Jim Simons' RenTech fund quadrupled its Tesla stake last quarter - and boosted its AMC bet by 38%

• Jim Simons' RenTech quadrupled its Tesla stake and grew its AMC position by 38% last quarter.
• The quantitative hedge fund's AMC position still fell in value as the stock price slumped.

Renaissance Technologies quadrupled its Tesla stake and boosted its AMC Entertainment bet by nearly 40% in the third quarter, Securities and Exchange Commission filings show.

RenTech, one of the biggest and best-performing hedge funds in history, increased its Tesla holdings from about 204,000 shares to 814,000 shares. The electric-vehicle company's stock price jumped 14% last quarter, meaning the value of RenTech's position surged by about 360% to $631 million. As a result, Tesla was the fund's 13th most-valuable holding as of September 30, up from 106th on the list at the end of June.

The quantitative hedge fund, which was founded by former NSA codebreaker and MIT math professor Jim Simons, also bolstered its AMC position from 1.8 million shares to 2.5 million shares. However, the movie-theater chain - a firm favorite of meme-stock traders - suffered a 33% drop in its stock price last quarter. The value of RenTech's stake shrank by 7% to $95 million as a result.

Notably, RenTech slashed its Tesla position by 75% in the three months to June 30, suggesting it warmed up to Elon Musk's automaker last quarter. Meanwhile, the fund had already tripled its AMC holdings in the second quarter, indicating it grew even more bullish on the stock last quarter.

RenTech has held larger positions in both companies in the past. For example, it owned a split-adjusted 20 million Tesla shares at the end of 2019, which would be worth more than $20 billion today. It also held nearly 3.5 million AMC shares at the half-year mark in 2019, which would have fetched about $250 million when AMC's stock price peaked in May of this year.

The hedge fund, which employs algorithms to determine most of its trades, counted a $2.1 billion stake in Novo-Nordisk, a $1.2 billion stake in Atlassian, and a roughly $950 million position in Verisign as its top three holdings at the end of September.