To coincide with an announcement of the release of Apple’s iPhone 8 (and iPhone X, according to the leaks), Apple’s new mobile operating system, iOS 11, has an official launch date of Tuesday September 12th

This update to the OS will naturally include an update to Safari, the web browser that has a market share in Europe of approximately 17% according to the research company StatCounter (closer to 25% on mobile devices).

For advertisers, one of the most important features is Intelligent Tracking Prevention, first announced by Apple’s Webkit division back in June. The update is transparently aimed at reducing the “cross-site” tracking of users for the purposes of advertising and measurement.

This new feature is designed to limit the ability for website owners and advertising platforms to track users across domains. Websites that load scripts or images from other domains will be classified using machine-learning processes, and cookies from these sites will be partitioned to prevent their use for tracking after 24 hours from the user’s original interaction.

The 24-hour exemption period from cookie partitioning is designed to enable scenarios where users may use their login information from one domain on another website or service.

After 30 days (without a subsequent interaction) the cookies will be purged completely from the user’s device. In practise this means that the cookies advertisers rely on for measurement will be unavailable after 30 days, and cookies for targeting and retargeting in media will be unavailable after 24 hours.

As always, using first-party cookies for campaign measurement and attribution will be the most robust solution.

But advertisers should be aware that even first-party cookies will be more “combustible” than they have been previously, and that the ability to measure users’ behaviour over extended periods of time could be significantly curtailed due to the 30-day time-out.

There’s some nuance to how first-party cookies will be handled by Safari moving forward, but in short, advertisers working with multi-touch attribution models may find increasingly inaccurate results for purchase journeys that last longer than 30 days.

Brands that are working with a vendor that uses proprietary technology for tracking, measurement and reporting, check with them to see whether they are expecting any deterioration in data quality as a result of ITP, and what steps they are putting in place to mitigate the risks.

Above all, it’s vital to monitor results closely over the next few weeks as the update to Safari rolls out, and avoid any rash decisions based on dramatic changes in performance data over the coming weeks.