SG&A, which includes sales & marketing, grew 3.06x since 2019 -- so linearly with revenue growth, as is typical for enterprise B2B.
And on the engineering front: If they're not investing substantially in R&D, then they're likely going to flame out in the coming decade. R&D expense grew 2.62x in the same timeframe.
How much of their revenue came in because of acquisitions like Segment?
That said, sustainable growth is ok, Twilio's head count growth was "wild" to put it mild.