How do I become a senior engineer if my company doesn't formally have titles?

Two questions to ask if you are senior:

1. Who do people turn to get unblocked on your team?
2. How far in advance do you know what you’ll work on? Senior engineers should forecast out further.

Once you have calibrated the above with people around you, then talk to your manager about the expectations and define what it means to meet or exceed expectations. At a startup, there’s more burden on you to define “success”.

For context, a senior engineer at a Big Tech company is often referred to as an "L5", which stems from the somewhat standardized Google-leveling system.

These are the core attributes of a solid L5 engineer from my experience:

• Ability to lead a team of 5-10 people
• Can be given entire, often ambiguous projects spanning 3-6 months and executes on them with near 0 hand-holding
• Strong mentor for a couple mid-level (L4) and entry-level (L3) engineers, moving them faster than average along the promotion path than SWEs without a mentor
• Strong XFN communication skills, especially if working on the product side. Will get glowing feedback from PMs, designers, data scientists, etc in performance review
• Very, very strong technical proficiency. Writes extremely high-quality diffs and leaves very insightful feedback in code review, catching issues L4s and L3s can't