I applied online.
Interview process can be fast moving or slow moving depending on the candidate. I was able to complete the first 3 rounds of the interview in 6 days and then the final onsite was one full day (3 hours of interviewing).
First Round: First was a recruiter call. Recruiter will talk to you to try and assess how strong of a candidate you are. Make sure you can explain the projects you worked on CLEARLY to a non-technical person. The more you can sell your project and its impact, the stronger the recruiter will rate you. After I talked to my recruiter, he said he rated me as a "Strong Candidate" and I think getting this rating early on really helped me.
Second Round: Code signal (skills assessment). I believe you can take this in Python or Javascript. I chose Python. This was a very real-world problem (build a Python class that can do certain things and create methods that fit for the prompt -> you are given unit tests as well). You do not have to get a 100% on this round to make it onto the next round. There are 3 levels and I made it to the last part of level 2 and then ran out of time. I assume STRONG senior candidates are expected to make it to level 3.
Round 3: Hiring Manager. You will talk to the person that will be your skip if you make it to this round. This round is similar to the recruiter call but you should be more technical here. Really sell yourself through the IMPACT. Recruiter told me that I got a Strong Positive signal in this round as well (this really helped me).
Round 4: Virtual onsite. There are 2 technical rounds and then the 3rd round is a conversation with the person that would be your manager. They will dig into more technical things in this round so be ready to defend your design choices.
Describe a project you recently worked on and explain it in technical depth.
The following metrics were computed from 1 interview experience for the Klaviyo Software Engineer III role.
Klaviyo's interview process for their Software Engineer III roles is incredibly easy as the vast majority of engineers get an offer after going through it.
Candidates reported having very good feelings for Klaviyo's Software Engineer III interview process.