I'm checking which tags have tag wiki excerpts in my code. It looks like /tags/{tags}/wikis is the right API since the tag info API doesn't even give a boolean for tag wiki excerpt presence.

But there's a bug where the tag wiki excerpts are not returned for the "standard meta tags": support, discussion, featured, bug. (I'm not sure if others are also affected.) These seem to be the tags with either/both of the is_required and is_moderator_only flags.

/2.1/tags/support;discussion;featured;bug/wikis?site=meta.travel

Returns:

{
  "items": [],
  "quota_remaining": 9895,
  "quota_max": 10000,
  "has_more": false
}

If it's by design that I can't retrieve the tag wiki excerpts for these then it leaves know way to distinguish between tags of this sort and tags which lack a wiki excerpt.