The main part
As we have continued to add value to Twitch Prime, we have also re-evaluated some of the existing Twitch Prime benefits. As a result, universal ad-free viewing will no longer be part of Twitch Prime for new members, starting on September 14.
Twitch Prime members with monthly subscriptions will continue to get ad-free viewing until October 15. If you already have an annual subscription, or if you upgrade to an annual subscription before September 14, you will continue with ad-free viewing until your next renewal date.
All other Twitch Prime benefits, like monthly channel subs, monthly games and loot, and chat badges are not changing.
https://blog.twitch.tv/changes-to-twitch-prime-a986f0d8c9a9
Will have to go back to Twitch Turbo for ad free viewing once your current Prime sub ends it seems.
I live chatted Amazon this morning and got them to cancel my monthly subscription and started a full year. At least I can keep the price and no ads for another 12 months