1462
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.
Keep in mind that the game has been in Early Access for almost three years. Anybody who played the game in that span but hasn't launched it since yesterday is going to push that percentage down.