SCIT: Testing Causal Cache Carriers in Latent Chain-of-Thought Models

YI Ding, Lijun Huang, Menglin Yang


Abstract
Latent chain-of-thought models move intermediate reasoning into continuous states, obscuring which internal object causally carries a computation. We introduce SCIT, the Suffix Cache Interchange Test, which patches exact source–recipient counterfactuals and crosses cache-segment sufficiency with K/V splits, hidden-state and semantic-source controls, decoded validation, and matched corruption. In GPT-2 arithmetic, counterfactual transfer concentrates in value-cache suffix trajectories rather than hidden states, keys, answer slots, or single-token triggers. Full sufficiency-and-necessity closure holds only for the main CODI-GPT2 checkpoint; the Sim-CoT-style reproduction supports sufficiency and decoded transfer but not necessity. Across broader competent cells, arithmetic-like GPT-2/1B tasks retain latent-tail value/KV transfer, whereas 8B and repaired non-arithmetic tasks shift to prompt-prefix or full-cache K/V; ungated cells receive no call. SCIT thus provides a cache-level diagnostic, a checkpoint-specific arithmetic mechanism, and a competence-gated carrier map—not a universal latent-tail claim. Code: https://github.com/YIDING4869/scit-emnlp-2026
Anthology ID:
2026.findings-emnlp.846
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
17905–17946
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.846/
DOI:
Bibkey:
Cite (ACL):
YI Ding, Lijun Huang, and Menglin Yang. 2026. SCIT: Testing Causal Cache Carriers in Latent Chain-of-Thought Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 17905–17946, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
SCIT: Testing Causal Cache Carriers in Latent Chain-of-Thought Models (Ding et al., Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.846.pdf