What's optimal for LLMs and for people is probably not going to be the same. People are a bit lazy.

Coding agents do much more than generating code though. Much of what they do relates to validating that what was generated is a valid solution. That includes everything from type checking, running tests, static code analysis, linting, running code in a headless browser, etc. The more tools agents have at their disposal, the better the feedback loop gets. But of course some of these tools are costly to run.

Statically compiled languages have a head start here as they simply exclude entire categories of bugs that a dynamically typed language might have. And with things like type inference, their token overhead can be pretty minimal. Modern languages like Kotlin or Swift are pretty compact and don't really add a lot of bloat relative to say typescript/javascript. Go is a bit more verbose but tends to work well. Rust seems pretty popular with LLM users as well. The main challenge with languages like this is the performance hit you take running their build tools. Doing that a lot slows you down and it burns a lot of tokens as well.