Mira Murati, the chief technology officer of OpenAI, has resigned from the company after 6.5 years.  The resignation is part of a wide-ranging change in OpenAI leadership that also includes the departures of Ilya Sutskever, John Schulman and the extended leave of absence of Greg Brockman.  Sam Altman, CEO of OpenAI, praised Moratti's important role in transforming the company from an unknown research lab to a leading institution in artificial intelligence.  At the same time, OpenAI is in talks to raise new capital, which could increase the company's value to $150 billion.