Scaling, reliability, support, dialects and localisation, accessibility, edge cases, device support, security, moderation (not just moderators but moderation tools) infrastructure, research and exploration, monetization, commercialization. Basically everything no one in a startup thinks about for years if not more. And to that add the simple fact that as the team grows the per engineer productivity just has to drop due to communication overhead among other things.

> device support

For the record I think the device support used to be better before when they supported pre-android Nokias as well.

Yes, in the early days it ran on 6-7 different platforms. Back then it was about 1-3 developers per platform, however. Small focused teams like that can have significantly higher per-developer productivity, but are far more limited in the breath and nuance of what they can work on.

As a project grows in scale, there are a lot of development tasks that take a significant amount of time and effort for relatively little user-visible impact. However, in aggregate, there is a benefit to investing in those sorts of things.

For me WhatsApp has gone from my favorite app to something I won't touch except almost as last resort.

I had no issues with old WhatsApp whatsoever and I'm not aware of anyone else having any either and I'm part of multiple groups that used to use it extensively.

The only thing that has improved meaningfully since then is end-to-end encryption, but as much as I love that it is only nice-to-have for me and I would feel a lot safer with just ordinary encryption as long as Facebook wasn't snooping in my contacts and metadata.

I understand that the 1K+ engineer number comes from Facebook as a whole, when mentioning the use of Hack as a typed PHP.

More like to give a perspective on the transition on how to come from a small company into a huge one.

WhatApps got audio and video calls after the Facebook acquisition.

Usage increased by a few orders of magnitude too.

Yeah I think people get usage confused with number of users.

That explains it. I haven’t used WhatsApp until few months ago

No global service can run with 10 people. Just to have a good coverage 24/7 you're looking at a 50 people company.

Yeah, just ops would be 3 timezones x 8 hours x 2 (ideally 3) people per timezone. So that's 6-9 people just for a barebones ops team.

Do you know of any company that runs a product with this many users globally on 100 people let alone 10?

Old WhatsApp?