Keep in mind that it's not 900 engineers. At the time Instagram was bought by Facebook, (and still I think) they didn't have any kind of ads and thus no need f

Keep in mind that it's not 900 engineers. At the time Instagram was bought by Facebook, (and still I think) they didn't have any kind of ads and thus no need for sales people and a reduced need for engineering, product management, biz dev, etc. as well. Media outlets hadn't really picked up on Instagram yet (at least, not as a tool to use themselves), so no need for media relations people. They didn't really need biz dev people yet like Twitter certainly does. (e.g. you need people to make the integration of Twitter in other platforms like iOS and OS X happen) Also, Twitter is older than Instagram. Over time, if success is still going, it's somewhat normal to increase your staff just because there are things you can improve all over the place (product-wise as well as company-wise). And now that Instagram is part of another company, it's hard to compare the numbers since they might take advantage of Facebook resources here and there which are hard to account for.