Anthropic's release of COBOL-specific AI functionality triggered a 13% stock drop for IBM, its worst day in 26 years. The AI bot's ability to write 67-year-old COBOL code threatens IBM's decades-long monopoly on maintaining the critical, aging systems underpinning banks, airlines, and government.

IBM's stock fell 25% month-over-month, reflecting investor alarm over the tech giant's potential loss of control over essential, yet outdated, enterprise infrastructure. The move directly challenges IBM's lucrative service model, where clients pay premium fees for mainframe support and system modernization guidance.