Right now that is not possible out of the box because the URL path is hard-coded to accommodate potential future future versioning.
The issue with running it at the root domain level is that cAPI loads the Joomla application *through* the Slim application and the routing is completely independent of the Joomla router.
There is another option though. I think you could use a CNAME to mask
as api.mydomain.tld at the DNS zone level. I have not tried this yet but it should work (as long as I haven't hard-coded /api/v1 paths!).
We can follow-up in the support area if you need further assistance with such a solution.