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IAB Tech Lab Releases Final Version of VAST 4.1

By Amit Shetty

The Digital Video Ad Serving Template Version 4.1 (VAST 4.1) was released for public comment on June 14th 2018, and received an unprecedented amount of feedback, reflecting the level of interest in this release of VAST. Following discussions in the Digital Video Working Group, we are now releasing the final VAST 4.1 specs available here.

Will the real VAST 4 please stand up?

As a reminder, VAST 4.1 is the latest version of VAST 4. The IAB Tech Lab & the Digital Video Working group see VAST 4.1 as the “real” VAST 4 because the first release (VAST 4.0) had a major gap that prevented it from being fully adopted – the lack of direction for how verification should work in a world where the MediaFile node has to be separated from any executable code. That has been addressed in VAST 4.1, along with the release of Open Measurement.

There are a number of additional features beyond verification in VAST 4.1, and they are listed on page 8 of the specs.

In the interest of transparency, the following changes have been made to the VAST 4.1 specs (compared to the public comment version):

  1. Nonlinear ads are no longer deprecated. We received feedback that there were people still using them, and we have decided to investigate their use cases in further detail and to determine whether those use cases can be supported via other paths. (Note – we would like to solicitate further feedback on this topic from people using Nonlinear ads).
  2. Added a “notUsed” tracking event to be used to support scenarios where an ad may not get used.
  3. Some more fixes were made to the AdVerifications
  4. Did a lot of cleanup on the “human readable” section (note that when in doubt, always go to section 3)
  5. Updated to Macros to improve ad request context (OMIDPARTNER, INVENTORYSTATE, CONTENTID)
  6. And a number of minor fixes (missing attributes, fixes to the human readable section, etc.) were made throughout the document.



What’s next?

As discussed in the video vision blog post, the Video Suite (VSUITE) is undergoing a complete refresh.  Now that we have updated VAST, and delivered a replacement for VPAID (Video Player Ad-Serving Interface Definition) focused on measurement/verification (Open Measurement), the Digital Video Technical Working Group is working on a replacement for VPAID for interactivity features. This might result in some minor updates to VAST and will be delivered as VAST 4.2, but that should not stop anyone from implementing VAST 4.1. We will ensure that 4.2 is additive as well as backwards compatible, so that 4.1 implementations are not broken.

More to come!

While the VAST 4.1 specs provide context around the various updates, we want to bring focused attention to the main updates. To that end, some of our members are working on a series of blog posts to highlight each major area that changed in VAST 4.1. Please come visit the blog section (or come back to this page) over the course of the next few weeks as we publish the following blog posts:

  1. Expand verification with VAST 4.1 & Open Measurement
  2. VAST 4.1 – now with Audio powers!
  3. Cleaning up interactive ads with VAST Interactive Templates
  4. Upgrading Video Ad Delivery Workflows with VAST 4.1
  5. Moving to VAST 4.1 from VAST 2.0 or VAST 3.0 – not as scary as it seems.

In addition, please join us at the IAB Tech Lab Video Summit on December 12th 2018 in NYC. We will be covering these updates and a lot more at this inaugural IAB Tech Lab event!

VAST 4.1 resources:

The IAB Tech Lab also has some resources to help the move to VAST 4.1.

  1. Sample xml :
  2. VAST 4.1 XSD :
  3. VAST tag validator –

We also welcome contributions to these tools, so feel free to contribute your samples!


Amit Shetty
Senior Director, Video & Audio Products