Adds comment from Altman in paragaph 8

By Sam Nussey

TOKYO, Feb 3 (Reuters) - SoftBank Group 9984.T CEO Masayoshi Son on Monday said he has agreed with OpenAI CEO Sam Altman to set up a joint venture in Japan to offer artificial intelligence services to corporate customers.

The joint venture, SB OpenAI Japan, will be owned by OpenAI and a company established by SoftBank and its domestic telecoms arm.

The Japanese investment giant will also pay $3 billion annually to use OpenAI's technology across SoftBank group companies.

Son is moving to deepen his exposure to OpenAI, with SoftBank looking at investing $15 billion to $25 billion in the company, Reuters reported last week.

SoftBank is also committing $15 billion to Stargate, a joint venture with OpenAI and Oracle ORCL.N to build AI capacity in the U.S., Reuters has reported.

The Stargate launch last month saw Son make his second appearance with Donald Trump since his election as president in November.

China's DeepSeek has caused investors to question the billions being poured into AI technology with a model that appears to rival the capabilities of leading U.S. companies.

"The world is going to just need so much compute," Altman said.

Son's backing for OpenAI reflects his reemergence as an investment force after a period of retrenchment sparked by the falling value of SoftBank's tech portfolio and a series of high profile stumbles.

He has a long history of partnering with tech firms in the U.S., with SoftBank bringing the iPhone to Japan in 2008.

Son and Altman also met with Japanese Prime Minister Shigeru Ishiba on Monday.

(Reporting by Sam Nussey; Additional reporting by Anton Bridge; Editing by Chang-Ran Kim, Edwina Gibbs and Louise Heavens)

((sam.nussey@tr.com;))