In some environments it's traditional to commit third-party code into the repository, but you usually don't want to review changes to them. Reviewable will now recognize these so-called "vendored" files, put them into a new group that's collapsed by default, and exclude them from file rename matching (to reduce PR analysis time).
We have some basic heuristics for automatically detecting vendored files based on path but please let us know if we should add new rules for your favorite language! You can also take manual control of the process and mark files as vendored or not in your custom completion condition.
Here's to more meaningful reviews!