SKAN 4.0 Overview

SKAdNetwork (SKAN) is a privacy-preserving iOS framework for mobile install attribution. SKAN 4.0, which was released in October 2022, includes the following key changes from SKAN 3.0.

  • Multiple postbacks: SKAN 4.0 sends up to 3 postbacks, a shift from 1 postback in SKAN 3.0.

  • Conversion window and postback delays: The conversion window and postback delays have become longer to ensure user privacy.

  • Postback data tier: Postback data tier is assigned to postbacks.

  • Double conversion value system: The event data is sent in fine conversion values and coarse conversion values depending on the postbacks.

Basic Principles

SKAN 4.0 operates on the following basic principles.

  • Conversion value: SKAN 4.0 sends a fine conversion value, which is a number from 0-63, and a coarse conversion value, which is a value from “low,” “medium,” and “high.”

  • Conversion window: Each postback has its own conversion window during which the user action is tracked.

    • Window 1: 0-2 days post-install

    • Window 2: 3-7 days post-install

    • Window 3: 8-35 days post-install

  • Random postback timer: All 3 postbacks have their own randomized timer, which starts 24 hours after the conversion window is closed. For example, when an app install occurs, Window 1 closes 2 days after install, and the random postback timer starts on Day 3.

SKAN 4.0 works in the following steps.

  1. SKAN 4.0 tracks the app install event by determining the attributed channel in the user’s device.

  2. The post-install events are measured, and a conversion value is determined.

  3. The conversion value is sent via postback once the random postback timer is initiated.

  4. The channel sends the conversion value to Airbridge.

  5. Airbridge decodes the conversion value into event data according to the conversion data mapping.

  6. Airbridge shows the attribution data in the dashboards.


SKAN 4.0 sends up to 3 postbacks. Depending on the user action, only 1 or 2 postbacks are sent, or all 3 postbacks are sent. To receive multiple postbacks, the following conditions must be met.

  • The iOS version of the user’s device must be 16.1 or later.

  • The Airbridge iOS SDK installed in your app must be version 1.33.1 or later.

  • The ad channel must support SKAN 4.0.

  • The postback data tier must be Tier 1, Tier 2, or Tier 3.

Conversion Window and Random Postback Timer

The conversion window and random postback timer are different for each of the 3 postbacks. All postbacks are activated following the SKAN 4.0 rules when a user installs your app and opens it for the first time.

Refer to the following image and table.

Conversion window

Random postback timer

Time of postback received

First postback

0-2 days (0-48 hours) post-install

24-48 hours after Window 1 ends

4 days (72-96 hours) post-install

Second postback

3-7 days (48-168 hours) post-install

24-144 hours after Window 2 ends

9-13 days (192-312 hours) post-install

Third postback

8-35 days (168-840 hours) post-install

24-144 hours after Window 3 ends

37-41 days (864-1,008 hours) post-install

Postback random timer

The random postback timer always starts 24 hours after a conversion window closes. For example, when Window 1 closes 48 hours post-install, the random postback timer starts 24 hours later and the postback is sent any time starting from 72 hours to 96 hours post-install.

Lock Window

The lock window is a new feature introduced in SKAN 4.0, which allows the conversion window to close when a certain conversion value is reached and start the random postback timer early. For example, when Window 2 is locked on Day 5, the random postback timer starts on Day 7. Window 3 starts on Day 8 as scheduled, regardless of the lock window being activated. Refer to the following image.

Information You Can Get From Postbacks

SKAN 4.0 offers various information: a source ID consisting of a two to four-digit number, information about app reinstallation, winning touchpoints, and the postback order. This information is sent via postbacks any time when the random postback timer is initiated.

Postback data tier

In SKAN 4.0, there are 4 postback data tiers from Tier 0 to 3, which are assigned by Apple. The more your user acquisition campaigns drive installs, the higher your tier and the more data in your postbacks. No conversion value is sent when your postback data tier is Tier 0.

No conversion value

You may receive no conversion value even if your postback data tier is 1, 2, or 3. No conversion value means that the user didn’t perform any event or performed an event that is not mapped to the conversion values and thus not measured.

Conversion value

There are two types of conversion values in SKAN 4.0. The conversion values are decoded into event data using the conversion value mapping.

Fine conversion value

The fine conversion value in SKAN 4.0 operates in the same way as the SKAN 3.0 conversion value. You can map the event data up to 64 conversion values. The fine conversion value is measured in Window 1 and sent to postback data tiers 2 or 3 only in the first postback. Use the fine conversion values to track multiple app events and event properties or to track a small number of app events and event properties in detail.

Coarse conversion value

The coarse conversion value has been newly introduced in SKAN 4.0. You can set three coarse conversion values: low, medium, and high.

In Window 1, the coarse conversion value is measured for postback data tier 1, and in Window 2 and 3, for postback data tier 1, 2, or 3. Use the coarse conversion values when tracking significant in-app events and event attributes.

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