US cybersecurity software stocks ​tumble after Anthropic announces it is 'scared' of launching new, powerful AI model

Anthropic's newly announced AI model, Mythos, has sent shockwaves through financial markets, triggering a fresh sell-off in US software stocks and reigniting fears that artificial intelligence (AI) can disrupt the industry faster than it can handle. The catalyst is Anthropic's powerful new AI model, called Claude Mythos, which the company has decided against a wide public release after determining it could expose hidden cybersecurity vulnerabilities that have existed, undetected, for years. The company says that the AI model is so powerful that its access has been restricted to a group of approximately 40 major technology companies, including Microsoft and Google. This has led to a drop in shares of major cybersecurity companies including Zscaler, Cloudflare, Okta and CrowdStrike, among others, according to news agency Reuters.The S&P 500 Software and Services Index fell 2.6% on Thursday (April 9) - the index is now down 25.5% since January - one of the worst-performing segments of the US market in 2026, Reuters said. Cybersecurity firms were among the hardest hit, with Cloudflare, Okta, CrowdStrike and SentinelOne all dropping between 4.9% and 6.5%. Reuters said that Zscaler was among the biggest decliners on the entire S&P 500, falling 8.8% after brokerage BTIG downgraded the stock from "buy" to "neutral", citing concerns over demand and rising competition. Enterprise software names such as Atlassian, Workday, Adobe, Salesforce and Intuit, all dropped between 3.7% and 6.8%. The sell-off also spread to Europe, where SAP, Capgemini and Temenos fell between 3% and 7%.The market's reaction was not simply about one unreleased AI model. It was about what that model's existence implies - if AI can find vulnerabilities that cybersecurity companies have missed for years, what exactly are those companies selling?"We're getting back to being concerned about the prior software-specific concerns stemming from AI and private credit that are coming back to the fore," said Sosnick, chief market analyst at Interactive Brokers, was quoted as saying.Wednesday (April 8) had offered the software sector a temporary escape after optimism surrounding a US-Iran ceasefire which lifted broader market sentiment.In January, Anthropic launched 11 open-source plugins for its Claude Cowork tool, triggering what analysts called a 'SaaSpocalypse' - a brutal selloff that wiped out roughly $285 billion from software, legal tech and financial services stocks in a single trading session.