Has AI really solved legacy migrations?

Back in February, Anthropic published a post about COBOL, and IBM lost 13% of its value in a single day. For a few days it felt like the question of legacy migration had been answered: with AI, migrations that used to take years would take quarters. A few months later, I wanted to see what actually happened.

It turns out the story is more nuanced than the headlines. The post was about understanding COBOL code, not about migrating it automatically, and IBM recovered. I read some of the announcements that followed, but I have not seen anyone say they migrated a large system by clicking a button. Morgan Stanley and Toyota, for example, used AI to understand the old system, which is very useful but is a different thing. And Gartner now expects more than 70% of the mainframe exit projects started in 2026 to fail, because people overestimate what generative AI can do on its own.

I don’t want to be dismissive: AI has changed how we work on migrations, and saying otherwise would be silly. But the programming language is the smaller part of the problem. Around it there are things like batch jobs, transaction monitors and data encodings. And above all there are decisions to make: how things work inside the organization, which technologies are in use, how to get from what you have to where you want to end up, where to break compatibility with the old world, and how to show that the new system behaves like the old one. These are choices that need someone who thinks them through, gathers context from the people who know the system, and takes responsibility for the result.

So I recorded a short series of four videos, Migration Blueprint, on how to plan a legacy migration (RPG, COBOL and more). The first episode is out now, and it is about exactly this question:

https://www.youtube.com/watch?v=65Hmh4NC2es

The other three will be published on our YouTube channel on the coming Tuesdays:

• 20 October: RPG to Java, Python or C#? It’s hard to get it wrong
• 27 October: How to prove your migrated system does the same thing
• 3 November: Migrate first, re-architect later

If you are looking at a migration, or you went through one, I’d like to know what worries you the most. You can tell me by sending me an email.