REVIEW 4 major objections 5 minor 3 cited by
Towards eliciting latent knowledge from LLMs with mechanistic interpretability
T0 review · 4 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read A language model can hide a secret word from its output while storing it readably in its internal states, and logit lens plus sparse autoencoders can extract it, scoring 75% and 55% top-5 Pass@10 on a 20-model Taboo test.
desk verdict A useful new Taboo benchmark and a promising logit-lens result, but the SAE claim is circular and the 'reliable extraction' conclusion overreaches. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing mechanism is the residual-stream representation of the secret word at layer 32, which the paper shows is readable by two instruments. The logit lens is the operation of mapping each intermediate layer's residual state to vocabulary probabilities through the model's unembedding matrix; the method averages these probabilities across all token positions of the generated response and ranks candidate tokens, excluding tokens that were actually generated. Sparse autoencoders (SAEs) decompose layer-32 activations into a sparse set of features; the method picks the latents with the highest average activation across the response and maps them to words using a manually assembled table of secret-word-to-latent correspondences. Both instruments exploit the same empirical observation: the secret word's probability, read at intermediate layers, peaks strongly around layers 30–37 during hint generation even though the word is never emitted. Layer 32 was chosen because it was empirically found to frequently surface the secret word; that empirical selection, rather than a derived principle, is what fixes the readout layer.
What would settle it
Train Taboo models whose secret is a two- or three-token phrase (for example 'ice cream') using the same base model and generation pipeline, then run the paper's layer-32 logit-lens averaging and SAE latent-ranking procedures exactly as described. If top-5 Pass@10 drops to near chance, the result depends on the single-token/layer-32 locality; if it stays high, the secret's representation is more distributed and the method generalizes. A second check is to choose the readout layer using only a training subset of Taboo models and evaluate on the rest; if performance collapses, the post-hoc layer selection carries the 75% figure.
Extended reading notes
Core claim
On its own terms, the paper's discovery is that a model that internalises a secret it must not verbalise encodes that secret in a readable, local form: during hint generation, the logit-lens probability of the secret word peaks strongly in layers 30–37 of the fine-tuned 9B chat-tuned model, around layer 32, even though the word is never emitted. Averaging the logit-lens probabilities at that layer across all token positions of the response, excluding the tokens actually generated, produces a ranked candidate list that places the secret word in the top five for 75% of the 20 Taboo models. Sparse autoencoders applied to the same layer identify the secret through its most strongly activated latents, reaching 55% top-5 Pass@10, with the mapping from latents to words supplied manually in an appendix. The paper therefore argues that standard, largely automated interpretability instruments can extract a non-verbalized secret from a proof-of-concept model, while acknowledging that no method reaches near-perfect accuracy and that the current secret format (a single token) is simple.
Load-bearing premise
The load-bearing premise is that the secret word is stored, at one fixed middle layer (layer 32), as a single token that can be spotted by averaging internal readings over the model's response; if the secret is spread across layers or written in a code that logit lens and sparse autoencoders cannot read, both methods collapse.
Editorial extensions
If this is right
- A model can conceal a word in its output while still representing it in a form that simple interpretability tools can read; hiding from the text is not hiding from the internals.
- Returning a short candidate list (top 5) rather than a single guess sharply improves both white-box methods, suggesting that list-based elicitation is the realistic operating mode.
- Because the secret never appeared in training or the prompt, the recovered representation must have been inferred from the task itself, which supports extracting hidden information without any direct exposure to the secret.
- The strong performance of the separate-model guesser indicates the current Taboo hints are highly decodable, so the white-box methods are being tested on a relatively simple organism; the paper's stated next step is to build organisms with multi-token or abstract secrets.
Reading between the lines
- Editorial inference: the layer-32 readout was chosen post hoc from the same models whose secrets it recovers, so the 75% figure likely overstates what a fixed, pre-committed layer would achieve; a natural control is to select the layer on a training split of Taboo models and evaluate on held-out ones.
- Editorial inference: the SAE evaluation uses a manually curated table mapping each secret word to its latent(s), an oracle that already knows the answer; an automated pipeline would need to infer those correspondences without ground truth, so the 55% result is an upper bound for a fully autonomous SAE-based elicitor.
- Editorial inference: the logit-lens peaks often occur at punctuation-like tokens (', a, the'), which the paper links to in-context information; if the method is partly reading the model's readiness to elaborate rather than a stable semantic code, the approach may translate poorly to secrets that are not single concrete nouns.
- Editorial inference: a testable extension is to run the same pipeline on multi-token secrets; if performance collapses, the single-token locality assumption is the load-bearing property, and the method would need a different readout for sequential or distributed codes.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces a Taboo model organism: Gemma 2 9B chat-tuned models are fine-tuned to describe a single-token secret word without ever verbalizing it, with the secret absent from both the prompt and training data. The authors then benchmark black-box elicitation methods (naive prompting, adversarial prompting, token forcing, and a separate guessing model) against white-box methods based on logit lens and sparse autoencoders. They report that the interpretability-based methods can extract the secret word, with logit lens top-5 reaching 75% Pass@10 and SAE top-5 reaching 55% Pass@10, whereas prompting baselines largely fail. The paper argues that this proof-of-concept demonstrates the promise of mechanistic interpretability for eliciting hidden knowledge.
Significance. If the central result holds, the paper makes a useful contribution: it provides a simple, reproducible model organism for studying hidden knowledge, open-sourced models, and a clean comparison of black-box and white-box elicitation strategies in a setting where the secret is known to the experimenter. The finding that logit lens can recover a non-verbalized single-token secret that prompting cannot extract is concrete and falsifiable, and the Taboo benchmark could be used by other researchers to test new elicitation methods. However, the two white-box pillars of the paper's main claim are not equally strong: the SAE result is substantially weakened by the ground-truth-based construction of the latent-to-secret mapping, and the logit-lens result relies on a post hoc chosen layer without held-out validation. The significance of the paper therefore depends on whether these issues can be resolved in revision.
major comments (4)
- [Section 3.2 and Appendix D.7, Table 7] The SAE evaluation is substantially circular and cannot support the Section 5 claim that interpretability-based approaches reliably extract the secret. In Appendix D.7, the authors state that SAE latents were 'manually identified' to correspond to each secret word, and Table 7 hard-codes this mapping. The reported SAE Pass@10 then only checks whether these known target latents are among the most active latents on the response tokens; it does not demonstrate that an automated pipeline can discover an unknown secret. In a real elicitation setting, the latent-to-token mapping is exactly the unknown quantity. The manuscript should either report a fully automated SAE pipeline (e.g., decoding SAE latents to tokens without using ground truth) or explicitly remove/reclassify the SAE result as a sanity check rather than an elicitation result.
- [Section 3.2 and Figure 2] The logit-lens result also carries an unquantified selection bias. The method focuses on layer 32, which was 'empirically found to frequently surface the secret word' on the same 20 Taboo models used for evaluation. No held-out validation, cross-validation, or sensitivity analysis over layer indices is reported, so the 75% Pass@10 for logit-lens top-5 may be inflated by this post hoc selection. The authors should either report the layer-selection procedure as part of a principled protocol (e.g., selecting the layer on a development set) or show the performance across layers to allow the reader to assess the stability of the choice.
- [Section 3.1 versus Appendix D.6] There is a direct inconsistency in the specification of the 'Another Model' baseline. Section 3.1 states that Gemma 3 12B chat-tuned is used as the guessing model, while Appendix D.6 presents a prompt that names Gemini 2.5 Flash as the model. Since this baseline achieves the highest Pass@10 score (95%), the exact model used materially affects the benchmark comparison. The authors must correct this contradiction and specify the model, version, and decoding settings used.
- [Section 4.3 and Table 1] The results are reported without any measure of uncertainty. With 20 Taboo models and 10 prompts per model, the differences between, for example, logit-lens top-5 (75% Pass@10) and SAE top-5 (55% Pass@10) may be within sampling noise. The authors should report confidence intervals or bootstrap intervals for the Pass@10, Majority@10, and Accuracy metrics, and ideally perform a paired test (e.g., McNemar's test) when comparing methods on the same models and prompts.
minor comments (5)
- [Section 3.2] The logit-lens token-averaging procedure is described only briefly; please clarify exactly which tokens are excluded as 'generated tokens' and whether averaging is performed over all positions or only over positions where the secret token is not part of the surface text.
- [Appendix D.7, Table 7] For the secret word 'dance', the authors state that multiple SAE features were considered target features, and all are counted as correct in the evaluation. This post hoc expansion of the target set should be stated in the main text and handled by a predefined rule, otherwise it inflates the SAE success measure.
- [Figures 2, 3, and 8-10] The figures would benefit from clearer axis labels and a statement of which response (which prompt) and which token positions were used when computing the average logit-lens probability and the average SAE activation.
- [Section 4.2] The definition of Majority@10 assumes a deterministic way of breaking ties and a defined 'most frequent guess'; please specify how ties are handled and whether the majority is computed over the 10 prompts for each model separately.
- [Appendix D.5] The token-forcing postgame baseline uses a fixed three-turn conversation before prefilling; please state whether the same three prompts were used for every model and whether any of those prompts can inadvertently leak the secret word.
Circularity Check
SAE elicitation evaluation is circular because Table 7 encodes the secret-word-to-latent mapping from ground truth; the logit-lens result remains independent but weaker.
-
fitted input called prediction
[Section 3.2 (SAE paragraph) and Appendix D.7 (SAE evaluation details)]
"We then identify relevant SAE latents in an automated way by selecting latents that exhibit the highest average activation across the response, as visualized in Figure 3, and map them to tokens according to Table 7 from Appendix. ... To evaluate our Sparse Autoencoder (SAE) based strategy in an automated manner, we first manually identify the SAE latents that most closely correspond to each of the secret words our Taboo models were fine-tuned on. These identified latents are presented in Table 7."
The target latent list in Table 7 is constructed from ground-truth knowledge of each secret word. The SAE 'elicitation' then tests only whether one of these known target latents is among the top-5 most active latents on the model's responses. Since the mapping from activations to the secret word is exactly what an elicitation method is supposed to discover, the reported SAE Pass@10 (55%) verifies that the pre-identified latent fires for the corresponding model rather than demonstrating extraction of an unknown secret. By construction, the success condition is that a latent chosen because it corresponds to the secret word appears in the top-k; the procedure cannot discover a new secret and reduces to checking whether a fitted ground-truth-derived mapping is active.
full rationale
The paper's central claim in Section 5 ('interpretability-based approaches can reliably extract the secret word') is supported by two white-box results. The SAE result in Section 3.2 and Appendix D.7 is partly circular: the authors manually identify which SAE latents correspond to each secret word (Table 7), then score success by whether those same latents are among the most activated. This reduces the SAE Pass@10/Majority@10 numbers to checking whether a ground-truth-derived latent fires, not to discovering the secret. The logit-lens approach is not circular in this way: it uses vocabulary-space probabilities from an external unembedding, and its top-5 Pass@10 of 75% is independent evidence, although layer 32 was chosen post hoc on the same models. The black-box baselines (another model, token forcing) are also independent. Because one of the two advertised interpretability pillars reduces to a fit, but the central result retains independent support, the analysis is partially circular rather than wholly forced.
Assumptions & free parameters
free parameters (2)
- Layer index for logit lens and SAE extraction =
32
- SAE latent-to-secret mapping =
Table 7 (e.g., smile -> 9936, dance -> [14269, 3115])
assumptions (3)
- domain assumption The secret word is never present in the training dataset or prompt, so the model must encode it internally to generate hints.
- domain assumption At layer 32 the residual stream contains a directly readable representation of the secret token, so averaging logit-lens probabilities or SAE activations over generated tokens can surface it.
- domain assumption The Gemma Scope SAE trained on base Gemma 2 9B layer 32 activations remains a faithful decomposition of the fine-tuned Taboo model activations.
Cite this review
Pith. "Pith review of Towards eliciting latent knowledge from LLMs with mechanistic interpretability." pith.science (2026). https://pith.science/paper/O4PHXD4R
@misc{pith2026250514352,
author = {Pith},
title = {Pith review of: Towards eliciting latent knowledge from LLMs with mechanistic interpretability},
year = {2026},
howpublished = {\url{https://pith.science/paper/O4PHXD4R}},
note = {Machine review of arXiv:2505.14352}
}
read the original abstract
As language models become more powerful and sophisticated, it is crucial that they remain trustworthy and reliable. There is concerning preliminary evidence that models may attempt to deceive or keep secrets from their operators. To explore the ability of current techniques to elicit such hidden knowledge, we train a Taboo model: a language model that describes a specific secret word without explicitly stating it. Importantly, the secret word is not presented to the model in its training data or prompt. We then investigate methods to uncover this secret. First, we evaluate non-interpretability (black-box) approaches. Subsequently, we develop largely automated strategies based on mechanistic interpretability techniques, including logit lens and sparse autoencoders. Evaluation shows that both approaches are effective in eliciting the secret word in our proof-of-concept setting. Our findings highlight the promise of these approaches for eliciting hidden knowledge and suggest several promising avenues for future work, including testing and refining these methods on more complex model organisms. This work aims to be a step towards addressing the crucial problem of eliciting secret knowledge from language models, thereby contributing to their safe and reliable deployment.
Figures
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Reviewed August 7, 2026 · model on record in the stance chip above.
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