the higher, rising yield.

5. Sterling's ugly week, crisis or just caught in the crossfire?

British government bonds had a rough few days, and it produced the newsletter's best genuine disagreement. On NAB Morning Call (Sep 1), NAB's Ray Attrill reported UK 10-year gilt yields jumping 16 basis points overnight to 5.22%, the highest since 2008, and revived an old phrase:

the term… bond market vigilantes… coined by that veteran Wall Street economist… Ed Yardeni back in 1983… if the fiscal and monetary authorities won't regulate the economy, then bond investors will.

"Bond vigilantes" are simply investors who dump a government's bonds to protest deficits and inflation, forcing borrowing costs up. Attrill's worry is that this time oil is rising (in the 1980s episode it was falling), compounding both inflation and fiscal fears, and Britain looks worse-placed than peers, with retail inflation at 3.5%, a new prime minister (Andy Burnham) under pressure to lift defence spending, and a late-October budget looming. As he put it, "The UK, like everyone, is suffering, but they seem to be doing slightly worse."

But J.P. Morgan's Head of European Rate Strategy, Francis Diamond, pushed back hard on At Any Rate (Sep 4), asked directly whether this was a UK-specific problem:

the simple answer is no. I don't really think the recent sell-off in 10-year or 30-year is just UK idiosyncratic factors.

His model shows gilts moving in lockstep with US Treasuries, driven by global forces: higher oil, a more activist US Treasury, hyperscaler bond issuance crowding the market. He notes the sell-off has mechanically cut the government's fiscal "headroom" from about £22 billion at the last budget to roughly £13 billion, but insists the yield move itself "is really not a fiscal story." The real test, he says, comes at the October budget.

Barclays offered the calmer medium-term view. On Tech Disruptors (Sep 3), Barclays' Jack Meaning expects the Bank of England to hold Bank Rate at 3.75% through the end of 2026 and only start cutting in 2027, with inflation peaking around 3.2% this quarter before drifting back toward 2%.

6. The carry trade is still king, but the throne might change hands

Even with all this drama, the carry trade is still making money. J.P. Morgan's At Any Rate (Sep 4) made the striking point that carry has delivered "really strong returns year-to-date, even though the dollar hasn't done much," so much so that "the more higher conviction view is really the carry and the beta positive view of the world rather than the dollar itself."

The interesting question is what you borrow if the yen becomes dangerous. On Bloomberg Surveillance (Sep 3), TD Securities' Jati Badwaj, author of a note wonderfully titled No Country for Strong Yen, argued that if the Bank of Japan signals an aggressive hiking cycle, the yen shorts (at "a three-decade extreme high") will unwind and force "a big carry rotation to different funders and, in fact, even different longs." His candidates to become the new funding currencies: the Canadian dollar (its central bank is least likely to hike) and the Swiss franc. On the buy side, his top pick is the South African rand, "very well commodity diversified… benefits with gold prices," while he'd wait out Brazil's election before buying the real, and calls the Mexican peso "extremely… crowded."

The debate

This week gave us two genuine two-sided fights.

Fight 1: Does a Bank of Japan hike actually rescue the yen?

The bulls (much of the market, plus J.P. Morgan's tactical view) say yes: faster hikes shrink the gap between US and Japanese rates, the crowded yen shorts unwind, and the currency snaps stronger, with 155 as the trigger.

The skeptic is Marc Chandler on The KE Report (Sep 4), and his argument is worth hearing. Japan has already raised rates from below zero to 1% over two years, and the yen fell the whole time, to 40-year lows. He points to a live example from this very week: New Zealand's central bank hiked and signaled more, and the New Zealand dollar still fell about 0.8%, the week's weakest currency. His deeper point, backed by his own correlation work: the dollar-yen exchange rate tracks US interest rates far more closely than Japanese ones. So a 25bp hike, already expected, "isn't going to make that much of a difference." In his telling, traders didn't even exit the carry trade this year, they just "shift[ed] the funding leg from yen to the dollar," which is why the Mexican peso is at multi-year highs even as the yen wobbles.

Fight 2: Is the dollar finally breaking down, or about to bounce?

The dollar-bears had the momentum. Steno Larsen expects a weaker dollar as the ECB out-hawks the Fed and the US Treasury's bond-buying (which he expects to ramp up) adds a second downward shove. TD's Badwaj notes the dollar "finds it easier to sell off than rally," because global investors keep buying US assets but hedging away their dollar exposure.

But J.P. Morgan's own desk refused to abandon its dollar-bull call on At Any Rate (Sep 4), even while admitting frustration. Strategist Pat Locke likened it to last year, when a bullish dollar view "wasn't working from July onwards" and then "came together rather nicely in Q4." His honest tell: with a strong US jobs report (162,000 jobs, unemployment at 4.1%) and a hawkish Fed, sticking with the analysis is the lesser risk, because "trading against your own view is kind of the worst kind of bad decision." Even so, the team conceded the higher-conviction trade is carry, not the dollar itself.

Trades in play

Drawn from what the desks actually said, ranked by usefulness for a book:

  • The marquee trade: long yen, with 155 as the line. The whole complex pivots here. J.P. Morgan is tactically long yen for a narrow window; Saxo's Hardy is "constructive on the yen" and likes euro/yen falling too. The asymmetry is real: a break of 155 could cascade toward 142–146. The risk is that the level holds (as it did in April/May and again in late July) and the yen resumes weakening.
  • Long euro against the dollar. The cleanest expression of "ECB out-hawks the Fed," per Steno Larsen, with an added push if the US Treasury steps up bond-buying. Watch the German election and French politics as the offsetting risks (below).
  • The carry rotation. If you run carry and fear a yen squeeze, TD's Badwaj's playbook is to move your funding toward the Canadian dollar and Swiss franc, and to favour the South African rand on the long side, waiting out Brazil's election and steering clear of the crowded Mexican peso.
  • Fade sterling weakness cautiously. Barclays' hold-then-cut path and J.P. Morgan's "it's global, not a UK crisis" view both argue against panicking on gilts, but nobody wants to be long UK risk into the October budget.

Read-throughs

  • Euro/yen and euro/franc. Saxo's Hardy explicitly likes euro/yen lower; if the yen rallies on a BoJ hike, euro/yen is a cleaner short than dollar/yen because it strips out the dollar's own gyrations. On the franc, note that euro/franc is "now trading at 0.94," per the Market Maker podcast (Sep 4), still below the old 1.20 floor the Swiss abandoned in 2015, and consistent with the franc's enduring strength.
  • Bonds everywhere moved together. UK gilts at 5.22%, US 10-year Treasuries above 4.8% (also the highest since 2008), euro-area 10-year yields around 3.35% (last seen in 2011), and a Japanese 10-year auction clearing above 3% "for the first time since 1996" (NAB, Sep 1). The one twist: Japan's long bonds actually rallied, with 30-year yields dropping below 4% on strong demand (Saxo, Sep 4), a sign the market believes shorter-term hikes will eventually tame inflation.
  • Yen-funded risk assets. As a Bitcoin-focused podcast, Onramp (Aug 31) is a punditry source rather than a trading desk, but its framing is useful color: it cites Deutsche Bank sizing the yen carry trade at roughly $20 trillion with an estimated 0.8 correlation to Bitcoin, and recalls that the August 2024 unwind sent the Nikkei down 12.5% in a day and the Nasdaq down 5%. That is the tail scenario a break of 155 is testing.
  • The intervention playbook, and its limits. The Market Maker hosts (Sep 4) noted Japan has spent a record ¥15.4 trillion (~$96bn) defending the yen, the first joint US-Japan support since 1998, and dryly summarised why it keeps failing: "You can treat the symptom, but unless you cure the disease, it's not going to work." Their warning worth diarising: Japan's "silver week" holiday, September 19–23, thins out trading and is a classic window for a surprise intervention.

What changed

Two weeks ago the funding-currency fear was all about the Swiss franc. This week it moved decisively to the yen, because the yen now has something the franc doesn't: a hard catalyst (a Bank of Japan hike within days), a specific trip-wire (155), and a potential $217 billion pension-fund tailwind behind it. At the same time, the European Central Bank crossed a line of its own, hiking into what everyone had called the end of the cycle, with more to come.

Tying it together is the oil shock from the US-Iran war. It is the reason the ECB keeps hiking, the reason gilts and Treasuries sold off, and the reason the Fed is now priced for possible hikes rather than cuts. The whole G10 has quietly flipped from an easing world to a tightening one, and the most fragile pressure point in that new world is a yen sitting a whisker above 155.

The franc, for its part, has re-entered the conversation in a different role: not as the crowded funder of last issue but as one of the candidate new funding currencies if the yen becomes untradeable.