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I was surprised that I couldn't find any uploads of this.
This is "portal2_reconstructing_science.wav" from the Console versions of Portal 2. It was uncovered by @ToothpasteVixen, who was also the person who sent it to me.
This version of the song is referenced in "scripts/game_sounds_music_a4.txt," where the script would have originally played it immediately after Want You Gone finished (I think, sound operators aren't very well documented on the Valve Developer Wiki.)
This version is slightly different to the Russian OST's "Nano Mix" (   • Portal 2 soundtrack - Reconstructing ...  ) and you can hear the difference the most at around 0:05.
This song belongs exclusively to Valve Software. Any attempts by anyone to reupload the music and claim it as their own to make ad revenue should be reported to Valve directly through their contact form. I claim no ownership over this song.