Cross-domain tracking in Google Analytics 4 (GA4) ensures accurate user journey measurement across multiple websites by preserving session and client identifiers as visitors move between domains. Without this setup, GA4 treats each domain visit as a separate session, inflating user counts and distorting conversion data. The process requires configuring a shared GA4 property across all domains and specifying the included domains in the Admin interface. While subdomains are automatically tracked, separate domains (like example.com and partner.com) need explicit cross-domain measurement to maintain data continuity.

Key requirements for successful implementation:

• All domains must use the same GA4 Measurement ID (cross-domain tracking cannot work with separate GA accounts) ^[1][4][6]
• Configuration is done through GA4 Admin > Data Streams > Configure Tag Settings ^[1][7][10]
• Testing is critical to verify the _gl URL parameter appears on cross-domain links ^[5][10]
• Subdomains (e.g., shop.example.com) do not require cross-domain tracking ^[1][3][10]

Setting Up Google Analytics 4 Cross-Domain Tracking

Prerequisites and Core Requirements

Before configuring cross-domain tracking, ensure your setup meets GA4’s technical requirements. The most critical prerequisite is using a single GA4 property across all domains, as cross-domain tracking cannot bridge separate GA accounts or Measurement IDs. This limitation is explicitly confirmed by Google’s support documentation and community discussions ^[4][6]. For example, tracking users from a Japanese domain (jp.example.com) to an English domain (en.example.com) requires both sites to share the same GA4 property; otherwise, cross-domain data will be lost ^[4].

Additional prerequisites include:

• Google Tag Manager (GTM) or gtag.js implementation: While GA4’s Admin interface simplifies setup, GTM is recommended for advanced configurations ^[5][7]
• Editor-level access to the GA4 property to modify data streams and domain settings ^[9]
• List of all domains to be tracked, including variations (e.g., example.com and www.example.com) ^[7]
• Consent for cookie tracking where legally required (e.g., GDPR compliance) ^[9]

A common misconception is that cross-domain tracking can work with separate GA accounts. Multiple sources explicitly state this is impossible: "Cross-domain tracking typically requires the same GA4 property across both domains" ^[4], and attempts to track across different Measurement IDs will result in users being recorded as referrals rather than continuous sessions ^[6]. For businesses requiring separate analytics accounts (e.g., regional teams), alternative solutions like UTM parameters or API-based data merging must be explored, though these won’t provide true cross-domain session continuity.

Step-by-Step Configuration Process

The setup process for GA4 cross-domain tracking is centralized in the Admin interface, eliminating the need for manual code changes in most cases. Below is the validated sequence based on consensus across all sources:

1. Access the GA4 Admin Panel

Navigate to analytics.google.com, select your property, and click Admin (gear icon in the lower-left corner). Under the Property column, select Data Streams ^[1][7][10].

1. Configure Tag Settings - Select the web data stream associated with your primary domain. - Click Configure Tag Settings (or "Tagging Settings" in some interfaces) ^[1][8]. - Choose Configure Your Domains (or "Cross-Domain Measurement" in older GA4 versions) ^[7][9].

1. Add Domains for Tracking - In the Domains field, enter all domains to include in cross-domain tracking, separated by commas. Examples: - example.com,partner.com,checkout.example.com - Ensure no spaces between domains ^[7][10]. - Exclude subdomains unless they are distinct properties (e.g., blog.example.com is automatically tracked if example.com is listed) ^[1][3]. - Click Save to apply changes.

1. Verify the Setup - Test the _gl parameter: After configuration, click a cross-domain link (e.g., from example.com to partner.com). The destination URL should include a _gl parameter (e.g., partner.com/?_gl=1abc123) ^[5][10]. - Use DebugView: In GA4, enable DebugView (under Admin > DebugView) to confirm cross-domain hits appear as a single session ^[10]. - Check Real-Time Reports: Navigate between domains while monitoring the Real-Time report to ensure user continuity ^[7].

Troubleshooting Common Issues:

• Missing _gl parameter: Ensure the GA4 tag is firing on both domains and no ad blockers are interfering ^[5].
• Session breaks: Verify all domains are listed in the Configure Your Domains field without typos ^[7].
• Data discrepancies: Cross-domain tracking does not retroactively fix historical data; only new sessions will be unified ^[9].

For advanced setups (e.g., dynamic domains or non-HTML environments), manual configuration via gtag.js or Google Tag Manager may be required. This involves creating a linker object to pass client IDs between domains, as documented in Google’s developer guides ^[2]. However, the Admin interface method is sufficient for 90% of use cases ^[5].