IAB TCF Library Update, May 2025

Important Changes to Vendor Legitimate Interest Calculations

The IAB has announced a mandatory update to the TCF TypeScript Library (iabtcf-es) that changes how vendor legitimate interests are encoded in the TC String. This update affects all users of the IAB library, including our platform which uses this library internally.

Key Points:

• Library has been updated to version 1.5.15
• Change fixes an issue with Vendor Legitimate Interest signals
• Compliance deadline: May 2025
• No UI changes or resurfacing required

What's Changing

Vendor Legitimate Interest Signal Update

The IAB has identified an issue with how vendor legitimate interest signals were previously encoded in TC strings. As a result of this change, you will see a larger list of 'Vendor Legitimate Interests' encoded in your TC strings.

What has changed:

• Previously, vendors that declared only consent-based Purposes, but also declared Special Purposes, would not appear in the 'Vendor Legitimate Interests' portion of the TC string
• However, after this update, these "consent-only" vendors will now appear in both 'Vendor Consents' and 'Vendor Legitimate Interests' sections of the saved TCF preferences.
• In this case, since these vendors declare no purposes with legitimate interest as the legal basis for processing, the 'Vendor Legitimate Interests' signal is set to properly signal the vendor's use of legitimate interest for 'Special Purposes' only.

Example:

• For example, vendor 2 ("Captify Technologies Limited") only declares consent for several Purposes, but also declares several Special Purposes.
• In previous versions of the IAB library, vendor ID 2 would not appear in 'Vendor Legitimate Interests' erroneously, even though they declared Special Purposes.
• After this update, vendor 2 will appear in the 'Vendor Legitimate Interests' correctly, signalling that their use of Special Purposes has been communicated to the end-user.

Impact on Your Implementation

As we use the IAB library internally, we will be implementing this update before the May 2025 deadline. Here's what you need to know:

1. No user-facing changes required: We are not required to update your UI or resurface consent dialogs to your users.
2. Automatic implementation: We will handle the library update and ensure your TC strings are correctly generated.

Technical Details

For developers and technical teams, here are the specific changes:

• The issue was documented in GitHub issue #457 (opens in a new tab)
• The fix was implemented in PR #472 (opens in a new tab)

Additional Resources

• IAB TCF TypeScript Library on GitHub (opens in a new tab)
• TCF Technical Specifications (opens in a new tab)