Currently, Portal doesn't try to deal with infinite seqs but you can deal with them in a custom submit function such as:

(require '[clojure.walk :as walk])

(defn truncate-seqs [v]
  (walk/prewalk #(if (seq? %) (take 10 %) %) v))

(add-tap (comp portal.api/submit truncate-seqs))

(tap> (range))

In very early versions of Portal, it did try to handle infinite lazy seqs, but it made the client much more complicated and I found myself not needing it very often.

@U1G869VNV Thank you!