I wonder how true that is, vs customers using AI to port projects off big iron, or to many work that they’d previously outsourced to Big Blue. I suspect it’s only going to get easier to migrate to cheap servers running modern languages, which can’t be great news for companies that highly depend on lock-in.

This is such a nonsense take. You have no idea how the companies that use mainframes actually operate. There's no world in which they will vibecode a solution.

>There's no world in which they will vibecode a solution.

It's not like the Bank of Americas of the world are going to get an Anthropic or OpenAI API key, and then use the prompt "move this off of COBOL please". They'll either hire a contractor who'll work out how to best utilize AI to migrate the existing codebase off of mainframes, or spin up an internal team to do the same thing.

You've still no idea. Who is going to certify it? No auditor will certify vibe coded slop. Who will provide the indemnity for it? No insurer will touch it. It doesn't even save significant money. The cost of writing the code is a tiny fraction of the total cost of ownership.

So in your thesis, auditors and insurers will happily accept the intractable nightmare of mainframe code hacked together over multiple decades, often by the lowest-cost outsourced development shop and with the original creators now long retired, but they'll refuse modern, readable, testable code because it was generated partially by AI?

I've worked on the type of legacy IBM systems being discussed here. They're often filled with absurd hacks. VMs running outdated operating systems on emulated hardware because that was cheaper than updating the application. Systems so confusing and poorly documented that only a single employee knows how to update it. Known bugs in software that are solved by pre-processing or post-processing inputs/outputs to hack around the issue.

"Vibe coded slop" isn't going to be any worse than "IBM-outsourced slop" or "Maintained by one quirky IT guy for 15 years slop"

AI is good at coding if there's an oracle. If the system is ancient, unreadable, untestable, that's exactly the opposite. It won't get the exact set of corner cases.

You're absolutely right!

.... and that's because the mainframe industry is so heavily gatekept that the information feels practically word-of-mouth between a circle of old greybeards that don't want to let the kids touch it.

Always wanted to even get my hands on ZD&T but IBM never thought I was worthy enough.

Press release: https://newsroom.ibm.com/2026-07-14-Arvind-Krishnas-Letter-t...

Current title too kind to IBM...real title is: "IBM stock craters 23% after issuing second-quarter earnings warning"

Some later discussion: https://news.ycombinator.com/item?id=48907665