Stack Selection in the Agent Era
On March 11, 2025, Anders Hejlsberg published a post titled A 10x Faster TypeScript: Microsoft was porting the TypeScript compiler to Go.
For most readers this was performance news. For me it was three old blog posts colliding. In 2021 I wrote, within the space of a few months, a piece asking whether Go was really a panacea for backend development, a piece arguing that TypeScript was indispensable for large frontend projects, and a piece praising C#'s developer experience — where I pointed out, almost as trivia, that TypeScript and C# share the same creator. Five years later, all three protagonists converged in a single repository: the compiler of the language I called indispensable, rewritten in the language I interrogated, led by the man who fathered both TypeScript and C#. I knew those articles were connected. I did not expect the connection to close like this.
The collision is worth more than nostalgia, because it exposes what has changed underneath the argument. In 2021, we debated which language was better for humans: which syntax was cleaner, which learning curve was gentler, which type system annoyed you least. The debate never ended. But the referee changed. Since then, AI coding agents have become some of the highest-frequency authors — and the very first readers — of production code. An agent does not care that Go's error handling is tedious or that TypeScript's annotations are verbose. It cares about two things: how fast it gets feedback, and whether that feedback can be trusted.
That observation is the candidate thesis of this article, stated deliberately in its modest form: when agents join the authorship of your codebase, two criteria get promoted to first class in stack selection — agent loop latency (how long one edit-to-trusted-feedback cycle takes) and the density of machine-decidable verification signals (how much of your correctness can be checked automatically, deterministically, per cycle). These criteria do not replace the human ones. They re-rank them. And under the new ranking, some of 2021's verdicts get crowned while others get overturned.
To make that case honestly, I will first excavate what we actually argued about in 2021, then define the two new criteria precisely, then examine three bodies of evidence from 2025–2026, then give the strongest counterarguments their own section, and finally propose a small selection framework you can disagree with productively.
