Amazon doesn't publicly disclose how many Amazon Prime members it is the U.S., or globally for that matter. But late last year, research company Parks Associates published data suggesting that Prime Video has surpassed Netflix in U.S. subscriber count.

From the article, "Amazon Touts JustWatch Report Saying It Beat Netflix in Q2 Engagement ... 'Take Our Market Share Data With a Grain of Salt,' Responds JustWatch's Founder" by Daniel Frankel.
Data is really the new area of competition. If the pay-TV providers are looking at competition long-term in the future, that's the main concern. - BRETT SAPPINGTON, DIRECTOR OF RESEARCH AT PARKS ASSOC...
Roku faces myriad competitors, but it still dominated the U.S. streaming device market with a 37% share as of early 2018, according to Parks Associates. Amazon ranked second with a 28% share, and Appl...
The Roku Channel is also turning heads. The company's ad-supported channel was named one of the three best ad-based over-the-top services among U.S. broadband households according to Parks Associates,...
Pay-TV operators are seeing a "slow erosion of the core business," analyst Brett Sappington at Parks Associates said. "After years of attempts to be more than just a 'dumb pipe,' pay-TV operators h...