Two Refusals or One? Disentangling Safety and Epistemic Abstention Directions in Language Model Activations

Instruction-tuned language models show two refusal-like behaviors that look similar at the surface: safety refusal (declining harmful requests) and epistemic abstention (declining to answer when the model lacks enough knowledge). Prior work has found a low-dimensional safety-refusal direction in residual stream activations, and ablating that direction can remove refusal behavior. But we don't know whether epistemic abstention uses the same geometric handle. We extract both directions with difference-in-means on contrastive prompt pairs, then compare them across every layer of Llama-3.1-8B-Instruct. Next, we run activation-space cross-ablation: remove one direction, vary the intervention strength and target layers, and check whether the other behavior breaks. We also measure NF4/INT8 quantization drift, train a linear probe on epistemic activations, and run bounded replication probes on Qwen3-8B and Gemma-2-9B-Instruct. The two directions are geometrically distinct in Llama: mean cosine across layers is $0.049$, the maximum cosine is only $0.183$, and the top safety and epistemic layers occur at different depths. In the strongest safety ablation setting we identify, safety refusal drops from $0.98$ to $0.16$. Epistemic abstention doesn't collapse; it moves from $0.82$ to $0.88$ (the bootstrap 95% CI for cross-contamination spans zero, so the shift is not statistically significant). A simple held-out linear probe on epistemic activations reaches $1.00$ accuracy at the selected layer, which suggests the feature is linearly real even though directional ablation remains weak. Quantization mostly preserves the geometry: NF4 maintains cosine $0.994$ for the safety direction and $0.978$ for the epistemic direction relative to FP16. Qwen3-8B and Gemma-2-9B-Instruct show the same qualitative separation, with cosine $-0.039$ and $0.123$ at their top safety layers. These results point to a simple conclusion: safety refusal and epistemic abstention are not mediated by the same dominant activation-space direction.