According to Kye Gomez (@KyeGomezB), OpenMythos is an open-source, first-principles reconstruction of Claude Mythos that implements a looped transformer with Mixture-of-Experts routing to enable iterative depth via weight sharing and conditional expert activation, targeting improved efficiency and multi-step reasoning (as reported on X/Twitter). According to Kye Gomez, a community training run indicated OpenMythos achieved its best validation in 2.67× fewer steps than nanoGPT, suggesting faster convergence in early experiments (as reported on X/Twitter). According to Kye Gomez, the team is pretraining 3B and exploring 5B parameter models on the FineWeb-Edu dataset on Hugging Face, followed by GRPO and high-quality RL fine-tuning, with all artifacts to be open-sourced and training scripts available on GitHub (as reported on X/Twitter). According to Kye Gomez, this is an early-stage research effort and a theoretical hypothesis of how Claude Mythos may function, inviting community contributions to evaluate looped transformer models and MoE routing impacts on reasoning (as reported on X/Twitter).