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OpenAI CFO Sarah Friar is looking to reassure its investors that the richly valued artificial intelligence startup is still in a strong position and is poised to close a big funding round soon, despite losing top talent this week.

In an email to OpenAI's investors seen by CNBC, Friar addressed the departure of Chief Technology Officer Mira Murati, who announced her departure on Wednesday. Later that day, Sam Altman said two top research executives, Bob McGrew and Barret Zoph, were also leaving.

"I wanted to personally reach out following the news of Mira's departure from OpenAI," Friar wrote in the letter, which was viewed by CNBC. "While leadership changes are never easy, I want to ensure you have the full context."

Friar added that, "We are incredibly proud of everything she's helped build," and said the San Francisco-based company still has a "talented leadership bench" to compete.

OpenAI, which is backed by Microsoft and recently partnered with Apple on its AI for iPhones, is in the midst of closing a $6.5 billion funding round, which should value the company at roughly $150 billion, according to sources familiar with the matter. Thrive Capital is leading the round, and plans to invest $1 billion, according to sources.

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