Following issues with broken tracking after recently updating its cookie formats, Google has launched an official readAnalyticsStorage API, which can be used in Google Tag Manager as an official and more reliable way to retrieve client_id and session_id. Previously, people used unreliable, reverse-engineered methods to pull both IDs, as they were useful for offline conversion tracking through CRMs, for example.
The launch will allow users to pull the data officially and not be impacted by format changes in the future. GTM templates are already available on GitHub and are expected to be available in the community template area of Google Tag Manager soon.
