{"slug": "can-editing-1-neuron-fix-repetition-loops-in-llms", "title": "Can Editing 1 Neuron Fix Repetition Loops in LLMs?", "summary": "Researchers found that repetition loops in Gemma 4 instruction-tuned LLMs can be fixed by editing as few as one neuron, but the fix does not resolve deeper 'doom loops' caused by missing knowledge. The study shows that while weight edits can eliminate specific generation pathologies, they cannot supply missing facts.", "body_md": "arXiv:2606.13705v1 Announce Type: new\nAbstract: Yes. Can it cure doom loops? Probably not.\nThe Gemma 4 instruction-tuned models share a reproducible failure: on long factual enumeration prompts, such as listing every episode of a TV series, the 88 IAU constellations, or the 151 original Pokemon, they collapse into repetition, either a tight verbatim loop or a list whose entries decay onto a single answer. These loops occur at rates as high as 95% and survive prompt rewording, inference-engine changes, and most sampling adjustments. In this paper we explore whether this behavior is localized enough to remove by weight edits. To localize the cause, we use per-layer ablation and per-neuron attribution, then confirm the strongest candidates with full-generation sweeps. The loops trace to a small set of MLP neurons (or, in the 26B-A4B Mixture-of-Experts model, a few routed experts) which we suppress with static weight edits. These \"surgeries\" can be as small as a single sign-inverted neuron (in the E2B model). The size of the effective edits grows with model scale, but in all cases, the loop patterns can be addressed at normal generation budgets while preserving general-purpose benchmark scores. However, the edits do not solve everything: we also study longer thinking budgets, where the two larger models most visibly enter doom looping, i.e. a non-convergent regime in which the model self-corrects in circles over a fact it cannot recall, exhausting the budget without committing to a final answer. We show this residual failure is reduced but not eliminated by the same edits, and argue it is fundamentally a knowledge-precision problem rather than a removable circuit; weight surgery can delete a loop, but it cannot supply a missing fact. Our results are both a feasibility demonstration, that is, evidence that a concrete generation pathology can be localized to a few parameters and edited out, and a delineation of where that approach stops.", "url": "https://wpnews.pro/news/can-editing-1-neuron-fix-repetition-loops-in-llms", "canonical_source": "https://arxiv.org/abs/2606.13705", "published_at": "2026-06-15 04:00:00+00:00", "updated_at": "2026-06-15 04:19:30.632583+00:00", "lang": "en", "topics": ["large-language-models", "ai-research", "ai-safety", "neural-networks"], "entities": ["Gemma 4", "arXiv", "MLP", "Mixture-of-Experts"], "alternates": {"html": "https://wpnews.pro/news/can-editing-1-neuron-fix-repetition-loops-in-llms", "markdown": "https://wpnews.pro/news/can-editing-1-neuron-fix-repetition-loops-in-llms.md", "text": "https://wpnews.pro/news/can-editing-1-neuron-fix-repetition-loops-in-llms.txt", "jsonld": "https://wpnews.pro/news/can-editing-1-neuron-fix-repetition-loops-in-llms.jsonld"}}