For what it worth nearly all public models are distilled versions of bigger internal ones
I sincerely doubt the o3/2.5 pro haven't been distilled. It's unimaginable to me they're that price insensitive (or expressed inversely: were so thrifty in training that the final product can be used without optimization for the consumer usage)
the only conclusion I can come to is that they're indeed not letting you access the "root" models.
That's absolutely getting distilled down for releases.