
“Looping a transformer increases no-CoT capabilities more than general capabilities” by Alek Westover, Nick Kuhn
Some researchers worry that looping (as in looped transformers) is a particularly scary way to make AI models more capable, because looped models will be harder to monitor than standard transformers of similar capability. We test this worry on NVIDIA's Dory 4B, a publicly available looped transformer, and find evidence that it is justified.
Result 1. Looping boosts no-CoT reasoning much more than it boosts general capabilities.
Dory can run with a configurable number of loops. It was trained to use up to 4 loops, and adding loops up to 8 at inference time still improves performance. Without looping, Dory's no-CoT capabilities (measured by NCRI, the No-CoT Reasoning Index) match what a trend fitted to open-source models predicts from how well it predicts text (measured in bits-per-byte). Its general with-CoT reasoning capability (measured by “mini-ECI”, a custom, smaller version of Epoch's Capabilities Index) is high relative to its NCRI, so Dory sits below the NCRI-vs-mini-ECI trend, but it is similar to the best models of its size. Adding loops improves mini-ECI and bits per byte only slightly but increases NCRI substantially. In fact, if we plot NCRI against total parameters, counting looped parameters once per loop, NCRI rises faster [...]
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Outline:
(05:39) Result 1: Looping boosts no-CoT reasoning much more than general capabilities
(12:09) Result 2. Dory has no CoT controllability
(13:31) Result 3. Recurrent-Dory can evade monitors
(21:13) There are two images here. First: en-US-AvaMultilingualNeural__ Four line graphs titled "Cfgpatch (chain length 4-8): GRPO against a CoT monitor," comparing normal-Dory and recurrent-Dory. Second: en-US-AvaMultilingualNeural__ Four-panel line graph: "Arithmetic (6-12 operations): GRPO against a CoT monitor" comparing normal-Dory and recurrent-Dory.
(21:42) Result 4. Capabilities uplift under recurrent KV sharing
(23:58) Limitations and Future Work
(24:24) Conclusion
(24:50) Further experiments on a larger looped model
(28:09) Appendix
(28:12) A. Repeating the question boosts NCRI (only) when Dory is looped
(28:31) A.1 Filler token uplift
(29:50) B. More about CoT controllability
(30:25) B.1 CoT + output length
(31:13) C. Additional figures
(31:17) C.1 Output controllability by rule
(31:32) C.2 Thinking-on Reasoning index (NCRI, but with CoT) vs mini-ECI: Astra/6.1 Sol are still better.
(31:55) C.3 NCRI with thinking on vs bpb
(32:14) C.4 Capability metrics vs. pretrain compute and tokens
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First published:
November 12th, 2026
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Narrated by TYPE III AUDIO.
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