It seems 1 mile.
In [20]: len(api.search(geocode="-22.912214,-43.230182,1mi"))
Out[20]: 15
In [21]: len(api.search(geocode="-22.912214,-43.230182,10000km"))
Out[21]: 15
In [22]: len(api.search(geocode="-22.912214,-43.230182,1.3km"))
Out[22]: 14
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