Anthropic's AI Triggers $285 Billion Market Sell-Off

The sell-off was reportedly triggered by a markdown file, not a commercial product or platform, that demonstrated a significant leap in AI capabilities, according to Hacker News Newest. The file, approximately 200 lines in length, served as a technical proof-of-concept that dramatically altered market perceptions of the competitive landscape for enterprise software.

This event coincides with the release of Anthropic's Claude Opus 4.6, a new AI model that CNBC reports is pushing the industry toward an era of "vibe working." The model's capabilities were starkly illustrated in a separate, costly experiment documented by The Register. According to their reporting, the Claude Opus 4.6 model was tasked with writing a C compiler, an ambitious and complex software engineering project. The AI agent successfully built a compiler that "mostly works," but the project's creator was reportedly worried by the endeavor, which consumed an estimated $20,000 in computational resources to complete.

This demonstration of autonomous, high-cost software development sparked immediate concern among investors. The ability of an AI agent to undertake such a sophisticated technical project, even inefficiently, suggested a future where AI could potentially automate core, high-value engineering tasks. This realization prompted a rapid repricing of software companies whose valuations were predicated on the scarcity of human coding talent and the complexity of their technical products. The market’s violent reaction indicates a fear that the fundamental business models of the entire sector are more vulnerable to disruption than previously believed.

The sell-off was further contextualized by an accelerated and heated development cycle among leading AI firms. As noted in the AlphaOfTech Daily Brief, Anthropic and OpenAI have recently turned heads with their latest model releases, "sparking heated discussions about rushed AI development cycles and their repercussions on trust and privacy." This breakneck pace of innovation, while showcasing rapid progress, also introduces significant uncertainty and risk, factors that financial markets are inherently averse to.

Adding a layer of intrigue to the event is the internal turmoil suggested by a separate report. A post on Fosstodon’s AI timeline highlighted that an Anthropic researcher, who was leading the company's Safeguards Research Team, recently quit and published a cryptic public letter. According to the post, the researcher’s work involved exploring "the causes of AI sycophancy," developing defenses against “AI-assisted bioterrorism,” and writing “one of the first AI safety cases.” His departure under mysterious circumstances, described with terms like "AI Psychosis," raises profound questions about the internal assessments of AI development risks at the highest levels, potentially exacerbating investor unease about the stability and long-term safety of the technology they are investing in.

The confluence of these factors—a tangible demonstration of disruptive AI capability, a frenetic and potentially reckless competitive pace, and internal warnings from safety researchers—created a perfect storm of market anxiety. The result was a historic single-session sell-off that erased hundreds of billions in market valuation. The event signals a new era of market sensitivity to AI breakthroughs, where technical demonstrations contained in simple documents can have immediate and severe financial consequences, forcing a reassessment of value across the global technology sector.