(Reuters) - OpenAI, the company behind ChatGPT, has raised $6.6 billion from investors, which could value the company at $157 billion and cement its position as one of the most valuable private companies in the world.

The funding has attracted returning venture capital investors including Thrive Capital and Khosla Ventures, as well as OpenAI's biggest corporate backer Microsoft and new participation from Nvidia.

The closing of the funds coincides with the company's ongoing restructuring efforts and executive changes, including the abrupt departure of its longtime Chief Technology Officer, Mira Murati, last week.

Altimeter Capital, Fidelity SoftBank and Abu Dhabi's state-backed investment firm MGX also participated in the round.

OpenAI Chief Financial Officer Sarah Friar told employees on Wednesday that the company will be able to provide liquidity for them through a tender offer to buy back their shares in the company following the funding, although no details and timing have been decided, according to a source. Earlier this year, the company allowed some employees to cash out their shares at a valuation of $86 billion.

Thrive Capital, which committed about $1.2 billion from a combination of its own fund and a special purpose vehicle for smaller investors, negotiated the option to invest another $1 billion next year at the same valuation if the AI firm hits a revenue goal, sources added.

Apple which was in talks to invest in OpenAI, did not end up joining the funding, sources said, who requested anonymity to discuss private matters. Apple did not immediately respond to a request for comment.

The funding came in the form of convertible notes, and the conversion to equity hinges on a successful structural change into a for-profit that would no longer be controlled by the non-profit board and the removal of cap on returns for investors.

The personnel changes haven't deterred enthusiasm from most investors, who are anticipating significant growth based on the projections by OpenAI CEO Sam Altman.