That was the first public release. There used to be a History.md file in the repo with the January date. There was a lot of experimentation even before that - browsers started adding experimental WS support on the second half of 2009, right as node was gearing up. Some artifacts from that era:
Another thing to keep in mind is that the precursor SSJS environments like Jack/Narwhal, Helma etc probably added it even earlier. Hard to tell since GitHub itself was new and many of these sources are hard to find today.