The migration strategy of the future

I had an insight today that changes how I think about platform migrations.

I have been building a proof of concept with microfrontends, hosting Auth0 components in a Vue shell that pulls in our Vue-based platform natively and embeds our Angular-based platform alongside it. Both covered end to end by behavioural specifications, including the shell-to-microfrontend boundary.

Then it landed: if I can completely cover an existing application's behaviour with executable specs (every user flow, every edge case, every interaction), I do not need the original codebase anymore. The specs become the portable truth.

Hand those specs to AI. Say "implement this in Vue" or "implement this in React" or whatever the target stack demands. Run the specs against the output. If they pass, the implementation is correct. If they fail, the spec tells you exactly what is wrong.

The original application becomes a reference, not a dependency. The framework mismatch between legacy and target disappears. There is no line-by-line porting. No translation errors. No six-month rewrite project with a dozen engineers arguing about architecture.

The cost of this? Tokens. And the cost of tokens is in freefall.

Every enterprise I have ever worked in has at least one legacy platform nobody wants to touch. Too complex. Too risky. Too expensive to rewrite. Too critical to fail. Those platforms are not trapped by their code. They are trapped by the absence of specifications that capture what the code actually does.

Write the specs. Verify them against the running system. Once they pass, the behaviour is captured. And once the behaviour is captured, it can be reimplemented in any stack, by any team, in a fraction of the time and cost of a traditional rewrite.

The migration strategy of the future is not a rewrite. It is a specification.