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Attribution & Measurement

Source Identifier (SKAdNetwork)

Also known asSource IDCampaign IdentifierSKAN Source ID

The SKAdNetwork field that identifies which ad campaign drove an install in Apple's privacy-preserving postback — formerly the 2-digit "campaign ID," now a 4-digit source identifier.

Key takeaways

  1. 01The source identifier is the SKAdNetwork field that tells an advertiser which campaign an attributed install came from.
  2. 02It replaced and expanded the original 2-digit "campaign ID" (100 values) with a 4-digit source identifier (up to 10,000 values) in SKAN 4.
  3. 03Its granularity is tied to install volume / privacy thresholds — full digits unlock only when enough conversions clear Apple's crowd-anonymity bar.
  4. 04It's the SKAN equivalent of a campaign dimension: how aggregated, privacy-safe attribution still preserves some campaign-level reporting.

The source identifier is the field in an Apple [[skadnetwork]] postback that identifies which ad campaign (or finer breakdown) drove an attributed install. It's how SKAN — which deliberately strips user-level data — still hands advertisers a campaign-level dimension to optimize against.

From campaign ID to source identifier

In early SKAdNetwork, this field was the "campaign ID": a 2-digit value allowing just 100 distinct campaigns — a severe constraint for large advertisers. SKAN 4 expanded it into the 4-digit source identifier, allowing up to 10,000 values and far more campaign/creative granularity, while keeping the framework privacy-preserving.

Granularity is gated by privacy. SKAdNetwork only reveals the finer digits of the source identifier when a campaign clears Apple's crowd-anonymity thresholds — enough installs to prevent any single user being re-identified. Low-volume campaigns receive coarser data. This is the core SKAN trade-off: campaign reporting detail scales with conversion volume, and it pairs with the [[conversion-value]] field that encodes post-install behavior.

Quick answers

What is the source identifier in SKAdNetwork?

The source identifier is the SKAdNetwork postback field that tells an advertiser which campaign drove an attributed install. It's Apple's privacy-preserving way of preserving a campaign-level reporting dimension even though SKAN removes user-level data. It was formerly called the campaign ID.

How is the source identifier different from the old campaign ID?

It's the same field, expanded. The original SKAdNetwork campaign ID was 2 digits — only 100 possible values, a hard limit for big advertisers. SKAN 4 renamed and grew it to a 4-digit source identifier supporting up to 10,000 values, giving much finer campaign and creative granularity while staying within Apple's privacy framework.

Why don't I always get the full source identifier?

Because SKAdNetwork gates granularity on crowd-anonymity thresholds. The finer digits of the source identifier (and the higher-fidelity conversion values) are only released when a campaign has enough installs that no individual user could be re-identified. High-volume campaigns get detailed reporting; low-volume ones receive coarser data.

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