Currently it seems the only episode up is Night of the Sentinels Part One, but according to the official Marvel Twitter HERE: "...You can also watch the '90s X-Men animated series for free on Marvel.com..."
Hopefully this will mean the full length complete series for those of us that aren't able to get our hands on the DVDs yet. And for a price we can all agree on... Free!
You can also check out more of your favorite Marvel based TV Shows on Marvel.com, such as X-men: Evolution, and the new Wolverine and the X-men.
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Your friendly neighborhood Falcon,
FalconX2
[John A.]