Occasionally I get zedtokens longer than 50 characters. It’s actually 80 characters long. What’s the max length they can get? Am I save to assume it gets never longer than 100 characters?

It depends on the datastore, and right now at least we haven't made any restrictions on possible length. Spanner and Cockroach are both basically timestamps right now, but postgres revisions return a list of in-flight txids that are used to resolve order on subsequent calls. In theory that list could be arbitrarily long. We've also talked at various points about encoding more information into a zedtoken which would also increase length

We are using Postgres. Is the recommendation then to use unlimited varchar?

ah, like for a column that would store zedtokens in an application database table?

1024

is the recommendation