XF 2.2 Are "similar threads" a built-in feature, or an addon?


I was googling how to enable "similar threads" in Xenforo, just like this forum has enabled. And found a paid 3rd-party addon for it. But I was thinking that if it's a part of the official support forum then surely it must be a built-in feature.
Can someone clear up this confusion please?

Edit: With further googling it seems it's available as part of the enhanced search addon.
If this is the case then I'm very dissapointed. I will never pay extra for features which should be standard by default.
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