OpenMythos

The Panel's Take

OpenMythos is a PyTorch reconstruction of the suspected architecture underlying Anthropic's Claude Mythos model, built entirely from published research. Creator Kye Gomez hypothesizes that Mythos uses a Recurrent-Depth Transformer (RDT) — where a subset of transformer layers loops multiple times per forward pass with shared weights rather than stacking unique layers. This allows the model to simulate "thinking" by iterating over the same compute graph, giving it emergent chain-of-thought behavior without explicit CoT prompting. At 770M parameters, the OpenMythos implementation reportedly matches the downstream quality of a 1.3B standard transformer on benchmarks. The architecture combines Multi-Latent Attention for memory compression, LTI (Linear Time-Invariant) stability constraints to prevent training instability during recurrence, Mixture of Experts routing for specialization, and Adaptive Computation Time (ACT) halting to decide when to stop looping per token. The project exploded on GitHub within days — 6.2k stars, 1.2k forks — and Kye's X announcement drove massive engagement (4.1k likes, 4.5k reposts). Community reaction is genuinely divided: AI researchers calling it "the most sophisticated reverse-engineering of an LLM architecture I've seen" while Anthropic has not confirmed or denied any of the architectural claims. This is an educated speculation backed by real engineering, not a marketing exercise.

OpenMythos verdict: SHIP 🚀

3 ships · 1 skip from the expert panel

Full review: shiporskip.io/tool/openmythos-claude-mythos-recurrent-depth-transformer-pytorch-reconstruction-2026

Builder

Ship

“Whether or not Anthropic actually uses this architecture, the RDT implementation itself is genuinely impressive engineering. The ACT halting mechanism and LTI stability constraints are clever solutions to problems anyone trying to build reasoning models will face. Fork-worthy regardless of the Mythos speculation.”

Skeptic

Skip

“This is reverse engineering based on vibes and published papers, not leaked weights or verified architecture docs. Anthropic hasn't confirmed a thing. The 770M benchmark comparisons are cherrypicked and the '1.3B equivalent quality' claim needs independent reproduction. Intellectually interesting, empirically unverified.”

Futurist

Ship

“Regardless of whether Mythos actually is an RDT, this project demonstrates that open-source researchers can meaningfully reconstruct competitive reasoning architectures from scratch. That capability gap between frontier labs and open-source is closing faster than most realize.”

Creator

Ship

“A 6.2k star project in two days means something hit a nerve. The documentation is excellent — clear architecture diagrams, detailed training notes, working code. Even if the Mythos speculation is wrong, this is a model for how to share research engineering properly.”