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When Baldur's Gate 3 came out, Steam's overall bandwidth consumption went from around 18 Tbps to 146 Tbps
(reddthat.com)
From Steam's self-published stats.
Baldur's Gate 3 could not be preloaded and weighed in at 125 gigabytes on disk, so when the game left Early Access at 11am US Eastern yesterday, Steam's bandwidth utilization shot up 8x over a span of 30 minutes. I know personally, I saw my download hit over 600 Mbps across a 1 Gbps fiber connection.
Kudos to the system engineers at Valve. It is mind-boggling that they have built infrastructure that robust.
Microsoft's implementation of the feature is called Windows Update Delivery Optimization.
https://support.microsoft.com/en-us/windows/windows-update-delivery-optimization-and-privacy-bf86a244-8f26-a3c7-a137-a43bfbe688e8
Here's a short optimisation guide: https://www.ctrl.blog/entry/windows-delivery-optimization.html
Fundamentally it's not like the Bittorrent protocol, even though there are similar behaviours and the result is the same. Microsoft retains the ability to stop the network from seeding updates and has ways of only targeting specific supported configurations to receive new updates.