IBM Stock Plunges 13% as AI Tool Threatens Its Core Mainframe Business
International Business Machines shares suffered their worst single-day drop in years Monday. Tumbling nearly 13.2% after revealing that its lucrative mainframe business could be the next casualty of artificial intelligence disruption.
The steep sell-off came after Anthropic announced that its AI-powered coding tool. Claude Code, can now modernize legacy COBOL systems — a service that has long been a reliable revenue generator for IBM.
Shares closed at $223.35, erasing billions in market value and bringing the stock’s year-to-date decline to more than 24%.
The COBOL Connection
At the heart of Monday’s market panic is a programming language. It predates the internet, color television, and even the invention of the microchip.
COBOL (Common Business-Oriented Language) was developed in the late 1950s and still powers the backbone of global finance. According to Anthropic, an estimated 95% of ATM transactions in the United States run on COBOL. The language also handles massive volumes of payment processing, retail transactions, and government systems worldwide.
“Hundreds of billions of lines of COBOL run in production every day. Powering critical systems in finance, airlines, and government,” Anthropic wrote in a blog post Monday. “Despite that, the number of people who understand it shrinks every year.”
This shrinking expertise has created a perfect opportunity for AI disruption — and a perfect storm for IBM.
How Claude Code Changes the Game
IBM has built a significant business around helping large organizations. Modernize their aging COBOL systems, typically running on the company’s mainframe platforms. The process has traditionally been painstaking, expensive work requiring specialized knowledge that grows scarcer by the year.
Anthropic claims Claude Code can accomplish in hours what once took human analysts months.
“AI excels at streamlining the tasks that once made COBOL modernization cost-prohibitive,” the company said. Its tool can map dependencies across thousands of lines of code. document complex workflows, and identify system risks that “would take human analysts months to surface.”
The equation is simple: if AI can modernize legacy code faster and cheaper than human specialists, companies that once relied on IBM’s professional services may now have an alternative path forward.
“Legacy code modernization stalled for years because understanding legacy code cost more than rewriting it,” Anthropic noted. “AI flips that equation.”
A Growing Pattern of AI Disruption
Monday’s sell-off marks the second time in a week that Anthropic has sent shockwaves through the technology sector. On Friday, the company unveiled Claude Code Security, a feature that scans codebases for vulnerabilities and flags software issues for human review. That announcement triggered a broad decline in cybersecurity stocks as investors worried about the future of manual code auditing.
The cybersecurity sector remained under pressure in Monday’s trading, reflecting growing anxiety about which traditional tech services might be rendered obsolete by rapidly advancing AI capabilities.
Traders described the environment as “sell first and ask questions later” — a volatile pattern that has punished companies perceived as vulnerable to AI disruption, even when the actual threat remains years away from materializing.
Technical Debt and Digital Transformation
Anthropic framed its latest announcement as part of a broader effort to address what technologists call “technical debt” — the accumulated cost of taking shortcuts in software development that leads to increased maintenance headaches down the road.
The company argues that legacy code modernization has stalled across industries because understanding old systems has become prohibitively expensive. By automating the exploration and analysis phase, AI tools like Claude Code could unlock billions in value by helping organizations finally modernize systems they’ve long wanted to update but couldn’t afford to touch.
For IBM, which has successfully monetized those modernization challenges for decades, the implications are profound.
What’s Next for Big Blue
With shares now down more than 24% year-to-date, IBM faces mounting pressure to articulate how it will adapt to an AI-powered future. The company has invested heavily in its own AI initiatives, including its Watson platform, but Monday’s sell-off suggests investors remain skeptical about the company’s ability to defend its traditional strongholds.
IBM did not respond to requests for comment on how Claude Code might impact its mainframe business or what countermeasures it might deploy.
For now, the company joins a growing list of established tech players learning a harsh lesson of the AI era: in a landscape changing this quickly, no business line is truly safe — no matter how old the code it’s built on.