Price discrimination for services is mostly legal
Look at the wedding industry. Get a bunch of quotes on floral work. Then get a bunch of quotes for the same work, but tell them the event is a wedding. Oh, hey, look, you're getting charged 30% or beyond extra.
(I am not a full-time wedding photographer, but have shot maybe 20 weddings, and heard of this multiple times.)
Imagine if it were Comcast instead of Claude. Comcast gives you 750GB of data a month. Now they decide that visiting HN 'counts' as 750GB and either shut you off or bill you extra. Is that price discrimination or changing the terms after the fact?