Jameson Lopp's own site lists his role as "Co-founder & Chief Security Officer" at Casa. Casa's blog says the same and adds a date to the work: "he has been building bitcoin wallets since 2015."
The public output is mostly writing and tooling rather than product announcements. He maintains long-running reference material on self-custody, key management and node operation, and publishes analyses of how wallets fail in practice, which is a rarer genre than how they are supposed to work.
At Casa the security brief covers the part of self-custody most people get wrong: not the signing, which hardware handles, but recovery. A multi-key setup is only useful if losing one key is survivable and losing the holder is survivable too, and both are procedures rather than features.
This entry covers his public professional capacity only.