They're saying they expect to generate $100M revenue this year. I think that places them a bit further off the $1B _exit_ than 8x, although if they raised further funding potentially that could be done at an amount that suggests a $1B value.

I wouldn't want to be competing against AWS Pinpoint, and the problems Twilio have suggests this is a technically difficult space. Seems like quite a big bet from the VCs involved.