SanSi: Looped Typed Decision Models for System 1.5 Thinking

Shuyu Gan, Young-Jun Lee, Dongyeop Kang · University of Minnesota · 2026
arXiv 2610.07730 Podcast

One stack, looped, read out after every loop

Drag the loop budget. The same 24 layers rerun; a typed readout gives one probability per declared option.
Loops K = 4

Compute grid: 24 layers × K loops

Schematic of work done, not measured data. Hover a cell. Same weights, repeated.Illustrative

Typed options declared by the caller

Bar heights are placeholders to show output shape: one probability per option, summing to 1.Illustrative

System 1 vs 1.5 vs 2

The Kahneman labels are the paper's framing, not evidence.

Why fixed depth hurts: liar chains (Jev API)

Reported points only: 100% at 1 step, 62.5% at 3 steps, chance from 6 steps. Dashed segments are not measured.

Lineage of looping (click a node)

Where the loss attaches

LoRA adapters on a frozen backbone

Rank 64 shared across loops, plus a small per-loop readout correction: about 60.6M shared, roughly 61M trainable.

Training recipe

Results explorer

Caveats and the RL case study

Open questions the episode raises

References

  1. SanSi — Gan, Lee, Kang, 2026
  2. Strictly Proper Scoring Rules — Gneiting, Raftery, 2007
  3. On Calibration of Modern Neural Networks — Guo et al., 2017
  4. Generative Verifiers — Zhang et al., 2024
  5. Universal Transformers — Dehghani et al., 2019
  6. Recurrent Depth / Huginn — Geiping et al., 2025
  7. Ouro: Scaling Latent Reasoning via Looped LMs — Zhu et al., 2025
  8. Adaptive Computation Time — Graves, 2016
  9. Multi-Scale Dense Networks — Huang et al., 2018
  10. PonderNet — Banino et al., 2021
  11. Shallow-Deep Networks — Kaya et al., 2019
  12. Algorithm Synthesis with Recurrent Networks — Bansal et al., 2022
  13. TTRL — Zuo et al., 2025
  14. LLM-as-a-Judge, MT-Bench — Zheng et al., 2023
  15. Language Models Don't Always Say What They Think — Turpin et al., 2023
  16. LoRA — Hu et al., 2022 (mentioned in the episode)