Trinity-Large-Thinking vs OpenMythos

Trinity-Large-Thinking is a 399-billion-parameter open mixture-of-experts (MoE) reasoning model from Arcee AI, released under Apache 2.0. It's designed specifically for long-horizon multi-turn tool use and autonomous agentic tasks — thinking before responding with an explicit reasoning chain. The model ranked #2 on PinchBench (behind only Claude Opus 4.6) while costing $0.90/M output tokens via the Arcee API — roughly 96% cheaper than Opus. The full weights are freely downloadable from Hugging Face, making it one of the most capable openly-downloadable models available anywhere. Architecturally it draws on MoE efficiency to activate only a fraction of parameters per forward pass, enabling the massive 399B count without proportional compute cost. For teams building production agents that need serious reasoning but can't afford closed-model pricing at scale, Trinity-Large-Thinking is the most compelling open alternative that's appeared in a long time.

OpenMythos is a community-driven theoretical reconstruction of Claude Mythos's suspected architecture, implementing a Recurrent-Depth Transformer (RDT) — a looped transformer that recycles layers multiple times per forward pass for deeper reasoning without massive parameter growth. The project drew 10,100 GitHub stars in its first week, reflecting intense developer curiosity about what's powering Anthropic's latest generation models. The architecture has three stages: a Prelude (initial layers), a Recurrent Block (looped up to 32 times with shared weights), and a Coda (final layers). Rather than stacking hundreds of unique layers, the recurrent block runs the same weights multiple times with learned injection parameters updating hidden states between loops — enabling implicit chain-of-thought reasoning in continuous latent space without generating intermediate tokens. The project supports Grouped Query Attention (GQA) with optional Flash Attention 2, Multi-Latent Attention (MLA), and sparse MoE with routed and shared experts. Model scales range from 1B to 1T parameters. The key claim is that RDT achieves reasoning depth comparable to fixed-depth models with far more parameters, since computational complexity scales with loop iterations rather than layer count. This would explain how Claude Mythos achieves strong reasoning performance without the extreme parameter counts of brute-force scaling — though Anthropic has neither confirmed nor denied the architecture.