SoftBank Group Corp. plans to boost its interest in OpenAI by acquiring up to $1.5 billion in shares from the startup's employees, according to people familiar with the situation.

The Japanese corporation will make a tender offer for the stock, allowing OpenAI staff to cash in their shares if they like.

SoftBank committed $500 million to OpenAI's $6.6 billion fundraising round in October, but had pressed for a higher contribution at the time, according reports.

Masayoshi Son, the founder of SoftBank, has assured to boost investments in AI as his Tokyo-based business recovers from years of poor management. In its most recent fundraising round, OpenAI, which took the lead in the industry early on with its ChatGPT, was valued at $157 billion.

It's unclear how much stock SoftBank will be able to purchase from OpenAI's employees, who may choose to keep their shares if they see promising future prospects.

SoftBank and OpenAI did not reply to calls for comment after normal business hours. According to reports, the SoftBank tender offer will close this week.