Apple's WebKit (Safari) continues its aggressive approach to cookie expiration, now on server set cookies
TL:DR Unless you've been using a server to extend cookie expiration, the Safari 16.4 updates will not impact you. If you have been using server set cookies, then Safari 16.4 will only impact you if the IP address of the server that's extending the cookie is materially different than the IP address of the server your site is loaded from.
Think of cookies as little storage devices, used for several functions in the browser, like saving your shopping cart, your language settings, your privacy settings etc... Not surprisingly, cookies are also used to save marketing information. When you click on an add, typically, the information about the add you clicked on is saved in a cookie, that saved cookie is then used to link the add click to an event like a purchase. If that cookie is unavailable at the time of purchase, the add click won't be connected with the purchase, and the purchase will go unattributed in whichever ad platforms you might be using. Google Ads Conversion 0. Apple 1.
Cookies have expiry dates. These expiry dates depend on a number of factors. The longer the expiry, the better for tracking purposes. The longer we have the marketing information, the longer we are able to connect the ad click to the actions users take on your site. With a 1 day expiry (which is the standard in Safari for ad clicks) If a user comes to your site via an ad click at 9AM Monday morning, and returns to make their purchase Tuesday at 10AM, the purchase will not be linked to the ad click.
Before Safari 16.4, one work around for extending cookies is using something called a server set cookie. By setting the cookie from the server the cookie typically has a 1 year expiry (vs. 7 days or 1 day in Safari/WebKit browsers). As of today, with the release of 16.4, this method of extending cookie expiry will only work if the server that attempts to do the extension, is not materially different in IP address than the address of the server your page is loaded from. You can learn more about the details of these changes in Simo Ahava's LinkedIn post here and by listening to a recent podcast by Elevar founder Brad Redding here.
In short, if you aren't extending cookies from a server, Safari 16.4 should have no impact on your tracking.
Updated 1 day ago