API authentication requirements question

Hello,

I'm trying to read public Gitlab repositories via API. However I'm faced with two issues:

Authentication question

On one hand the main API docs page states:

All API requests require authentication via a session cookie or token. 
There are three types of tokens available: private tokens, OAuth 2 tokens, and personal access tokens.

And on the other hand the API Repositories page reads:

Get a list of repository files and directories in a project. 
This endpoint can be accessed without authentication if the repository is publicly accessible.

Which one is it?

API URL

When accessing a public repo such as buble. How would the API base URL be? I can see in the docs that the endpoint would be /projects/:id/repository/tree, but I can't seem to find the whole URL in the docs, the non-endpoint of the API Request is only refered as https://gitlab.example.com/api/v4.

I tried https://api.gitlab.com/api/v4/projects/:projectid/repository/tree, but no luck. I guess I'm missing something really obvious here :/