VAST versions explained: 2.0 through 4.3 — and what’s next in VAST 4.4
The IAB Tech Lab has published six versions of the VAST specification, and all of them are still in active use in production. This guide covers what each version introduced, what was deprecated, and how they compare. Use this to choose the right version for your ad pipeline and validate correctly. A VAST 4.4 revision is in the works — see the VAST 4.4 preview for what to expect.
Version timeline
| Version | Released | Key addition |
|---|---|---|
| VAST 2.0 | 2008 | Foundation: inline, wrapper, tracking, companions |
| VAST 3.0 | 2012 | Skippable ads, industry icons, Ad Pods |
| VAST 4.0 | 2016 | Server-side ad insertion (SSAI), mezzanine files, UniversalAdId |
| VAST 4.1 | 2018 | OMID verification, interactive files, closed captions |
| VAST 4.2 | 2019 | Macro enhancements, conditional ad improvements |
| VAST 4.3 | Dec 2022 | SIMID formalized, VPAID fully removed, CTV measurement |
| VAST CTV Addendum 2024 | Jul 2024 | ACIF, DSA icons, high-res creative (backwards-compatible extensions) |
| VAST 4.4 | Expected | ACIF native integration, DSA compliance, macro updates — preview → |
VAST 2.0: the foundation
VAST 2.0 is the baseline. It introduced the core structure that every later version builds on: inline ads, wrapper chains, impression tracking, companion ads, and media files with delivery and codec attributes. Most legacy ad servers and many DSPs still emit 2.0 tags.
Key elements:
<InLine>and<Wrapper><Impression>,<Tracking>,<ClickThrough><MediaFile>withdelivery,type,width,height<CompanionAds>
VAST 3.0: skippable ads and Ad Pods
VAST 3.0 added support for skippable linear ads (via skipoffset), the Ad Pod sequence for mid-roll ad breaks, industry icon overlays, and VPAID integration for interactive creatives.
New in 3.0:
skipoffsetattribute on<Linear><AdPod>sequencing for ad break scheduling<Icons>for AdChoices and similar overlaysapiFramework="VPAID"on<MediaFile><AdParameters>for passing data to interactive creatives
VAST 4.0: SSAI and mezzanine files
VAST 4.0 was a major revision targeting server-side ad insertion (SSAI) and CTV. It introduced mezzanine files (high-quality source for server-side transcoding), <UniversalAdId> for cross-platform ad deduplication, and deprecated VPAID in favor of more structured approaches.
New in 4.0:
<Mezzanine>/<MediaFile>withfileSize<UniversalAdId>: unique ad identification across systems<Category>for content categorization<ViewableImpression>for viewability tracking- VPAID officially discouraged (beginning of deprecation)
VAST 4.1: OMID and interactive files
VAST 4.1 introduced the <Verification> element (part of the OMID framework) for third-party measurement, <InteractiveCreativeFile> for SIMID-based interactivity, and <ClosedCaptionFiles> for accessibility.
New in 4.1:
<AdVerifications>→<Verification>(OMID)<InteractiveCreativeFile><ClosedCaptionFiles>- Refined error codes and reporting
VAST 4.2: macros and conditional ads
VAST 4.2 was a maintenance release with improvements to macro handling, conditional ad support, and measurement standards. It clarified the behavior of several elements and added explicit macro-replacement rules.
VAST 4.3: SIMID formalized and VPAID fully removed
VAST 4.3 (December 2022) is the current released version. It made three significant changes:
- SIMID formalized — SIMID 1.0–1.2 becomes the official mechanism for interactive creatives via
<InteractiveCreativeFile apiFramework="SIMID">. Interactive nonlinear ads use<IFrameResource>inside<NonLinearAds>. - VPAID fully removed — After deprecation in 4.0 and discouragement in 4.1–4.2,
apiFramework="VPAID"is invalid in a 4.3 document. vastlint flags it as an error. See the VPAID migration guide. - Improved CTV measurement — Better impression reconciliation and viewability tracking for server-side insertion environments. Refinements to
<ViewableImpression>semantics and wrapper chain handling.
The VAST CTV Addendum 2024 (July 2024) followed as a separate document, adding backwards-compatible extensions for ACIF ad registration, DSA compliance icons, and high-resolution creative support across all VAST versions. These extensions are the most likely candidates for native incorporation in VAST 4.4. Read the VAST 4.4 preview →
Which VAST version should I use?
- VAST 4.2 or 4.3: recommended for new implementations. Full feature set, OMID verification, UniversalAdId, no VPAID dependency.
- VAST 3.0: still common in the long tail. If you're accepting third-party tags, expect to encounter 3.0 frequently.
- VAST 2.0: legacy. Still emitted by older ad servers. Accept it as input but don't generate it for new campaigns.
vastlint detects the version automatically from the version attribute and validates against the correct spec. Elements that are invalid for the declared version are flagged, for example using <UniversalAdId> in a VAST 3.0 document.
Version compatibility matrix
| Feature | 2.0 | 3.0 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 (expected) |
|---|---|---|---|---|---|---|---|
| Inline / Wrapper | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Skippable ads | — | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| VPAID | — | ✓ | ⚠ Deprecated | ⚠ | ⚠ | ✗ Removed | ✗ |
| UniversalAdId | — | — | ✓ | ✓ | ✓ | ✓ | ✓ |
| OMID Verification | — | — | — | ✓ | ✓ | ✓ | ✓ |
| Mezzanine files | — | — | ✓ | ✓ | ✓ | ✓ | ✓ |
| SIMID | — | — | — | — | — | ✓ | ✓ |
| Closed captions | — | — | — | ✓ | ✓ | ✓ | ✓ |
| ACIF (ad creative ID) | — | — | — | — | — | ext | ✓ (expected) |
| DSA icon compliance | — | — | — | — | — | ext | ✓ (expected) |
ext = supported via VAST CTV Addendum 2024 extension; ✓ = native in spec; ⚠ = deprecated; ✗ = removed.
Validate across all versions
vastlint validates VAST 2.0 through 4.3 with version-aware rules. Paste a tag into the web validator to see exactly which rules fire for your declared version.