The City Tax is CHF 3.50 per guest per overnight stay. The rate was increased from CHF 2.50 to CHF 3.50 in May 2023. The source does not state any adult/child tiers or other rate levels.
No exemptions or reduced rates are specified in the official sources consulted. The official municipal report says the City Tax concerns Zürich Tourism members (typically hotels), while the current city information also refers to Airbnb hosts.
The source says that the City Tax is collected per overnight stay from hotels and Airbnb hosts/landlords. It does not provide further short-term-rental rules, exemptions, collection procedures, or a separate Airbnb rate.