Flag fields were removed from JSON output and optional fields will now get nulls instead of zero values. For example, "FromID":0 -> "FromID":null, "URL":"" -> "URL":null, etc.
More details here https://github.com/3bl3gamer/tgclient/releases/tag/v0.166.2

Fixed casing for some fields. For example, Dc -> DC, Ids -> IDs, Ipv4 -> IPv4, savedGifs -> savedGIFs, etc.
More info here https://github.com/3bl3gamer/tgclient/blob/b35be886dd3595eb9dc54528c855316ebca0d1f9/mtproto/scheme/generate_tl_schema.go#L95

Some blank history/users and history/chats fields will now be saved as nulls instead of empty strings (Username, FirstName, LastName, PhoneNumber).

history/users now have IsDeleted boolean field.