Palantir stock closed slightly up on Thursday, after declining for six straight sessions. Palantir's pullback raised questions over whether the AI stock boom is winding down.

In recent days, Palantir's stock has been showing signs of slowing down. After hitting a new all-time high of $190 on Aug. 12, it has proceeded to trade lower. By Monday, the AI stock would close at just over $174 -- down 8% from its recent high.

That rise has made Palantir extremely pricy. Shares now trade at a multiple of 214 times expected earnings over the next 12 months, compared to an S&P 500 average of 22 times earnings.

Palantir Technologies Inc. (NASDAQ: PLTR) is one the AI Stocks Analysts Are Watching Closely . On August 18, Palantir stock received a cautious mention from Citron regarding the company’s stock valuation, marking the second time the firm has raised concerns.

Two hedge fund managers with a track record for market beating returns sold Nvidia and bought Palantir in the second quarter.

Citron Research, the firm led by short-seller Andrew Left, unpacked its bear case for Palantir, using OpenAI to show why it may be highly overvalued.

Palantir shares tumbled Tuesday afternoon, extending recent losses as a high-profile short seller fueled worries the stock could be overvalued after a strong run earlier this year.

Palantir ( PLTR -5.81%) stock is getting hit with another substantial round of sell-offs Wednesday on the heels of a big valuation pullback in yesterday's trading. The artificial intelligence ( AI) leader's share price was down 7% as of 11:15 a.m. ET and had been down as much as 9.8% earlier in trading.