Private Click Measurement
The system tries to find a balance between tracking users via user/device IDs with some data reports.
At the same time, we want to support measurement of online advertising. PCM achieves this tradeoff by sending attribution reports with limited data in a dedicated Private Browsing mode without any cookies, delaying reports randomly between 24 and 48 hours to disassociate events in time, and handling data on-device.
- An 8-bit identifier on the click source side, which means 256 parallel ad campaigns can be measured per website or app.
- A 4-bit identifier on the conversion side, which means 16 different conversion events can be distinguished.
- Fraud prevention via unlinkable tokens will be coming.
The WebKit post says Apple first introduced this technology in 2019 under a different name. To become a web standard, another browser needs to add PCM into its system. This is a current goal of Apple.