At google there are SRE-SWEs and SRE-SysEng. An SRE-SWE has the same responsibilities as any SWE, but is expected to know SRE stuff. A SysEng is not expected to SWE as much, but they do both write software.

The main difference between SWE and SRE-SWE is that the latter pays better.

Thanks for explaining. Does "SRE-SWE" pay better because it's a more demanding job (pager duty to deal with network outages)?

Yeah, oncall bonus.

The message emitted as marketing to the outside world about SRE's is that they spend at least half their time writing code - improving monitoring, fault tolerance, recovery, etc. Because being called out of bed sucks.

If that's actually true is another question of course.