Although I'm only on job three and have not had that much involvement with open source, I think my current employer (Attio) has one of the best codebases I've seen.

Qualitatively, I experience this in a few ways: * Codebase quality improves over time, even as codebase and team size rapidly increase * Everything is easy to find. Sub-packages are well-organised. Files are easy to search for * Scaling is now essentially solved and engineers can put 90% of their time into feature-focused work instead of load concerns

I think there are a few reasons for this:

* We have standard patterns for our common use cases * Our hiring bar is high and everyone is expected to improve code quality over time * Critical engineering decisions have been consistently well-made. For example, we are very happy to have chosen our current DB architecture, avoided GraphQL and used Rust for some performance-critical areas * A TypeScript monorepo means code quality spreads across web/mobile/backend * Doing good migrations has become a core competency. Old systems get migrated out and replaced by better, newer ones * GCP makes infra easy * All the standard best practices: code review, appropriate unit testing, feature flagging, ...

Of course, there are still some holes. We have one or two dark forest features that will eventually need refactoring/rebuilding; testing needs a little more work. But overall, I'm confident these things will get fixed and the trajectory is very good.