All the leading ones I've tried work mostly fine: Claude Sonnet 4.5, Opus 4.5/6/8, GPT 5.4/5, Kimi K2.5/6, GLM 5.1, and so on.

They can all write serviceable Elixir. Opus is my preferred one, but they do decently well enough for typical coding tasks.

Claude seems to work well.