VPAID and SIMID together lines up two runtimes and no fallback

VPAID and SIMID together is the compatibility idea that survives deprecation memos. The tag lists a VPAID media file for old web players and a SIMID interactive file for everyone else. IAB's SIMID page does not describe that pair as a fallback chain. It says VPAID is being replaced, OMID takes measurement, SIMID takes interactivity, and the interactive layer is separate from the media asset so the player keeps the stream. The asset is a media file. VPAID was allowed to be that asset. SIMID is not allowed to be that asset.

A player that implements SIMID and finds no media file does not owe you a VPAID session as consolation. A player that only implements VPAID does not open the SIMID sidecar. You have two products in one response, and each audience misses one of them. vastlint checks both apiFramework values in a VAST 2.0–4.4 inline, and whether a non-executable file remains. It does not execute VPAID and it does not open a SIMID session. Seeing both strings is not a pass.

The together that matches the standards

Media file, always, if you want the ad to play when interaction is skipped. SIMID, only when there is an interaction, as InteractiveCreativeFile with type text/html. OMID, only when a vendor must measure, in AdVerifications. That trio is the replacement. VPAID is absent from it. If a named HTML5 seat still requires VPAID, that is a separate tag or a documented exception, not a silent sibling on the CTV copy.

Google publishes the two as separate HTML5 documents: VPAID 2 limited to the HTML5 SDK, and SIMID support with its own list of messages. A player can implement a subset of SIMID and none of VPAID. Counting on both to be present because both were in the XML overstates what either document promised.

Wrappers make the double declaration look like one creative

Hop one can be a plain wrapper. The inline can carry VPAID as the media file and SIMID as a URL that 404s, or the reverse. QA that stops on the wrapper blesses the campaign. The player that unwraps finds out which half is real. Inspect the chain, then validate the inline you would actually serve.

Measurement does not get to hide inside whichever half runs. If the VPAID unit used to carry the viewability script, moving that script into the SIMID file repeats the bundle. Put it in the verification node so it does not depend on which framework the player chose to ignore.

If both strings are in the inline

• Confirm a decodable media file exists that is neither framework.
• Treat the VPAID file as legacy HTML5, not as the spare for SIMID.
• Treat SIMID as optional interaction, not as the media.
• Keep OMID in AdVerifications.
• Do not read a structural pass as proof that both runtimes executed.