How do I lead without authority?

The bottoms-up culture is definitely something that can take a while to get used to at Meta. My advice here is split up across 2 categories:

Get People To Like You

• This sounds obvious, but a lot of people don't realize how high the ceiling is when it comes to the skill of relationship building. More specifically, people believe that there's a limit to how quickly trust can be established and that it takes 3-6 months at least to get someone to really trust you and have your back.
• I deeply believe that if your people and communication skills are strong enough, you can get people to really like you in 3-6 days. I have met very senior engineers and managers where literally after our first 1 on 1 meeting, I thought to myself, "Wow, this person's awesome. I want to work with them as much as I can!". Here's some resources on how you can generate that effect:
  • Alex's Guide To Effective Communication - The parts about building relationships are very important.
  • [Masterclass] How To Have Impactful 1 on 1 Meetings
• As an E6, you also have a wide-range of people you could mentor: E3 to E5 is around 80% of the company. This is a bit further out (1-2 months out at least), but mentoring someone is an extremely powerful way to make a genuinely deep relationship. I gave a deep-dive about my experience with this here: [Case Study] Mentoring Junior SWEs [E3] to Senior [E5] In Just 2.5 Years At Meta
• In general, leading with kindness is very powerful. I talk about this more here: "How do you network effectively within a company?"

Back Your Case With Data

• Meta is incredibly metrics-driven; in fact, it's probably the most metrics-driven company in the world.
• Having a compelling set of data to back your project ideas and thoughts in general should be very effective in the vast majority of the company. I think WhatsApp is less data-driven alongside more 0 to 1 orgs like NPE (where they don't really have existing product data obviously).
• I recommend spending a good chunk of your data getting familiar with Meta's data tooling like Scuba, Daiquery, and Deltoid. You might want to pair program with a data scientist in your org to learn this faster.