My bar for a senior engineer is someone who can independently drive a large (1 quarter-ish) project to completion with high quality, acting primarily as an IC.

My bar for a senior engineer is someone who can independently drive a large (1 quarter-ish) project to completion with high quality, acting primarily as an IC. They're someone I can throw at a problem and get it solved. They'll by and large get themselves unblocked when stuck - asking questions, talking to stakeholders, etc. They can decompose problems so that other less senior engineers on the team can execute on different parts of them efficiently.