And that build is failing. So one of two things may be happening: 1) If this does build when you install it via Pip directly, then the difference is that Pants runs Pip in an isolated sandbox, so not all env vars are available, and you have to punch them through as @silly-queen-7197 explained. 2) If this doesn't build even directly under Pip, then you have to debug that first, and then revert to 1).