https://en.wikipedia.org/wiki/List_of_the_most_distant_astronomical_objects

Only objects count, and only those that can unambiguously be said to have been observed. If there's ambiguity over whether something should count, I'll go by the Wikipedia page's judgement after it looks like any active debate about it has died down.

The current highest as of market creation is z=14.32. For comparison, the CMBR has z=1089, which is the upper limit on how old an observable object can be.