Per their email:

An update on Prime Video

Dear Prime member,

We are writing to you today about an upcoming change to your Prime Video experience. Starting January 29, Prime Video movies and TV shows will include limited advertisements. This will allow us to continue investing in compelling content and keep increasing that investment over a long period of time. We aim to have meaningfully fewer ads than linear TV and other streaming TV providers. No action is required from you, and there is no change to the current price of your Prime membership. We will also offer a new ad-free option for an additional $2.99 per month* that you can sign up for here.

Prime is a very compelling value. Prime members enjoy a wide range of shopping, savings, and entertainment benefits, including:

More than 300 million items are available with free Prime shipping and tens of millions of the most popular items are available with free Same-Day or One-Day Delivery.
Access to exclusive and broad streaming video content (including Prime Video exclusives like The Lord of the Rings: The Rings of Power, The Boys, Tom Clancy's Jack Ryan, Citadel, The Wheel of Time, Reacher, and The Summer I Turned Pretty, as well as blockbuster movies such as Air, Creed III, Dungeons & Dragons, Candy Cane Lane with Eddie Murphy, and exclusive live sports including NFL Thursday Night Football).
Access to Prime Video Channels, which provides an unmatched selection of subscription channels like Max, Paramount+ with SHOWTIME, BET+, MGM+, ViX+, Crunchyroll, PBS KIDS, NBA League Pass, MLB.TV, and STARZ—with no extra apps to download, and no cable required. Customers only pay for the ones they want, and can cancel anytime.
The ability to use your Prime shopping benefits—like fast, free delivery, a seamless checkout experience, 24/7 live chat support, and hassle-free returns—on online stores beyond Amazon.com with Buy with Prime.
Exclusive deals and shopping events like Prime Day.
Ad-free listening of 100 million songs and millions of podcast episodes with Amazon Music.
Prescription medications as low as $1 per month and fast, free shipping from Amazon Pharmacy.
Access to unlimited eligible generic prescription medications for only $5 per month (including free shipping) with RxPass from Amazon Pharmacy.
High-quality health care from One Medical for only $9 per month (or $99 annually), with the option to add up to five additional memberships for the family for only $6 per month (or $66 annually) each.
Free two-hour Fresh grocery delivery on orders over $100 (and delivery charges between $6.95 to $9.95 for orders less than $100), and in-store savings on select groceries at Amazon Fresh and Whole Foods Market stores across the U.S.
Unlimited photo storage with Amazon Photos.
Gaming benefits with Prime Gaming.
More than 3,000 books and magazines with Prime Reading.
A free, one-year Grubhub+ membership trial valued at $120 per year, offering unlimited $0 delivery fees on orders over $12.

And, you can expect additional features and programs added in the future for our Prime members.

As mentioned above, no action is required from you. If you wish to sign up for the ad-free option, you can click here. And, as always, if you have questions about your Prime membership, you can manage your account here.

Thank you for being a valued member of Amazon Prime.

Sincerely,
The Amazon Prime team