OpenAI is offering employees the chance to sell up to $1.5 billion worth of shares to Japan's SoftBank Group.The transaction is expected to close by 24 December, aligning with OpenAI's valuation of $157 billion.SoftBank, through its Vision Fund 2, aims to deepen investments in AI by acquiring OpenAI shares.This move follows SoftBank's $500 million investment in OpenAI during a $6.6 billion funding round in October.