ChatGPT-owner OpenAI is allowing its employees to sell roughly $1.5 billion worth of shares in a new tender offer to Japan's SoftBank Group, CNBC reported Wednesday, citing two people familiar with the matter.

The report comes after Microsoft-backed OpenAI completed a $6.6 billion funding round from investors, including SoftBank in October at a valuation of $157 billion.

The Information reported that the Japanese conglomerate had already invested $500 million in the AI company.

CNBC said the new financing was spurred by SoftBank's billionaire CEO Masayoshi Son, who was persistent in seeking a larger stake in the startup after investing in its last funding round.

The tender offer is set to close this week and will allow current and former OpenAI employees to cash out their shares, according to the report.

OpenAI and SoftBank declined to comment on the report to CNBC.

They did not immediately respond to a Reuters request for comment.