The yen strengthened as far as JPY152.90 to the dollar at one point on September 8, its firmest level in about seven months, The Yomiuri Shimbun reported on September 8. Buying was driven by growing expectations in the market that the Bank of Japan will speed up the pace of its interest rate increases.

The move extends a sharp reversal for a currency that spent much of the year under pressure. Before Japan and the United States intervened jointly at the end of July, the yen was trading in the JPY163 range, meaning it has gained roughly JPY10 in a little over a month.

By 5pm in Tokyo, most trades were being settled at JPY153.80-82 to the dollar, up JPY1.75 from the same time the previous day. In later New York trading, the currency eased back to the low JPY154 range.

The yen also advanced against other currencies, closing most Tokyo trade at JPY178.60-64 per euro, a gain of JPY2.20.

Some market participants attributed the acceleration to speculators unwinding short yen positions. The closure of US markets on September 7 for a public holiday left fewer participants in the market, making price swings larger.

Japanese authorities had already stepped into the currency market from late April into May, buying yen to counter its weakness, before the joint action with Washington at the end of July. Those efforts repeatedly ran into what traders called the JPY155 wall, a psychological threshold that pushed the currency back towards JPY160 after each intervention.

That barrier has now given way, with coordinated Japanese and US action combined with expectations of faster BOJ tightening. US Treasury Secretary Scott Bessent said on August 30, in a meeting with BOJ Governor Kazuo Ueda, that he strongly supported policies aimed at correcting the yen's weakness.