### 🔍 GA4 Cookie Format Has Changed: What You Need to Know About \_ga\_ and session_id
If you’ve been parsing the *ga* cookie to extract session data like session_id or client_id, Google just pulled the rug out from under you. The cookie format has changed—and if your tracking or integration logic depends on the old structure, it’s time to update.
In this post, we’ll explore: • How the old cookie format worked • What’s changed with the new format • Why direct cookie parsing is not longer safe • How to correctly retrieve session and client data using the official gtag API
### 📜 The Old Format: \_ga\_
Previously, the *ga* cookie contained **6 known structured components** packed into a single dot-separated string. Here’s a breakdown:

Example value:	`GS1.1.1690013078.2.1.1690013090.0`
Component	Meaning
`GS1`	GA4 version
`1`	Domain level
`1690013078`	Session Start Timestamp (aka `session_id`)
`2`	Session count
`1`	Engaged session (1 = yes, 0 = no)
`1690013090`	Last event timestamp
`0`	Unknown

This format was somewhat decipherable and made it possible—albeit fragile—to extract things like session_id manually by splitting the cookie on dots.
### 🔄 The New Format: GS2.1.s...\*\*
Google has quietly transitioned its Google Analytics session cookie to a new format. Now the *ga* cookie looks like this:

Example value:	`GS2.1.s1690013078$o13$g0$t1690013090$j0$l0$h2137804272`
Component	Meaning
`GS2`	GA4 version
`1`	Domain level
`s1690013078`	Session Start Timestamp (aka `session_id`)
`o2`	Session count
`g1`	Engaged session (1 = yes, 0 = no)
`t1690013090`	Last event timestamp
`j0`	Unknown
`l0`	Unknown
`h2137804272`	Unknown

In the new format, the dot-delimiter is gone and new $ -delimited key-value pairs with undocumented letter keys are introduced. The good thing is, everything that was there before still is, but in a different format and alongside new, unknown values. If your code still tries to split() this cookie expecting timestamps or session count in fixed positions, it will definitely break.

### ✅ The Recommended Fix: Use the gtag('get', ...) API
Now you would guess, the easiest way to fix your broken session_id would be to adjust your cookie split function. While this is true and valid for a quick fix, there is a better and more robust way to get things done. That’s because the only reliable and supported method to extract Google Analytics identifiers is via the official gtag.js get API! **How to get session_id and client_id:** gtag('get', 'G-XXXXXXX', 'session_id', function(sessionId) { console.log('Session ID:', sessionId); }); gtag('get', 'G-XXXXXXX', 'client_id', function(clientId) { console.log('Client ID:', clientId); }); Just replace G-XXXXXXX with your actual GA4 measurement ID and you are all set. This approach • is officially supported. • does not rely on cookies. • will continue to work across cookie format changes. • returns exactly what GA4 is using internally. You might need to take a couple of steps to leverage the new GTAG GET API for your current setup. That might feel a little challenging at first, but there’s no need to reinvent the wheel. If you are using Google Tag Manager to tag things, you can simply install Simo Ahavas GTAG GET API Template and get rid of all your cookie based Google Analytics identifiers.
### 🧾 Final Thoughts
GA4 is evolving fast, and internal structures—like the format of cookies—can and will change without notice. Relying on undocumented parsing of cookies is no longer sustainable. Using the GTAG GET API will future-proof your setup and ensure data accuracy. If you’re running custom analytics, sending data to a CRM, or integrating GA identifiers with third-party tools, now is the time to audit your implementation and remove any cookie-based parsing logic.
### Have you updated your implementation yet? We’d love to hear how you are adapting to this change–[**reach out to us to start the conversation**](/en/company/contact-us/)**.**

GA4 Cookie Format Has Changed: What You Need to Know About _ga_<MEASUREMENT_ID> and session_id

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