Ken Griffin of Citadel in a letter to clients on Friday addressed the firm's purchase of assets from Leopold Aschenbrenner's Situational Awareness hedge fund. 

According to a letter obtained by CNBC's Sara Eisen, Griffin told clients that Citadel has unwound more than 80% of the aggregate risk from the original portfolio purchased by conducting more than 100 block trades over $4 billion in market value.

Griffin detailed in the letter that Citadel entered discussions with Situational Awareness to acquire some of the fund's holdings on July 29. One day later, CNBC's David Faber reported that Situational Awareness was forced to sell all of its public stock positions after facing steep losses. Citadel was later revealed as the buyer of the assets.

"A transaction of this magnitude could not have been completed without the extraordinary cooperation of the trading and prime brokerage teams at the banks serving both firms," Griffin wrote in the Friday letter to clients. "I am grateful for the focused effort they brought to the rapid transfer of the portfolio."

Griffin also confirmed the firm's flagship multistrategy Wellington fund returned 5.94% in July, which CNBC previously reported marked the fund's best monthly performance since 2022.

Situational Awareness as a hedge fund concentrated positions in the artificial intelligence trade, on a belief by 25-year-old Aschenbrenner that the technology would fundamentally reshape the world and the economy. At the same time, the fund had short positions in some software companies, a sector that investors have worried will be disrupted by AI.

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