Korean paper The Chosun Ilbo quotes an unnamed Samsung boss who claims the S4 shifted a whopping 4 million units in its first five days on sale.
Samsung reckons that by the end of this month, more than 10 million S4s will have flown off shelves.
We should note that although the unnamed Samsung boss doesn't specify, they may be talking about the number of phones sold to shops rather than the number actually taken home by customers. Still, it's a heck of a lot of phones.
The S4 is the latest in a line of best-selling S phones, following the S3, S2 and Galaxy S. Fine phones all, their quality rewarded by boffo business: between them they'd sold over 100 million last time we checked.
Even by those blockbusting standards, the S4 is selling at a mind-boggling rate. The original Galaxy S took nearly three months to hit 4m sales, the S2 took just under two months to hit that milestone, and the S3 took 21 days -- while the S4 did it in less than a week.
Samsung wants to use the good name of the Galaxy S line to sell even more phones by adding a series of spin-offs to the lineup, including the shrunken S4 Mini, camera-tastic S4 Zoom and waterproof S4 Activ (or possibly Active).
For more on the S4's illustrious lineage, hit play on our video for a trip down memory lane:
If you're thinking of splashing out on an S4, check out our guide to the best prices and deals. Does the S4 deserve to be a bestseller? Is there a better phone out there that deserves to sell well? Tell me your thoughts in the comments or on our Facebook wall.