The divergence on Wall Street sets up a likely split in Tokyo, where AI-linked heavyweights could trail even as the broader market draws support from strong global risk appetite. Falling oil is a modest positive for energy-importing Japan, but a weaker dollar raises the prospect of a firmer yen, a headwind for exporters. The BoJ minutes add a second potential yen driver before the cash open. Traders looking for a relative-value signal will focus on the Nikkei-Topix spread, which tends to widen when AI and chip names diverge from the rest of the market.---Arm shares fall 5% after hours despite Q2 beat as outlook only edges past forecasts---Wall Street gave Tokyo a strong lead, just not for the stocks the Nikkei leans on most.Summary:Arm fell about 5% in the regular session and slid further after hours despite beating Q2 forecastsUS indexes rallied sharply on Wednesday, with the Dow up about 1,570 points, but AI infrastructure stocks fell, with Nvidia down about 3% and Micron and Marvell down around 7%The selloff was linked to concern that tighter restrictions could slow data centre expansionSoftBank holds roughly 90% of Arm and has been among the biggest single drivers of the NikkeiThe price-weighted Nikkei is more exposed to an AI selloff than the broader TopixA weaker dollar and the BoJ minutes add a yen dimension to the sessionSoftBank Group goes into Thursday’s Tokyo session facing pressure from two directions: a post-results slide in Arm Holdings, which it controls, and a sharp rotation out of AI and chip stocks on Wall Street that left the broader market higher but the AI trade under strain.Arm shares fell about 5% in the regular session and were around 4% lower again after hours, even though the chip designer beat expectations for its fiscal second quarter. Adjusted earnings per share came in at 52 cents against forecasts of 47 cents, and revenue of about $1.44 billion topped estimates near $1.38 billion. Guidance for the current quarter only edged past consensus, however, and annualised contract value, a measure of licensing commitments, was marginally below expectations.The regular-session drop fits a wider pattern. US indexes rallied strongly on Wednesday, with the Dow surging about 1,570 points, or roughly 3%, as markets weighed the implications of Democrats winning both chambers of Congress, according to investingLive. The gains were broad, helped by lower Treasury yields, a weaker dollar and falling oil. AI infrastructure stocks went the other way: Nvidia fell about 3%, while Micron and Marvell lost around 7%, amid concern that tighter restrictions could slow data centre expansion and the spending that supports chip suppliers.That combination matters for Japan because of ownership and index structure. SoftBank holds roughly 90% of Arm, and it has become one of the most influential stocks in the Nikkei 225. It overtook Toyota as Japan’s most valuable company in June, when its rally was the largest single contributor to the index topping 67,000 for the first time. In May, a roughly 5% fall in SoftBank made it the biggest drag on the index.Because the Nikkei is price-weighted and leans heavily on high-priced, AI-linked names, it is more exposed to a selloff in that theme than the broader, market-capitalisation-weighted Topix. A session in which most stocks rise while AI heavyweights fall could therefore leave the Nikkei lagging the wider market.The yen is a further variable. A weaker dollar can lift the Japanese currency, which tends to weigh on exporters, and the Bank of Japan’s September meeting minutes are due shortly before the cash open.Arm’s upbeat commentary offers some offset, with purchase orders for its AGI CPU data centre processor extending through calendar 2027. The key question is whether SoftBank absorbs both hits in full, and how wide the gap between the Nikkei and the Topix becomes. This article was written by Eamonn Sheridan at investinglive.com.