Is build 10581 released?

Nope it hasn't been released yet. The video posted on YouTube could be an internal build running on the 635.
 
581 has been released this morning for phone.
576 is < supposed > to be released this afternoon for desktops / tablets but so far 2:30 pm almost ... no 576.
 
Since you're talking about "Insider App", I'm assuming you are talking about the Mobile version. Yes, 10581 is available for W10 Mobile, and 10576 is available for PC.

Note that it became available about 2-1/2 hours after the opening post of this topic.

You don't have to ask in the forums whether a build has been released. Just check the windowscentral.com, and there will be an article posted once a release hits. Always. PC Build, Mobile Build, they keep them all covered and tell you what you need to know. If there is no article, then either a build hasn't been released, or it's only been released for less than 5 minutes, because they are pretty fast about getting the article up for us to see.
 

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