What is the _opt_awcid cookie?
_opt_awcid is an HTTP cookie tied to Google Optimize, the Google platform used for A/B testing, multivariate testing, and personalizing visitor experience on a website. It is set by the Optimize script, typically loaded alongside Google Analytics or Google Tag Manager.
It appears on a site when the site owner has set up a Google Optimize experiment linked to Google Ads campaigns, in order to correlate visits with clicks originating from ads. Google announced the shutdown of Google Optimize as of September 30, 2023, so this cookie is now mostly found on sites with old, incomplete implementations.
What data it stores
The cookie typically stores an identifier tied to a Google Ads click ID (AWCID – „AdWords Click ID”), used to link the current visit to a specific advertising campaign. The exact value format is not publicly documented by Google and may vary by implementation.
The data is sent to Google domains (google.com / doubleclick.net) and to the Google Ads / Optimize account associated with the site, for reporting on experiment and campaign performance.
What it is used for
The cookie's purpose is to let Google Optimize correlate an A/B test or personalization experiment with the paid traffic source (Google Ads) that brought the visitor to the site. In practice, it helps measure how tested variants perform for visitors coming from paid ads.
For site owners, this cookie supports conversion optimization and ad budget allocation decisions by linking experiment results back to the traffic source.
Does it require consent?
_opt_awcid is classified as a marketing/tracking cookie, since it links visitor behavior to advertising campaigns. Under GDPR and Romania's Law 506/2004 (transposing the ePrivacy Directive), this type of cookie requires the visitor's explicit, prior consent before being placed.
- Site owners must list it in their cookie policy under the marketing category.
- The Google Optimize script must not load before consent is obtained.
- If a site still runs an old Google Optimize integration, it's worth reviewing and likely removing it, since the service is no longer active.
How to block or delete _opt_awcid
A visitor can delete or block this cookie through browser settings (Chrome, Firefox, Edge, Safari), via per-site cookie management, or with tracking-script blocking extensions.
For site owners, the cookie should be blocked automatically until consent is given, using a CMP such as CookieFix, which prevents the Google Optimize script (and any associated script) from loading until the visitor accepts the marketing category.
Frequently asked questions
It's a cookie set by Google Optimize, used to link A/B testing experiments to the Google Ads campaigns that brought the visitor to the site.
No, it's not a security risk, but it is a tracking/marketing cookie and must be handled under GDPR consent rules.
Google Optimize was officially discontinued in September 2023, but some sites still run old scripts that were never removed, which continue to set this cookie.
Yes, as a marketing cookie it requires the visitor's explicit consent under GDPR and Law 506/2004 before it can be placed.