Understanding the GA4 Cookie Update: What’s New and Its Impact

4th Jul 2025

6 Minutes Read

By Akanksha Porwal

Google Analytics 4 (GA4) is designed to provide a more flexible, privacy-conscious approach to tracking user interactions across websites and apps. At the core of GA4’s tracking system are cookies, which play a crucial role in managing sessions and identifying users.

One of the primary cookies used by GA4 is _ga, which assigns a Client ID—a unique, randomly generated identifier—to each user. This Client ID is essential for distinguishing between new and returning visitors, enabling GA4 to accurately track user journeys and behaviors over time.

As GA4 continues to evolve, Google is introducing a new cookie format that changes how session information is encoded and stored. This update is designed to improve the way GA4 handles complex session data, making it more efficient and better aligned with modern privacy standards and browser restrictions.

Staying informed about these changes is critical, as they directly impact how user data is collected, processed, and interpreted in your analytics setup.

GA4 cookies:

_ga cookie: This cookie is used to distinguish unique users on domain. It stores information (a unique random number assigned to each user) to identify repeat visits and track user behavior over time.
Lifespan: 2 years

_ga cookie

_ga<container id>: This cookie manages session state data. It tracks user activity during a single visit, helping GA4 measure session duration, navigation paths, and overall engagement within that session.
Lifespan: 2 years

_ga<container id> cookie

_gid cookie: This cookie is used to distinguish the users for a short-term usage pattern.

Lifespan: 24 hrs

_gid cookie

The new GA4 cookie format, is notably different from the older version, and it's designed to be more structured and easier to interpret.

Unlike the previous format, the updated structure provides:

Clearer segmentation of data
Making it easier for developers and analysts to identify key values such as the timestamp, session ID, and user identifier.
This improvement not only simplifies debugging but also enhances transparency
It allows teams to better understand and utilize the data stored within the cookie.

Current cookie format:

We are familiar with the following cookie structure used by GA4 on the website.

Normal cookie format

GA1.1.1162820436.1749482504

Understanding about existing cookie format (_ga cookie):

Cookie Parameter	Description
GA1	It is the version detail of GA4
1	This indicates the level of the domain. eg:, "example.com" has a level of 1, while "sub.example.com" has a level of 2. This information helps us understand the structure of a website and its subdomains.
1162820436	It is the random number, this Random number generated by GA4 identifies and distinguishes the given visitor on a website.
1749482504	It is the timestamp when the cookie is created or when the user landed on the site.

New cookie format:

The new GA4 cookie structure is more organized, making it easier to identify key values like the timestamp, session ID, and user ID.

GS2.1.s1749482503$o1$g1$t1749482510$j53$l0$h1446824558

New cookie format

Understanding about new cookie format _ga_<{ID}> cookie:

Cookie Parameter	Description
GS2	This is Google stream version 2, it is the format version
1	This indicates the level of the domain
S1749482503	This represents the session ID generated at the start of a user session. The same session id is also gets recorded in the “ga_session_id” in the GA4 hits
o1	It includes session number, like 1, 2 etc
g1	It states engaged session details, eg 0 or 1
t1749482510	Last hit timestamp when cookie is created
j53	It is a joint timer
l0	It is the login state of an enhanced user
h1446824558	It states user id in hash format

Session id (S) is recorded in the ga_session_id parameter

Session number (o1) is stored in the ga_session_number parameter of GA4

Why did GA4 launch a new cookie format?

The GS2 format in GA4 is based on key-value pairs, making it significantly easier for Google to add, remove, or update fields in future without disrupting existing implementations.

This structured approach reduces ambiguity and allows developers and analysts to easily interpret each field’s purpose, without relying heavily on documentation or memorizing the position of individual values.

Does the new GA4 cookie affect the current implementation of clients?

Any custom solutions that directly parse GA4 cookies in code or use the Measurement Protocol with cookie-derived data, their data should first be validated, as these implementations may impact the current data.

It will not affect users who are using GTM or gtag.js for implementation directly.

Conclusion:

Google's introduction of GS2 cookie format marks a significant step toward the future of digital analytics. It reflects a move away from legacy tracking methods and highlights the importance of adapting to evolving data practices. With more changes likely on the horizon, it's essential to stay informed and prepared.

Overlooking these updates could result in unintentional data gaps. However, by proactively embracing these changes, you can ensure your tracking remains accurate, resilient, and aligned with privacy-focused standards.