Enterprise IT + startup pilots (2023–2025 pattern) · 2024 · cost index 3/5
AI codebase rewrite pilots that shipped nothing
Six-figure LLM API and SI costs; production cutover: zero
What happened
Exec decks promised autonomous COBOL-to-microservices migration "by Q3." Teams fed repos to copilots, generated plausible diffs, and discovered the model hallucinated APIs their mainframe never had. Pilots looked great in demos with 500-line samples; production needed tests nobody had.
Failure mode
Treating probabilistic codegen as accountability-free migration. No strangler plan, no parity tests, no owner for edge cases in the legacy module the model never saw. "AI rewrite" became a synonym for skipping the hard organizational work.
Lesson
LLMs accelerate typing, not ownership. Use them inside a migration strategy you would trust with interns: small slices, verified behavior, humans on the hook for prod. Autopilot slides lie; diffs do not deploy themselves.
Sources
- Gartner — AI-assisted modernization cautions
- Industry pilot reports — LLM migration POC abandonment
- Joel Spolsky — Things You Should Never Do (still relevant)
Related tech
Practice · 2023–now
AI will rewrite the codebase
Big-bang rewrite, now with a chatbot. Same failure mode; prettier slides.
$ Exec decks promised autonomous migrations "by next quarter." Teams that skipped tests, ownership, and incremental strangler patterns bought expensive demos and fragile diffs.
Practice · 2021–now
AI pair programming
Autocomplete that actually understands the file. Changing how code is written faster than how it's reviewed.
Framework · 2023–now
LLM app frameworks
Chains, agents, and prompt wrappers shipping weekly. The durable pieces will be boring: evals, retrieval, and product UX.
Practice · 1995–now
Big-bang rewrite
Replace the working system instead of strangling it. A perennial money pit with new branding each decade.
$ "We'll freeze features and rewrite in the hot language." Multi-year projects shipped late, incomplete, or not at all — while competitors iterated on the ugly system that made money.
Architecture · 2012–now
Microservices Everywhere
Independent deployability as religion. Correct for some; ruinous cargo-cult for most.
$ Teams split 4-person products into 40 services, then hired SREs to babysit the mesh. Many later consolidated — after years of distributed tracing invoices and on-call trauma. See case studies on premature microservices and big-bang cutovers for named failure modes.
Language · 1995–now
Java
Write once, run everywhere — then enterprise forever. Still the backbone of serious backend estates.