1) FT seemed to have changed the headline, it used to be "SoftBank’s Northstar tech unit racks up $3.7bn in losses" (refer to archive link below), which was much more specific.
The article contents are the same however - many comments below refer to $100B, however the article does not refer to Vision Fund $100B; it refers to their new "speculative trading" division, which was officially announced back in August.
2) Since this is FT, probably most people don't have access to the article due to paywall - the article itself:
3) The loss is significant, it is not 4%.
When Northstar started, Softbank announced it started with $555 million; however as of Wednesday announcement now they say Northstar manages 21B of Softbanks 43B cash pile.
3.7B quarter loss is 17.6% of 21B
4) FT has been reporting on Softbank trading for some months now - it was one of the first (or the first) to break the news about Softbank large speculative call options trades back in September (https://www.ft.com/content/75587aa6-1f1f-4e9d-b334-3ff866753...)
5) Finally, this is my personal opinion.
Softbank seemed to have built up a reputation for throwing money at companies at high valuations, with some disastrous consequences (Wework etc).
Now, it seems they are approaching trading with the same cowboy attitude; these high risk trades may work some of the time, when the market is in your favour, but when the wind changes, big losses may incur - this FT report is one indication of such losses.