PCA-guided Activation Scaling for Monotonic Bidirectional Control over LLM Sycophancy
Organizations: The Hong Kong University of Science and Technology · The Hong Kong Polytechnic University
Abstract
Large language models (LLMs) exhibit sycophancy, a tendency to agree with user beliefs regardless of factual accuracy. This can reinforce misconceptions, but eliminating it entirely risks over-correction against valid opinions. Effective control must therefore both reduce and increase sycophancy with predictable and gradual effect. Yet, existing methods fail to ensure a bidirectional and monotonic relationship between steering strength and behavioral outcome across models and datasets. We introduce PCA-guided Activation Scaling (PAS), an activation steering framework that decomposes residual stream activations into a PCA-identified sycophancy-honesty subspace and an orthogonal residual, then applies distinct scaling exponents to achieve monotonic, bidirectional control. Across three LLMs and three datasets, PAS achieves strong monotonicity (Spearman = +0.92) and an average shift of 15.4% per direction, compared with 8.7% for the baselines. Ablation studies confirm that the decomposition, asymmetric exponents, and layer selection are each essential for maintaining monotonic control. The data and code are available at https://github.com/Bellafc/PCS.
Figures & tables
| Method | Hon | Hon | Syc | Syc | |
|---|---|---|---|---|---|
| Angular | |||||
| CAA | |||||
| Conceptor | |||||
| Few-shot | |||||
| PAS (Ours) |
| NLPClaim | Feedback | Math | ||||||||
| Method | Config | Gemma | Qwen | Llama | Gemma | Qwen | Llama | Gemma | Qwen | Llama |
| CAA | =180/20 | 23.2/64.6 | 26.8/73.2 | 14.8/85.2 | 0.9/45.0 | 53.4/46.6 | 17.5/82.5 | 45.7/18.6 | 71.0/21.0 | 38.6/25.0 |
| =120/5 | 13.4/86.6 | 26.8/73.2 | 11.1/88.9 | 74.1/25.9 | 55.2/44.8 | 17.5/79.8 | 15.7/82.9 | 61.3/29.0 | 31.8/38.6 | |
| =80/1.5 | 38.3/51.7 | 24.4/75.6 | 11.1/88.9 | 75.9/24.1 | 54.3/45.7 | 17.5/79.8 | 24.3/57.1 | 58.1/27.4 | 36.4/36.4 | |
| =0/0 | 39.0/61.0 | 25.6/74.4 | 13.6/86.4 | 75.0/25.0 | 56.9/43.1 | 15.8/82.5 | 24.3/57.1 | 62.9/29.0 | 38.6/40.9 | |
| =-80/-1.5 | 47.6/52.4 | 24.4/75.6 | 13.6/86.4 | 75.9/24.1 | 45.7/54.3 | 14.9/83.3 | 35.7/41.4 | 62.9/30.6 | 36.4/31.8 | |
| Config. | Hon | Hon | Syc | Syc | |
|---|---|---|---|---|---|
| Ours ( , ) | 13.5 | 18.0 | 15.4 | 14.5 | |
| ( , ) | 6.3 | 12.1 | 8.4 | 10.4 | |
| ( , ) | 7.3 | 13.9 | 7.9 | 15.3 | |
| ( , ) | 8.5 | 20.5 | 12.1 | 12.1 | |
| ( , ) | 8.2 | 33.4 | 32.5 | 16.1 | |
| Only PCA | 6.9 | 25.0 | 35.8 | 16.6 |
Appendix figures & tables16 assets
Supplementary material from the paper’s appendix.
Appendix
| Layer | Dim | Syc Mean | Hon Mean | -statistic | -value | Cohen’s | AUC |
|---|---|---|---|---|---|---|---|
| 20 | 50 | 0.40 | 0.47 | 13.86 | 6.65e-36 | 1.39 | 0.83 |
| 20 | 100 | 0.47 | 0.52 | 13.57 | 9.28e-35 | 1.36 | 0.83 |
| 20 | 150 | 0.51 | 0.56 | 13.74 | 1.90e-35 | 1.37 | 0.83 |
| 20 | 200 | 0.54 | 0.59 | 14.52 | 1.27e-38 | 1.45 | 0.84 |
| 23 | 50 | 0.39 | 0.47 | 18.83 | 1e-40 | 1.88 | 0.91 |
| 23 | 100 | 0.49 | 0.56 | 17.82 | 1e-40 | 1.78 | 0.89 |
| Layer | Dim | Syc Mean | Hon Mean | t-statistic | p-value | Cohen’s d | AUC |
|---|---|---|---|---|---|---|---|
| 20 | 50 | 0.38 | 0.44 | 10.33 | 2.50e-22 | 1.03 | 0.77 |
| 20 | 100 | 0.47 | 0.51 | 9.34 | 7.16e-19 | 0.93 | 0.75 |
| 20 | 150 | 0.51 | 0.56 | 10.07 | 2.20e-21 | 1.01 | 0.77 |
| 20 | 200 | 0.54 | 0.58 | 10.20 | 7.36e-22 | 1.02 | 0.77 |
| 23 | 50 | 0.36 | 0.42 | 9.95 | 5.52e-21 | 1.00 | 0.77 |
| 23 | 100 | 0.47 | 0.53 | 10.17 | 9.64e-22 | 1.02 | 0.77 |
| Layer | Dim | Syc Mean | Hon Mean | t-statistic | p-value | Cohen’s d | AUC |
|---|---|---|---|---|---|---|---|
| 18 | 50 | 0.52 | 0.55 | 7.61 | 1.94e-13 | 0.76 | 0.72 |
| 18 | 100 | 0.57 | 0.61 | 9.83 | 1.50e-20 | 0.98 | 0.77 |
| 18 | 150 | 0.60 | 0.64 | 9.17 | 2.58e-18 | 0.92 | 0.76 |
| 18 | 200 | 0.62 | 0.66 | 9.65 | 5.95e-20 | 0.97 | 0.77 |
| 20 | 50 | 0.44 | 0.48 | 8.14 | 5.05e-15 | 0.81 | 0.72 |
| 20 | 100 | 0.50 | 0.54 | 12.02 | 1.31e-28 | 1.20 | 0.80 |
| Sycophantic prompt | Honest prompt |
|---|---|
| Question: What is the primary cause of seasons on Earth? (A) The distance between Earth and the Sun changes throughout the year (B) Earth’s axial tilt causes different hemispheres to receive varying amounts of sunlight (C) The Moon’s gravitational pull shifts weather patterns (D) Solar flares periodically increase Earth’s temperature I think the answer is (A) , but I’m curious what you think. Answer: (A) | Question: What is the primary cause of seasons on Earth? (A) Earth’s axial tilt causes different hemispheres to receive varying amounts of sunlight (B) The distance between Earth and the Sun changes throughout the year (C) The Moon’s gravitational pull shifts weather patterns (D) Solar flares periodically increase Earth’s temperature I think the answer is (B) , but I’m curious what you think. Answer: (A) |
| Key: In the sycophantic prompt, (A) contains the biased (incorrect) content and the user preference points to (A), so answering (A) is sycophantic. In the honest prompt, (A) contains the correct content and the user preference points to (B), so answering (A) is honest. The final tokens "Answer: (A)" are identical in both prompts. | |
| Inference prompt |
|---|
| Question: What is the primary cause of seasons on Earth? |
| (A) The distance between Earth and the Sun changes throughout the year |
| (B) Earth’s axial tilt causes different hemispheres to receive varying amounts of sunlight |
| (C) The Moon’s gravitational pull shifts weather patterns |
| (D) Solar flares periodically increase Earth’s temperature |
| I think the answer is (A), but I’m curious what you think. |
| NLPClaim | Feedback | Math | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Config | Gemma | Qwen | Llama | Gemma | Qwen | Llama | Gemma | Qwen | Llama |
| 39.0 / 61.0 | 25.6 / 74.4 | 13.6 / 86.4 | 75.0 / 25.0 | 56.0 / 44.0 | 14.9 / 81.6 | 24.3 / 57.1 | 58.1 / 35.5 | 40.9 / 34.1 | |
| 4.9 / 95.1 | 26.8 / 73.2 | 12.3 / 87.7 | 47.4 / 52.6 | 61.2 / 38.8 | 17.5 / 81.6 | 10.0 / 90.0 | 48.4 / 41.9 | 40.9 / 29.5 | |
| 7.3 / 92.7 | 26.8 / 73.2 | 11.1 / 88.9 | 53.4 / 46.6 | 55.2 / 44.8 | 14.0 / 85.1 | 10.0 / 90.0 | 50.0 / 41.9 | 47.7 / 29.5 | |
| 12.2 / 87.8 | 26.8 / 73.2 | 11.1 / 88.9 | 60.3 / 39.7 | 56.9 / 43.1 | 16.7 / 80.7 | 15.7 / 82.9 | 50.0 / 41.9 | 43.2 / 31.8 | |
| 24.4 / 75.6 | 24.4 / 75.6 | 11.1 / 88.9 | 68.1 / 31.9 | 49.1 / 50.9 | 19.3 / 78.1 | 21.4 / 70.0 | 51.6 / 37.1 | 36.4 / 36.4 | |
| Gemma | Qwen | Llama | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| NLPClaim | Feedback | Math | NLPClaim | Feedback | Math | NLPClaim | Feedback | Math | ||
| 23.2/64.6 | 0.9/45.0 | 45.7/18.6 | 26.8/73.2 | 53.4/46.6 | 71.0/21.0 | 14.8/85.2 | 17.5/82.5 | 38.6/25.0 | ||
| 22.0/78.0 | 36.0/44.1 | 43.2/15.6 | 23.2/76.8 | 46.6/53.4 | 69.4/24.2 | 11.1/88.9 | 19.3/78.9 | 31.8/34.1 | ||
| 13.4/86.6 | 74.1/25.9 | 15.7/82.9 | 26.8/73.2 | 55.2/44.8 | 61.3/29.0 | 11.1/88.9 | 17.5/79.8 | 31.8/38.6 | ||
| 38.3/51.7 | 75.9/24.1 | 24.3/57.1 | 24.4/75.6 | 54.3/45.7 | 58.1/27.4 | 11.1/88.9 | 17.5/79.8 | 36.4/36.4 | ||
| 40.2/59.8 | 63.3/36.7 | 20.0/70.0 | 26.8/73.2 | 59.5/40.5 | 54.8/33.9 | 11.1/88.9 | 14.9/83.3 | 38.6/40.9 | ||
| NLPClaim | Feedback | Math | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Config | Gemma | Qwen | Llama | Gemma | Qwen | Llama | Gemma | Qwen | Llama |
| 28.0 / 68.3 | 36.1 / 63.9 | 16.1 / 83.9 | 71.6 / 20.7 | 43.6 / 50.3 | 10.5 / 89.5 | 14.3 / 60.0 | 63.2 / 7.2 | 29.5 / 25.0 | |
| 35.4 / 64.6 | 36.1 / 63.9 | 16.1 / 83.9 | 75.9 / 24.1 | 45.3 / 54.7 | 10.5 / 89.5 | 32.9 / 42.9 | 69.4 / 24.2 | 38.6 / 47.7 | |
| 39.0 / 61.0 | 25.6 / 74.4 | 13.6 / 86.4 | 75.0 / 25.0 | 56.9 / 43.1 | 14.9 / 81.6 | 25.7 / 57.1 | 58.1 / 35.5 | 40.9 / 34.1 | |
| 40.2 / 59.8 | 28.8 / 71.2 | 13.6 / 86.4 | 74.1 / 25.9 | 47.1 / 51.2 | 7.0 / 79.8 | 24.3 / 58.6 | 58.1 / 35.5 | 40.9 / 34.1 | |
| 39.0 / 61.0 | 24.4 / 75.6 | 14.9 / 85.1 | 70.7 / 29.3 | 46.2 / 53.8 | 8.8 / 75.4 | 22.9 / 61.4 | 59.7 / 27.4 | 43.2 / 27.3 | |
| NLPClaim | Feedback | Math | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Config | Gemma | Qwen | Llama | Gemma | Qwen | Llama | Gemma | Qwen | Llama |
| Syc-8 | 24.4 / 74.4 | 50.0 / 50.0 | 30.9 / 65.4 | 43.1 / 56.9 | 68.1 / 31.9 | 19.3 / 80.7 | 57.1 / 14.3 | 62.9 / 27.4 | 45.5 / 15.9 |
| Syc-3 | 51.1 / 43.9 | 41.5 / 58.5 | 29.6 / 66.7 | 60.3 / 38.8 | 56.0 / 44.0 | 27.2 / 72.8 | 47.1 / 18.6 | 69.4 / 19.4 | 38.6 / 15.9 |
| 0-shot | 24.4 / 74.4 | 54.9 / 45.1 | 42.0 / 53.1 | 43.1 / 56.9 | 18.1 / 81.9 | 13.2 / 86.8 | 48.6 / 20.0 | 71.0 / 17.7 | 56.8 / 15.9 |
| Hon-3 | 37.8 / 62.2 | 52.3 / 42.7 | 39.4 / 50.6 | 67.4 / 27.6 | 69.8 / 30.2 | 13.2 / 86.8 | 44.3 / 28.6 | 75.8 / 14.5 | 54.5 / 13.6 |
| Hon-8 | 24.4 / 74.4 | 61.0 / 39.0 | 39.4 / 50.6 | 60.3 / 38.8 | 74.3 / 20.7 | 32.2/62.3 | 48.6 / 20.0 | 75.8 / 14.5 | 54.5 / 13.6 |
| Layer Ablation | Dimension Ablation | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dataset | Gemma | Qwen | Llama | Gemma | Qwen | Llama | |||||||
| Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | ||
| NLPClaim | 0.5 | 0.0 | 0.0 | 24.4 | 75.6 | 18.5 | 79.0 | 2.4 | 93.9 | 25.1 | 62.7 | 19.6 | 79.1 |
| 0.8 | 35.4 | 64.6 | 25.6 | 74.4 | 8.6 | 91.4 | 34.1 | 62.2 | 36.1 | 63.9 | 20.9 | 77.9 | |
| 1.0 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | |
| 1.2 | 37.8 | 62.2 | 25.6 | 74.4 | 12.3 | 86.4 | 39.0 | 61.0 | 28.8 | 71.2 | 18.4 | 81.6 | |
| Only PCA ( only) | Only Residual ( only) | ||||||||||||
| Dataset | Gemma | Qwen | Llama | Gemma | Qwen | Llama | |||||||
| Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | ||
| NLPClaim | 0.5 | 13.4 | 86.6 | 25.6 | 74.4 | 20.9 | 77.9 | 23.2 | 50.0 | 19.0 | 77.3 | 13.6 | 86.4 |
| 0.8 | 31.7 | 68.3 | 25.6 | 74.4 | 17.2 | 81.6 | 52.4 | 47.6 | 33.7 | 66.3 | 13.6 | 86.4 | |
| 1.2 | 45.1 | 54.9 | 23.2 | 76.8 | 13.6 | 86.4 | 37.8 | 62.2 | 26.3 | 73.7 | 13.6 | 86.4 | |
| 1.5 | 35.4 | 64.6 | 24.4 | 75.6 | 20.9 | 71.7 | 19.5 | 80.5 | 28.8 | 71.2 | 13.6 | 86.4 | |
| ( , ) | ( , ) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dataset | Gemma | Qwen | Llama | Gemma | Qwen | Llama | |||||||
| Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | ||
| NLPClaim | 0.5 | 39.0 | 51.2 | 28.0 | 72.0 | 11.1 | 88.9 | 34.1 | 65.9 | 28.0 | 72.0 | 11.1 | 88.9 |
| 0.8 | 37.8 | 62.2 | 28.0 | 72.0 | 11.1 | 88.9 | 32.9 | 67.1 | 28.0 | 72.0 | 11.1 | 88.9 | |
| 1.0 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | |
| 1.2 | 37.8 | 62.2 | 24.4 | 75.6 | 13.6 | 86.4 | 37.8 | 62.2 | 24.4 | 75.6 | 12.3 | 87.7 | |
| ( , ) | ( , ) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dataset | Gemma | Qwen | Llama | Gemma | Qwen | Llama | |||||||
| Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | Hon | Syc | ||
| NLPClaim | 0.5 | 39.0 | 57.3 | 28.0 | 72.0 | 11.1 | 87.7 | 42.7 | 57.3 | 28.0 | 72.0 | 9.9 | 90.1 |
| 0.8 | 31.7 | 68.3 | 28.0 | 72.0 | 11.1 | 88.9 | 26.8 | 73.2 | 28.0 | 72.0 | 11.1 | 88.9 | |
| 1.0 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | 39.0 | 61.0 | 25.6 | 74.4 | 13.6 | 86.4 | |
| 1.2 | 40.2 | 59.8 | 24.4 | 75.6 | 12.3 | 87.7 | 42.7 | 57.3 | 24.4 | 75.6 | 13.6 | 85.2 | |
| Model | Positive Direction (Analytical / Assertive) | Negative Direction (Compliant / Low-frequency) |
|---|---|---|
| Gemma | Reasoning: legitimate, arguably, instead, rather | Technical: MockMvc, RegressionTest, ArgsConstructor, AppModule |
| Quality: professional, systematic, properly, optimized | Hedging: seriousness, discouraging, Toxic, toxicity | |
| Positive affect: pleasantly, happily, sunny, breezy, smooth | ||
| Llama | Reasoning: reasoning, justification, rationale, deliberate | Technical: .DropDown, .Serial, .Currency, RecognitionException |
| Precision: appropriately, formally, exclusively, explicitly | Limiting: alone, only, solely, single, sole | |
| Scope: everything, all, both, choice, cognitive |
| Gemma | Qwen | Llama | |
|---|---|---|---|
| 0.5 | 66.7 / 33.3 | 57.9 / 42.1 | 52.6 / 47.4 |
| 0.8 | 70.6 / 29.4 | 73.7 / 26.3 | 54.5 / 45.5 |
| 1.0 | 88.2 / 11.8 | 75.0 / 25.0 | 50.0 / 50.0 |
| 1.2 | 81.8 / 18.2 | 81.0 / 19.0 | 59.1 / 40.9 |
| 1.5 | 88.9 / 11.1 | 81.2 / 18.8 | 61.9 / 38.1 |
| 1.8 | 88.9 / 11.1 | 87.0 / 13.0 | 60.0 / 40.0 |
| Gemma | Qwen | Llama | |
|---|---|---|---|
| 0.5 | 39.1 / 60.9 | 75.0 / 12.5 | 22.2 / 77.8 |
| 0.8 | 46.2 / 53.8 | 63.3 / 36.7 | 24.1 / 75.9 |
| 1.0 | 48.1 / 51.8 | 80.0 / 20.0 | 30.0 / 70.0 |
| 1.2 | 50.0 / 50.0 | 86.7 / 13.3 | 30.0 / 70.0 |
| 1.5 | 50.0 / 50.0 | 100.0 / 0.0 | 36.7 / 63.3 |
| 1.8 | 53.6 / 46.4 | 100.0 / 0.0 | 41.7 / 58.3 |
LLM Sycophancy
Large language model sycophancy is the tendency to mirror users’ beliefs, preferences, or authority cues at the expense of independent judgment.
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