SoftBank Group rose ¥514, or 10.3%, to ¥5,515 on the Tokyo Stock Exchange on September 4, leading the TSE Prime Market after OpenAI announced GPT-6 Astra. OpenAI CEO Sam Altman said he was "confident GPT-6 Astra is the best model in the world," reviving interest in generative AI investment themes after the company’s first major foundational-technology update since August 2025. Arm Holdings, the British semiconductor design company under SoftBank’s umbrella, saw its American depositary receipts, or ADRs (U.S.-traded certificates representing foreign shares), rise more than 3% the previous day. OpenAI and Arm account for more than 70% of SoftBank Group’s asset portfolio, tying their market performance closely to investor expectations for SoftBank’s earnings. A weaker dollar, a firmer yen and rising cryptocurrencies also supported related Japanese equities, while easing U.S. rate-hike expectations helped broader risk appetite. Other notable moves included gains in Money Forward, Metaplanet, Brandista, ABEJA, Remixpoint, KeePer Technical Laboratory, Nippon Signal and Ootoya Holdings, while JM Holdings fell after cutting its fiscal-year profit forecasts and recognizing an impairment loss. Attention now turns to the September 15–16 FOMC (Federal Open Market Committee) meeting and whether GPT-6 Astra’s commercial deployment contributes to earnings.