50–60% are Google Software Engineers, or more precisely, people who have been hired via the standard procedure for Google Software Engineers. The other 40–50% are candidates who were very close to the Google Software Engineering qualifications (i.e., 85–99% of the skill set required), and who in addition had a set of technical skills that is useful to SRE but is rare for most software engineers. By far, UNIX system internals and networking (Layer 1 to Layer 3) expertise are the two most common types of alternate technical skills we seek.
