What an L4 software engineer does
An L4 software engineer is given a problem rather than a task. The step up from entry level is not output but decomposition: deciding what the pieces are, in what order, and which of them is actually risky. The code is still reviewed; the plan increasingly is not.
L4 is the last level where somebody else is reliably checking the shape of your work. At L3 the task arrives specified. At L4 you are handed something the size of a feature and the breakdown is yours, which is why engineers who are fast at L3 sometimes stall here, having optimised for finishing rather than for choosing.
It is also where the foundations start to bite. Most L4 work is API design, data modelling and caching, and most L4 mistakes are a schema that was easy to write and is now expensive to change. That is not an exotic skill set. It is the ordinary one, learned properly.
The useful thing to do at this level is to close the gaps you have been routing around. If you have never sat down with how an index actually works, or what a cache does under a miss storm, that is the work.
What to actually study
Real modules from the curriculum, in the order they make sense. Every video each one points at is free.
- DeploymentThe Language of SystemsThe five behaviours every production system exhibits, stated as maths before they are stated as advice.6 lessons
- Everything DataData ModelingDesign data models that support analytics, feature engineering, training, and serving without leakage or excessive complexity.7 lessons
Common questions
- How long does it take to go from L4 to L5?
- Commonly two to four years, and unlike L3 to L4 it is not automatic. L4 is where promotion stops being a function of time and starts being a function of whether there was scope available to own. An engineer on a team with no ownable surface can do excellent work and not be promoted.
- Is L4 a junior engineer?
- No. L4 is the standard mid-level individual contributor, and at most large companies it is where the majority of engineers sit for several years. L3 is the entry band; L4 is where you are expected to work without supervision on the breakdown.
No course promotes anyone. Levels are awarded by employers against their own ladder, on evidence collected over months. What material like this can do is close a specific knowledge gap that is currently in the way.
Every level