What is VAST?
Also known as: Video Ad Serving Template, VAST 4.x
Quick definition
VAST is the IAB Tech Lab XML schema that tells a video player which ad creative to play, where its media files are and which tracking URLs to fire, making video and CTV ads portable across players and ad servers.
Key points
- Inline vs Wrapper
- Inline contains the creative; Wrapper points to another VAST URL, and long wrapper chains add latency.
- Modern companions
- VAST 4.x separates interactivity (SIMID) and verification (OM SDK / AdVerifications) from the media file, replacing VPAID.
Benefits
- Universal across web, app and CTV
- Built-in impression and quartile tracking
Trade-offs
- Wrapper chains cause timeouts and blank slots
- Measurement discrepancies between parties
FAQ
Is VPAID still used?
It is being phased out because it executed code in the player; SIMID and OM SDK cover interactivity and measurement instead.
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Official sources
Last reviewed 2026-10-27. Explanations are written by AdTech Radar; consult the official specification for implementation.