Google recently made changes to create the new GA4 cookie, which has a format change from the old setup. How could this impact online marketing?

The newly updated cookies track much more information than before and do so using a new method. Instead of a simple dot-separated strong, it now has a complex, labeled format. The change was unannounced by Google and broke many tracking and analytics implementations that assumed cookies were going to continue to use the old structure. This has impacts in many sectors, including marketing, web analytics, and data sorting.

Let’s take a look at the new GA4 cookie format change and what you should be aware of going forward.

What changed about this new format?

Computer programming is extremely specific and reliant upon languages and recognition of various information that’s universally known and understood. In the previous format for sessions, cookies used dots to separate the numerical indicators. This new format changed to using dollar signs for these separations while also updating from GA1.1 to GS2.1 as the prefix.

Every piece of data in the cookie is self-describing, using the letter prefix, which can be found directly after the dollar sign separators in the cookies. The new GA4 cookie format changed from a positional numeric format to a key=value style format using labeled parameters.

Why did Google make this change?

A change to something as important and widely used as tracking cookies requires thought, research, and several reasons to make the change. Of course, it would have been nice if Google had provided guidance and a warning instead of making the change overnight and in silence.

Some of the reasons for the format change are:

• Improved extensibility
• Self-documenting structure
• Version control
• Data optimization
• Handles errors better
• Modern format

Trouble caused overnight

The new GA4 cookie format change is a prime example of why Google and other search engines need to provide information and announce changes before they happen. This silent change caused systems that rely on the cookie’s format to break without any warning.

Some of what happened because of this change included:

• Custom JavaScript stopped extracting the right IDs when parsing cookies
• Google Tag Managerbegan misfiring for setups by sending incomplete data
• Measurement Protocol eventscould have invalid or missing client/session IDs
• CRM and CDP integrationscould fail to link user behavior
• Attribution toolsmight start miscounting users and sessions

Basically, most systems that relied on the old cookie format to provide accurate information suddenly weren’t able to deliver the desired information to companies that required it for reporting. These failures are as silent as the update, resulting in tags with wrong information, marketing and analytics issues, and flawed information for engineers.

What should you do to address this issue now?

There are some important steps that need to be taken to ensure your programming is accepting of the new cookie format, giving you the updated information that will help ensure your reports and analytics continue to offer the accuracy that you rely on to do your job.

The most important steps to take immediately are:

• Audit your tracking stack– Check your website, tag manager, or data layer to ensure it parses GA cookies directly. If you see programming with .split(‘.’), you’ve got a problem and need to update your information
• Patch parsing logic– Create custom code to handle both the old and new cookie formats. Wherever you can, utilize Google’s official API methods
• Test key journeys– Verify the information, such as returning users that are stitched correctly, conversions are attributed, and sessions aren’t being duplicated
• Annotate your reports– Go back to the end of May 2025 and begin flagging reports with numbers that don’t look normal. The new cookie format could be why
• Communicate with your team– Let your leadership and those who utilize online-generated reports know about the issue and what’s happening to fix the problem

Get with the changes

Google is the top search engine utilized online around the world. This change should have been announced, but it’s here and there’s nothing you can do about it. The new GA4 cookie format change shows that the GS2 cookie is a signal that Google is future proofing its analytics infrastructure. We’ve known for a while that parsing cookies were coming to an end and this is a signal toward that change.

Your data strategies must change and adapt with the times, and this new forma makes data more resilient to information hacking. Take the necessary measures to embrace the new GA4 cookie format change and allow your data to be accurate and take advantage of the new cookie format.