From skimming the linked PR it looks like it's all been open source, but has been tightly coupled to their deployed instance. The PR appears to be decoupling things completely by making all hard coded values configurable.

Always been able to host it! We’ve had docker compose instructions since open sourcing.

Instant has evolved quite a bit in the last 18 months. With all the new functionality self-hosting has become a bit more fiddly.

This PR is aimed at making the process for self-hosting even easier.