The Yen's Strongest Week Since September: Separating Haven Flows, Options and Inflation in USDJPY

Key takeaways

1. The yen rose 0.3% to 156.28 per dollar in Asia on Friday, its strongest level in more than a month, and was set for a 1% weekly gain (Reuters).

2. At least four drivers overlapped: an AI-led equity sell-off, the largest one-day fall in the US 10-year yield since March 2023, large option expiries and core inflation back above 2% in Japan.

3. Before you explain a large session move with one headline, list every driver and ask which of them will still be present next week.

The development

USDJPY fell on Thursday from 158.25 early in the session to 156.69 on EBS by the New York close, and extended the slide to 156.08 in early Asia on Friday before steadying (Reuters). In Asian trading on Friday the yen was 0.3% firmer on the day at 156.28, its strongest level in more than a month and on course for its largest weekly gain since early September (Reuters).

The same night, Japan's Statistics Bureau reported at 23:30 UTC that core consumer prices, which exclude fresh food, rose 2.1% in September from a year earlier, up from 1.7% in August. The measure excluding fresh food and energy rose 2.4%, from 1.9% (Statistics Bureau of Japan). Core inflation matched the Reuters poll (CNBC).

Market transmission

Reuters linked the move to several sources at once:

• Risk aversion. The Nasdaq fell 2.6% on Thursday on doubts about AI spending, and Japan's Nikkei was down 1.3% on Friday and about 5% on the week. Foreign investors who sell Japanese shares often unwind the related currency hedges, which means buying yen.

• Rates. The US 10-year yield fell from 5.13% to 4.96% on Thursday (US Treasury), its biggest one-day decline since 10 March 2023 (CNBC). Narrower US-Japan yield spreads reduce the reward for holding dollars against yen.

• Options. About $9.1 billion of options struck on the 157 handle expired on Thursday, and sellers of yen calls had to buy yen as the spot rate fell (Reuters).

• Policy. Exporters kept selling dollars into rallies, and the CPI data supported the case for a Bank of Japan (BoJ) hike, although most economists polled by Reuters expect a hold on 30 October and a quarter-point increase in December.

What to monitor next

• Whether London, from 07:00 UTC, extends the move or treats it as an Asia and New York story.

• Further option expiries on Friday, about $2.1 billion at 154.95–155.00 and $1.5 billion at 157.00 (Reuters).

• The US flash PMIs released at 13:45 UTC, which showed selling prices rising at the fastest rate since August 2022 (S&P Global), and the 10-year yield around the 5% level.

• Any official comment from Tokyo on the pace of yen moves ahead of the BoJ meeting on 29–30 October.

Reusable lesson

A large move rarely has one cause. Separate the drivers into those that fade, such as option expiries and month-end or hedge flows, and those that persist, such as a change in rate expectations. If most of the move came from the fading group, the move is more likely to retrace when those flows end. If it came from repricing, it tends to last longer.

Invalidation and risk

A rebound in technology shares would remove the haven bid quickly. If US yields climb back above 5%, as ING expects eventually, the rate driver reverses. A cautious BoJ statement next week could also disappoint markets that have moved early.

Glossary

Option expiry: The point at which an option contract lapses; hedging by option dealers near large strikes can push spot towards or away from those levels.

Core-core CPI: Japanese consumer prices excluding fresh food and energy, a gauge the BoJ watches for demand-driven inflation.

Haven currency: A currency, such as the yen or Swiss franc, that investors tend to buy when risk appetite falls.

Sources

Reuters (via Euronext Live) (2026-10-23): Yen shines as AI jitters spur safe-haven rush

Reuters (via Euronext Live) (2026-10-23): Asian shares wobble as tech rout boosts bonds, dents rate hike bets

Reuters (via eFXdata) (2026-10-23): USD/JPY - Mini-perfect storm sends USD/JPY down 3 big figures

Statistics Bureau of Japan (2026-10-23): Consumer Price Index, Japan, September 2026 (2025 base)

CNBC (2026-10-23): Japan core inflation in September surges to its highest this year at 2.1%

US Department of the Treasury (2026-10-22): Daily Treasury Par Yield Curve Rates

Disclaimer

This note is provided by the SummitFx Project for general education and market context only. It is not investment advice, not a solicitation to buy or sell any instrument, and not a personal recommendation. Foreign exchange and related markets are leveraged and can result in the loss of some or all of your capital. Figures are believed accurate at the time of research and may already be stale. Always verify live prices, official releases, and your own risk limits before acting. Past market behaviour does not determine future results.