Thanks for the question, @meghan_nanigans.
GIFs are not supported for video website cards. If you try to use a GIF in create through the Ads API, you’ll see the following error:
$ twurl -X POST -H ads-api.twitter.com "/3/accounts/18ce54d4x5t/cards/video_website?name=VWC using GIF&title=Twitter Developers&video_id=16_963269281679945728&website_url=https://developer.twitter.com"
{
"errors": [
{
"code": "MEDIA_CATEGORY_INVALID",
"message": "Media Category must be set to amplify_video while uploading video media_ids"
}
],
"request": {
"params": {}
}
}