Do Google refresh tokens expire?

This is a very confusing thread. The first answer appears to be right, but doesn't actually cite anything authoritative from google.

The most definitive answer I found is actually in the developer's playground where you obtain the token. Step 2 has a note at the bottom that says:

"Note: The OAuth Playground does not store refresh tokens, but as refresh tokens never expire, user should go to their Google Account Authorized Access page if they would like to manually revoke them."

The Google Auth server issued Refresh tokens never expire — that's the whole point of the refresh tokens. The refresh token will expire (or I should say become unauthorized) when the user revokes access to your application.

Refer this doc it clearly states the function of refresh tokens.

Instead of issuing a long lasting token (typically good for a year or unlimited lifetime), the server can issues a short-lived access token and a long lived refresh token. So in short you can use refresh tokens again and again until the user who authorized the access revokes access to your application.