How SKAN 4.0 Works (Simple Explanation for 2025)

SKAN 4.0 is Apple's latest version of SKAdNetwork, released in 2022 but seeing widespread adoption throughout 2024-2025.

The biggest change: you now get up to three postbacks per install instead of one, extending measurement from 2 days to 35 days post-install.

Here's what actually changed and what it means for your iOS campaigns.

What's New in SKAN 4.0

1. Multiple Postbacks

SKAN 3.0 sent one postback covering 24-72 hours after install. SKAN 4.0 sends up to three:

Postback 1 (0-2 days): Fine-grained conversion value (0-63) and coarse value (low/medium/high)

Postback 2 (3-7 days): Coarse conversion value only

Postback 3 (8-35 days): Coarse conversion value only

Each postback arrives after its window closes, plus Apple's random delay (0-24 hours).

This means you can measure user behavior across a full month, not just the first 48 hours.

2. Coarse Conversion Values

SKAN 4.0 introduced a second type of conversion value with only three tiers:

• Low
• Medium
• High

You define what these mean. Common approaches:

• Map to revenue ranges (low = $0-1, medium = $1-5, high = $5+)
• Map to retention (low = 1 session, medium = 2-3 sessions, high = 4+ sessions)
• Map to key events (low = install only, medium = tutorial complete, high = purchase)

Coarse values appear in all three postbacks. Fine values (0-63) only appear in the first postback.

3. Expanded Source Identifier

Campaign IDs expanded from 2 digits (0-99) to 4 digits (0-9,999).

This lets you:

• Test more campaign variations simultaneously
• Separate campaigns by geo, creative type, or audience without running out of IDs
• Structure campaigns with more granular reporting

The increased capacity matters most for large advertisers running hundreds of concurrent campaigns.

4. Web-to-App Attribution

SKAN 4.0 measures installs that originate from Safari web ads.

This is significant because 93.65% of iPhone users use Safari as their default browser. Previously, web-driven installs were largely invisible to SKAN.

The process:

1. User clicks an ad in mobile Safari
2. Apple registers the click with SKAdNetwork
3. User installs the app from the App Store
4. Attribution flows through SKAN like an in-app install

Web-to-app attribution works the same way as in-app attribution, including the same privacy mechanisms and postback structure.

5. Crowd Anonymity Tiers

Apple expanded privacy thresholds into four tiers (0, 1, 2, 3).

Each install gets assigned to a tier based on how many other users from the same campaign installed around the same time.

Higher tier = more data.

Lower tier = fields get dropped to preserve privacy.

Fields that can be removed at lower tiers:

• Fine-grained conversion value
• Coarse-grained conversion value
• Source ID
• Source app ID

In practice, this means low-volume campaigns receive less granular data. You need sufficient scale for SKAN to provide full attribution details.

How the Postback Windows Work

Each postback measures a specific time window:

Window 1 (0-2 days):

• Measures immediate post-install behavior
• Best for: Tutorial completion, first session events, initial engagement
• Includes both fine (0-63) and coarse (low/medium/high) values
• Arrives 2-3 days after install

Window 2 (3-7 days):

• Measures short-term retention and engagement
• Best for: D3-D7 retention, subscription trials, early purchases
• Includes only coarse values
• Arrives 7-8 days after install

Window 3 (8-35 days):

• Measures longer-term value
• Best for: Subscription conversions, payback periods, D30 retention
• Includes only coarse values
• Arrives 35-36 days after install

The conversion value in each window is independent. You can track different events in each window.

Setting Up Conversion Value Schemas

Your MMP handles the technical setup, but you define the strategy.

For fine values (window 1):

You have 64 possible values (0-63) to encode user behavior. Common approaches:

• Revenue-based: Map dollar ranges to values (0 = $0, 1 = $0.01-1.00, 2 = $1.01-2.00, etc.)
• Event-based: Assign values to key events (5 = tutorial complete, 10 = level 3 complete, 15 = first purchase)
• Hybrid: Combine revenue and events into a single encoding scheme

For coarse values (all three windows):

Define what constitutes low, medium, and high for each window:

• Window 1: Session count (low = 1, medium = 2-3, high = 4+)
• Window 2: Retention (low = no return, medium = 1-2 sessions, high = 3+ sessions)
• Window 3: Revenue (low = $0, medium = $1-10, high = $10+)

The strategy depends on your monetization model and what metrics matter for optimization.

Practical Impact on Campaign Management

SKAN 4.0 changed how iOS campaigns operate:

Longer optimization window: You can now optimize based on 7-day or 35-day behavior, not just 48-hour activity.

Better value prediction: Multiple postbacks let you identify high-value users earlier and optimize toward them.

More complex setup: Three postback windows mean more schema configuration and more data to analyze.

Slower feedback loops: If you optimize based on window 3 data, you're working with 35+ day delays.

Migration from SKAN 3.0

As of 2025, the industry is in transition:

• Most major ad networks support both SKAN 3.0 and 4.0
• Meta began pushing broad SKAN 4.0 activation in mid-2025
• Many advertisers still use SKAN 3.0 schemas

Migration requires:

1. Updating your MMP configuration
2. Setting up new conversion value schemas for all three windows
3. Coordinating with ad networks to ensure they're sending SKAN 4.0 postbacks
4. Testing to verify data flows correctly

The migration isn't automatic. It requires manual configuration in most platforms.

Current Adoption (2025)

SKAN 4.0 adoption accelerated significantly in 2025:

• Meta activated SKAN 4.0 across advertising accounts
• TikTok, Google, and other major networks support SKAN 4.0
• Most MMPs (AppsFlyer, Adjust, Singular) provide full SKAN 4.0 functionality

However, advertisers must manually configure their setup. Auto-migration hasn't happened for most apps.

FAQs

What's new in SKAN 4.0?

SKAN 4.0 introduced multiple postbacks (up to 3 per install), web-to-app attribution for Safari, expanded campaign IDs (up to 10,000 values), and coarse conversion values alongside fine-grained values.

How many postbacks does SKAN 4.0 provide?

SKAN 4.0 provides up to 3 postbacks per install, covering windows of 0-2 days, 3-7 days, and 8-35 days post-install. Only the first postback includes fine-grained conversion values.

What are coarse conversion values in SKAN 4.0?

Coarse conversion values are simplified metrics with only three possible values: low, medium, or high. They're used in postbacks 2 and 3, and in situations where crowd anonymity requirements limit data granularity.

Do I need to migrate from SKAN 3.0 to SKAN 4.0?

Not immediately, but it's recommended. SKAN 4.0 provides significantly better measurement (35 days vs. 2 days) and most major ad networks now support it. Migration requires manual configuration through your MMP.

Can I use both fine and coarse values in the first postback?

Yes. The first postback (0-2 days) includes both a fine-grained value (0-63) and a coarse value (low/medium/high). The second and third postbacks include only coarse values.

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SKAN 4.0 represents a meaningful improvement over SKAN 3.0, particularly for apps with longer monetization cycles. The added measurement windows and web attribution capabilities make iOS campaigns more measurable, even within Apple's privacy constraints.