Using google apis libraries- key required?

I'm confused about the proper use of google apis libraries. Specifically, is a key required when using Google AJAX Libraries?

This OK?:

<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js'></script>

Or is this required:

<script src="http://www.google.com/jsapi?key={myKey}"></script>
<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js'></script>

A key is not required to use the Google CDN. The first script tag above should be all you need.