Cybersecurity stocks were falling sharply on Thursday after the sector rebounded earlier in the week, boosted by a new Anthropic project.

Palo Alto Networks was down 3.9%, CrowdStrike Holdings was off 7.5%, Zscaler tumbled 11%, SailPoint dropped 11%, and Fortinet slid 3.4%.

The cybersecurity sector has been in a slump this year as some on Wall Street are worried about the impacts artificial intelligence will have on it. Aside from concerns that improving AI models can replace critical software functions, some investors are focused on how AI, and the implementation of AI agents, introduces more complex security challenges. The worry is that not all security firms will be able to handle new threats.

Anthropic announced a partnership called Project Glasswing on Tuesday, which alleviated some fears. The AI start-up is giving a collection of technology companies access to its Claude Mythos Preview model to defend critical software. Palo Alto and CrowdStrike were included as members in this partnership, which led analysts to believe the companies are in a good position to work through complex security concerns.

Palo Alto stock has gained 3.2% this week while CrowdStrike has risen 2.3%. Other cyber stocks saw a momentary lift the week, but that optimism didn’t last long.

“The winners in an AI-centric security world will be those that can re-architect products around AI workflows rather than simply bolting AI features onto legacy tools,” William Blair analyst Jonathan Ho wrote in a note on April 8.

Right now, there are no winners.