2025 Access fee info from "Travel Updates and Insights" Blogs:
https://blog.ricksteves.com/insights/venice-access-fee/
That 2025 period has ended, and it remains to be seen if governing bodies of the Municipality of Venice will reinstate the fee or required registration for 2026 and for which specific dates. It only applied to certain dates in April, May, June and July this year (https://cda.veneziaunica.it/en/access-fee.)
Note that the blog piece linked states that, "If you’re on a Rick Steves tour that goes to Venice, we’ll soon be providing details on exactly how to claim your exemption. In a nutshell: If your visit to Venice occurs in the middle of the tour itinerary, we’ll take care registering on your behalf; but if your tour begins in Venice, that means you’ll be arriving on your own…and will need to register yourself." I would assume that info still holds if the Access Contribution applies next year.
Past forum threads on the subject:
https://search.ricksteves.com/?button=&date_range=2y&filter=Travel+Forum&query=Venice+Access+fee&utf8=✓