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Core recurrence

LSTM-UT

Storing Is Not Remembering: LSTM-UT and Bounded Gated Memory for Looped Transformers

Aras Kavuncu, Muhammad Burhan Hafez

Shows on cellular-automaton tasks that keeping more history is not the same as making it usable: CoTFormer's full cache can pull corrected trajectories back toward failure. LSTM-UT adds a small, bounded, gated cell state to the shared block instead.

Inside the method

[ Shared block + gated cell state ] × N

Simplified conceptual schematic. Consult the paper for the complete architecture.

Recurrence family
Core recurrence
Depth control
Depth extrapolation far beyond training
KV / state strategy
Small bounded cell state rather than a cache of every step

Reading note

Trained to depth 12 on Rule 30, it keeps 99.7% exact-row accuracy at depth 60 where a Block Universal Transformer gets no row right, and one checkpoint stays above 99.95% at depth 1,000. On OpenWebText2 it beats BUT and roughly matches CoTFormer.

Sources checked 2026-10-28. This catalog does not imply independent reproduction.

Related works

Cite this work

@misc{lstmut2026,
  title = {Storing Is Not Remembering: LSTM-UT and Bounded Gated Memory for Looped Transformers},
  author = {Aras Kavuncu and Muhammad Burhan Hafez},
  year = {2026},
  eprint = {2609.19521},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.19521}
}

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