I'm looking to level up and am currently designated as an SWE-2, where I take end-to-end responsibility for an Android app. I have a couple of juniors who report to me. I also took responsibility for writing backend APIs.
I even led a feature using guidelines of system design playlist and made a brag journal for promotions.
What are the exact behaviors to become one level up as SWE-3 (Mid-level)?
Depending on the company, it sounds like your scope is more than enough for a senior engineer. For context, at a company like Pinterest or Meta, a mid-level engineer would be responsible for a single feature on one platform. You've gone far beyond that, owning the entire Android app and also dipped into the backend/API layer. So scope is certainly not the problem.
The other ingredient for a senior-level promotion is that you have gained the trust of the people around you (both the people you're mentoring and the leadership team). What has been the reception of the system design you presented, and the features you deliver on the Android app? Do people assume you will deliver the feature on time with high quality, or do they request detailed updates and code review?
Finally, the last part is the business need for promotion. Unfortunately, this is out of your control. The business must have the budget and requirement for someone to step into a senior position. This is usually not a problem at a growing startup, nor is it common for a senior engineer. It's more common at leadership levels, e.g. do we need another Director in the company? This is probably not impacting you, but I'd have that conversation with your manager.
Rahul, can you link some lessons to help me align and solidify my behaviors?
There are 2 live events that I thought covered the behavior differences at more senior levels:
In addition, I'd encourage you to filter Taro questions by senior engineers, and explore all the content related to senior engineer here: https://www.jointaro.com/topic/senior-engineer/