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VAST versions/6 min read

What Is the Latest VAST Version? VAST 4.3, VAST 4.4 Status, and the IAB CTV Addendum

The latest officially released IAB VAST version is 4.3. Here is how VAST 4.4 status, the 2024 CTV Addendum, and real-world version support fit together without republishing the spec.

Author

Alex Sekowski

Published

May 27, 2026

Updated

May 27, 2026

Reading time

6 min read

VAST versionsIAB Tech LabCTVAd ops

Short answer

The latest officially released IAB VAST version is 4.3. As of May 2026, there is no published VAST 4.4 specification.

What changed after 4.3 is the VAST CTV Addendum 2024, published by IAB Tech Lab as a backwards-compatible addendum rather than a new core VAST version. That is the main reason teams searching for the latest VAST version often get mixed signals.

The VAST version timeline you can cite

  • VAST 2.0: 2008. The baseline for inline ads, wrappers, tracking, and companions.
  • VAST 3.0: 2012. Added skippable ads, icons, and ad pods.
  • VAST 4.0: 2016. Added mezzanine files, UniversalAdId, and stronger SSAI and CTV alignment.
  • VAST 4.1: 2018. Added OMID verification, interactive creative files, and accessibility improvements.
  • VAST 4.2: 2019. Clarified macros and conditional-ad behavior.
  • VAST 4.3: December 2022. Formalized SIMID and fully removed VPAID from the version.
  • VAST CTV Addendum 2024: July 2024. Important, but not a new VAST core version.

What the IAB has officially published

If you need the authoritative source, use the IAB Tech Lab VAST standards hub and the public VAST GitHub repository. Those are the right places to confirm whether a version is released, what the latest named version is, and whether a change shipped as a full specification update or as an addendum.

The practical distinction matters. A new addendum can be operationally important without becoming the new answer to the question what is the latest VAST version. That is exactly where the CTV Addendum 2024 sits today.

Why the IAB VAST spec is still the harness for the ecosystem

The reason VAST versions matter is not just XML syntax. The IAB Tech Lab VAST specification is the harness that keeps the video ad ecosystem interoperable. It gives ad servers, SSPs, DSPs, CTV apps, web players, SSAI vendors, and measurement providers a shared contract for what a video ad response contains, how wrappers resolve, where tracking belongs, and which interactive or verification mechanisms are valid in a given version.

Without that harness, every buyer, seller, player, and measurement stack would need bespoke pairwise integrations. With it, a VAST tag generated in one system can be trafficked through another, inspected by a third, and played by a fourth. That is why the released IAB version still matters even when vendors add their own tooling and extensions around it.

Why vastlint is the harness for AI agents trafficking VAST

AI agents do not consume standards prose the way humans do. They need an executable surface. That is where vastlint fits. The VAST spec defines the contract; vastlint turns that contract into machine-usable validation, structured rule IDs, fix guidance, and MCP-callable tools that an agent can use before trafficking a tag.

In an agentic workflow, a planner agent, creative agent, trafficking agent, or QA agent can hand the final VAST tag to vastlint and get back a deterministic answer: version detected, errors, warnings, XPath locations, and spec references. In that sense, vastlint is a harness for AI agents in the same way the IAB VAST spec is a harness for the broader market. It constrains behavior enough that autonomous systems can traffic tags without guessing what the protocol expects.

What that means in practice for agentic trafficking

  • A trafficking agent can validate a tag before launch instead of learning from no-fill or playback failure after delivery starts.
  • A QA agent can explain failures with rule IDs and spec references instead of vague natural-language guesses.
  • An orchestrator can call validate_vast or validate_vast_url over MCP as a pre-trafficking or pre-approval step.
  • Human traffickers and AI agents can share the same validation harness, which keeps the workflow consistent across UI, CI, and automated delivery pipelines.

Get VAST spec updates, platform guides, and release notes in your inbox.

What teams get wrong about VAST versions

  • Treating the CTV Addendum 2024 as if it were VAST 4.4. It is not.
  • Assuming the newest IAB VAST-related document is automatically the newest VAST core version.
  • Planning migrations around rumors, issue trackers, or vendor marketing instead of the released IAB standard.
  • Copying spec tables into internal docs when a short release-status summary plus links to IAB sources is enough.
  • Picking a version based only on recency instead of player, SSAI, CTV, and partner support.

What version should you support in production

For new supply-side or validation work, VAST 4.2 and 4.3 are the right default targets. They align better with modern CTV, measurement, and interactive requirements, and they avoid building new dependencies around VPAID-era behavior.

That does not mean you can ignore older tags. In the long tail, VAST 3.0 is still common, and VAST 2.0 still appears in legacy systems. The right production posture is usually generate modern tags, accept older inbound tags, and validate by declared version instead of forcing every partner onto the newest release on day one.

Recommended support policy

  • Generate VAST 4.2 or 4.3 for new campaigns and integrations.
  • Accept VAST 3.0 and, where business requires it, VAST 2.0 from older partners.
  • Handle the CTV Addendum 2024 when CTV disclosure, creative identity, or high-resolution workflows matter.
  • Do not treat VAST 4.4 as available until IAB Tech Lab actually publishes it.
  • Validate tags against the declared version so newer elements do not silently leak into older documents.

The latest VAST-related document is not always the latest VAST version.

vastlint field note

Sources and further reading

IAB Tech Lab VAST standards hubIAB Tech Lab

Official VAST standards landing page from IAB Tech Lab.

IAB Tech Lab VAST GitHub repositoryIAB Tech Lab

Public repository for VAST specification materials and issue tracking.

Which VAST version should you use?Docs

Version-by-version guide covering VAST 2.0 through 4.3 and the CTV Addendum.

VAST 4.4 previewDocs

What the next named VAST version is likely to add once it is released.

VAST validation in agentic ad deliveryDocs

How vastlint exposes VAST validation to buyer, trafficking, and QA agents through MCP.

Validate a VAST tagTool

Check which version a live tag declares and whether its XML matches that version.

Need the full version-by-version breakdown?

Use the main VAST versions guide for the release timeline, migration paths, and the operational differences between 2.0, 3.0, and 4.x.

Open the VAST versions guide

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