Does OAuth2.0 authenticate every request?

I have a project that leverages googles OAuth servers for authentication but I’m confused how the user stays authenticated throughout the session. It doesn’t seem like my resource server interacts with googles auth server for every request just the initial login authorization. I noticed that there is an access token of some sort sent to my resource server upon a successful authentication with an expiration but it’s not saved anywhere or at least I’m not saving it manually, just the principal. So basically, is every request being authenticated or is oauth just for the initial login?