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VAST CTV Addendum for Public Comment: Includes Backwards Compatibility for Foundational Building Blocks for CTV Success

IAB Tech Lab is releasing VAST CTV Addendum 2024 for a 30-day public comment period. The addendum provides extensions and guidance to support vital features for improved video ad delivery and measurement. It is part of a more extensive Tech Lab Advanced TV initiative to support converging technology in all TV-viewing environments, which offers the potential for new inventory, innovation, and new revenue. 

Tech Lab’s Video Ad Serving Template (VAST) is the established technical standard for the video supply chain. It is the common language for buyers and sellers to provide the required details about video ads. These details, the ad’s metadata, and links to assets have a defined structure in a VAST tag so that ad platforms can decide what to send and how to track what was served. 

VAST has “served” the market well as an effective and widely adopted standard…except that older versions of the specification still dominate the market. These older versions lack vital features for supporting Advanced TV use cases addressing the convergence of linear and connected TV environments.

VAST CTV Addendum 2024 brings the vital features of VAST 4.x to earlier versions (notably VAST 2 and 3). This addendum includes retrofitting support for: 

  • Universal ad ID for cross-media measurement 
  • Open Measurement for consistent viewability metrics across devices
  • Interactive Ads for enhanced user experience
  • Higher-resolution Mezzanine Files for versatility across platforms and devices

This addendum also includes a note about providing support for the latest macros. Though earlier versions had a list of macros encompassed within the version-specific specification document, the market’s needs require more rapid inclusion of new macros. For older versions, we’re encouraging the adoption of the macro list on GitHub updated separately from the VAST version itself.

The decision to define an addendum applicable to all versions of VAST was to support the urgent need for standardization of these critical features in the market. The explosion of streaming since 2020 has made the diligent inclusion of attributes such as UniversalAdId a requirement.  

The <UniversalAdId> field introduced in VAST 4.0 places an ID for creative assets filed with an ad registry, such as Ad-ID in the US and Pub-ID in France. A registered ID enables important ad-serving algorithms like frequency capping and competitive separation. Having a standard placement for this ID in all versions of VAST helps automate third-party identification of the ad creative and enables better ad decisioning. It also moves the ID through the supply chain for effective and efficient reporting and cross-media measurement. This effort will save the industry millions of hours (and costs!) currently spent on campaign reconciliation across linear and CTV environments.

Standardizing key features across all versions of VAST lays a foundation for improving the ecosystem of Advanced TV while lowering technical barriers to adoption. As adoption takes hold, so will innovation and growth in the TV market.

The first step is to review the draft currently available for public comment. Get it to your engineers, product managers, or anyone who works with VAST tags. Submit your feedback by May 17, 2024 to

The next step is to prepare to implement the extensions outlined in VAST CTV Addendum 2024. Coordinate with partners and prepare your teams for any new steps they may have to incorporate into their workflow. When the final addendum is released, look for any changes that might have resulted from feedback and lay out an implementation plan.
Please visit to download a copy of the draft for review.


Daniel Brackett
Chief Technology Officer and Co-Founder
XR Extreme Reach
Jarred Wilichinsky
SVP Global Digital Ad Operations