My experience with Bazel (7 years rolling it out and maintaining it in a large company) is that it provides huge value for larger teams/codebases, but at a huge

My experience with Bazel (7 years rolling it out and maintaining it in a large company) is that it provides huge value for larger teams/codebases, but at a huge cost in complexity. e.g. the three I rollouts I was closest to each took ~2 person-decades to happen; might be easier now than it was in 2016/2017, but Bazel hasn't really gotten simpler over the years Mill is intended to be much easier than Bazel. Most people would not use Bazel for a 1-person project, or even a 5-person project, and it only starts pencilling out once you have 50-100 engineers on the team. Mill in contrast works great for small projects and medium projects as well. One way I'd look at it is that Mill works great for 1-500 person projects, while Bazel works great for 100-5000 person projects. There's some overlap in the middle, but fundamentally they target different kinds of users who have very different constraints and requirements