gcs parameter is a parameter that is part of tracking requests sent to Google Analytics 4 as part of GA4’s Consent Mode feature.
It encodes the current state of the user’s consent.
Here’s helpling.de as an example.
Before / without consent:
After / with consent:
What it means
gcs parameter always begins with “G1” and is followed by two other digits, either 1 or 0. The G1 is a constant that indicates that the parameter is a GA4 consent mode parameter, so the first 1 doesn’t tell us anything.
The second digit indicates whether the user has given consent for the collection of personal data to be used with Google Ads. The third digit indicates whether the user has given consent for the collection of personal data to be used with Google Analytics.