Anthropic’s Claude Code modernizes COBOL and IBM shares plunge about 13%

Anthropic announced Monday that its Claude Code tool can be used to streamline and modernize decades-old COBOL systems, and investors responded with a sharp selloff in IBM stock that several outlets tied directly to the announcement. Reports differed on the exact magnitude, with some saying IBM shares fell over 10% while others put the decline at about 13.2%; CNBC reported the stock closed nearly 13.2% lower at $223.35 per share.

Anthropic framed the work as an overturning of a long-standing economic equation in legacy-code projects. In a blog post quoted by multiple outlets, the company wrote, "Modernizing a Cobol system once required armies of consultants spending years mapping workflows." Anthropic added that "tools like Claude Code can automate the exploration and analysis phases that consume most of the effort in Cobol modernization" and argued that "legacy code modernization stalled for years because understanding legacy code cost more than rewriting it. AI flips that equation."

The company and reporting outlets highlighted concrete capabilities: Claude Code, also described as Claude AI in some coverage, can purportedly reconstruct developer intent from undocumented code, map dependencies across thousands of lines of code, document workflows and identify risks "that would take human analysts months to surface." Anthropic and CNBC noted the scale of the problem: "Hundreds of billions of lines of COBOL run in production every day, powering critical systems in finance, airlines, and government," and Anthropic asserted that an estimated 95 percent of U.S. ATM transactions still rely on COBOL.

Those technical claims landed against a business reality that has sustained IBM's mainframe and services divisions for decades. A large share of mission-critical COBOL workloads run on IBM mainframes, and IBM has long offered tools and consulting to help clients modernize or integrate those systems. Techzine Global reported that IBM "highlighted its own technological strengths" after the spike in selling, and Jefferies told investors that the long-term threat may be "less severe than investors perceive," pointing to IBM's broader hybrid cloud, AI and data business.

Market commentators and social platforms framed the move as another episode in AI-linked software volatility. Some outlets and market posts characterized the IBM decline as the company's worst single-day drop since October 18, 2000; other reporting compared it to steep moves in March 2020. Times of India cited Bloomberg data saying that, after the slide, IBM shares were down 26 percent for February, putting them on course for their largest monthly percentage decline since at least 1968.

Beyond the market gyrations, the episode raises questions about continuity and equity in public services and financial access. If Claude Code delivers on its promise, organizations that rely on legacy systems could reduce modernization schedules from years to quarters, Anthropic and commentary suggest. That could lower costs and speed updates to critical back-end systems that affect payments, government benefits and other services relied upon by many communities. At the same time, rapid automation of legacy maintenance threatens a business line that supports employment in systems modernization and may concentrate more influence with a handful of AI vendors.

Key open questions remain: the full text and technical detail of Anthropic's blog post, IBM's formal response and an exact reconciliation of intraday and closing price data and historical comparisons. Those details will be central to assessing whether Claude Code represents a structural shift in how institutions manage legacy code or a disruptive announcement that is provoking a short-term market repricing.