The Nikkei broke 65,000 for the first time on Monday, and SoftBank, the listed proxy for both OpenAI and Arm, did much of the lifting.
SoftBank Group shares hit a record high in Tokyo on Monday, carrying the Nikkei 225 above 65,000 for the first time and capping a fortnight in which the Japanese investment conglomerate has added more than $60bn to its market value.
The lift came almost entirely from a single source: growing conviction that OpenAI is days away from filing for an initial public offering that would crystallise the largest single bet Masayoshi Son has ever made.
The Nikkei finished the morning at 65,254, up 3.02% on the session, according to The Japan Times. Easing tension between the United States and Iran, and the prospect that shipping through the Strait of Hormuz will resume, gave the broader market a tailwind.
The SoftBank-specific rally, however, has been running since Thursday, when reports first emerged that OpenAI was preparing to file confidentially for an IPO as soon as the end of last week, targeting an autumn debut at a valuation that could exceed $1tn.
