Image: 9to5Google.

Once enabled, recommendations will begin to appear within the tab switcher, asking if you'd like to close any tabs that Chrome determines to be "stale" after an as-of-yet undetermined amount of time. You'll still need to approve any of the automated suggestions manually, so there's no need to worry about losing important tabs. Considering that this feature is still in the testing stages, there isn't much further information available regarding when to expect an official launch.

Chrome Canary (Unstable) Developer: Google LLC
Price: Free
4.3
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Source: Chromium Gerrit

Via: 9to5 Google