I don't think the generators themselves were open-sourced (only the generated SDKs were already open-source). That leaves three main (recommended) options:

* Manual Maintenance: Returning to the pre-Stainless era.

* Agentic Coding: Works to an extent, but you lose the deterministic, review-free output required to keep an SDK perfectly structured and coherent.

* Open-source Generators: Helpful for basic use cases, but they lack Stainless's full-stack features like multi-language generation and publishing, MCPs, and documentation.