A founder shares lessons from building 150,000 lines of production Elixir entirely with AI (Claude Code). Elixir's small, terse, immutable nature makes it well-suited for AI coding agents—fewer decisions, fewer tokens, fewer hallucinations. The Tidewave MCP tool extends agent capabilities with live logs and DB access. Key downsides: AI defaults to imperative, defensive Ruby-style code rather than idiomatic Elixir; it cannot debug OTP/async issues or understand Ecto sandbox transaction isolation, causing it to chase red herrings in tests. Architecture decisions still require human oversight. Despite the friction, productivity gains are described as massive.
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