TOKYO -- SoftBank Group has been among the top performers on Tokyo's top-tier Prime market this year, surging on the back of a U.S. tech rally powered by an artificial intelligence boom.

SoftBank Group Chairman Masayoshi Son. Along with expectations for the company's future growth, investors are buying the company's shares as a way to gain access to OpenAI. (Nikkei montage/Source Photo by Nanami Sato)
Investors hopeful of future growth, but rising AI exposure a source of concern