No, not all seasons of Vikings are currently free on Amazon Prime. However, you can watch Seasons 1-5 on Prime Video (if you have an active subscription).
To watch Season 6, you will need to buy individual episodes or the whole season on Amazon Prime Video. All 6 seasons are also available on multiple streaming services, such as Hulu and Netflix, as well as several other subscription services.
If you are looking for a more affordable way to watch Vikings, purchasing DVDs or Blu-rays of all 6 seasons is a good option. The DVDs or Blu-rays will allow you to watch all episodes of the show, as well as deleted scenes, behind the scenes featurettes, and commentaries from the cast and crew.
Also, there are many legitimate sites on the internet where you can stream or download episodes of the show for free. However, make sure to double-check the legitimacy of these sites before proceeding.
I hope this answers your question.
