| name | interpretability-nav |
| description | Navigate mechanistic interpretability concepts, tools, and SAE architectures. Quick reference for SAE variants, feature steering methods, circuit discovery, and trust calibration. |
| triggers | ["interpretability","SAE","sparse autoencoder","mechanistic interpretability","feature steering","refusal circuit","circuit discovery","ACDC","attribution patching","causal scrubbing","ActAdd","activation steering","RepE","trust calibration","sycophancy","TopK SAE","Gated SAE"] |
Mechanistic Interpretability Navigator
3-Layer Tool Chain
Layer 1: SAE → decompose activations → features → interpretable units
Layer 2: Circuit Discovery → connect features → circuits → behavior mechanisms
Layer 3: Feature Steering → manipulate features → control behavior → applications
SAE 3 Generations
| Gen | Architecture | L0 Control | Dead Features | Absorption | Shrinkage | 2025 Rec |
|---|
| Standard | h=ReLU(W_enc*x+b) | Indirect(λ) | Yes | Yes | Yes | Baseline |
| Gated | gate=ReLU(W_gatex), mag=ReLU(W_magx), h=gate*mag | Better | Reduced | Reduced | No | Frontier |
| TopK | h=TopK(W_enc*x+b, K) | Exact=K | None | None | No | ✓ Best |
Key Math
- Standard: L = ||x-x̂||² + λ||h||₁
- Gated: L = ||x-x̂||² + λ||gate||₁ (magnitude NOT penalized!)
- TopK: L0=K per token (exact control, no L1 needed)
RTX 4090 Implementation
- 7B INT4 residual stream dim=4096
- SAE features=16x→65,536 per layer
- TopK L0=50-100 per token
- TransformerLens → hook-based activation extraction
- Training ~2-4h estimated on RTX 4090
- Simulator:
tools/sae_simulator.py
Feature Steering 5 Methods
| Method | Approach | Stability | Complexity | Production |
|---|
| ActAdd | s=a⁺-a⁻ contrastive difference | Low(brittle) | Lowest | Research |
| CAA | Average N contrastive pairs | Medium | Low | Research |
| RepE | PCA directions + multi-layer | Good | Medium | Possible |
| DiffSteer | Functional/task-specific | Good | Medium | Frontier |
| LoRA-Steer | Learned low-rank adapter | ✓Best | High | ✓ Production |
Circuit Discovery 3-Layer Pipeline
ACDC (auto prune edges) → Attribution Patching (gradient 100x faster) → Causal Scrubbing (strict verification)
Fast screening → Approximate refinement → Gold-standard confirmation
Refusal Circuit
Harmful request → detection_features → intermediate_features → suppress_output → "I cannot help"
Dual-use: transparency vs security tension. Publishing refusal circuit details helps adversaries bypass safety.
Trust Calibration
- Overtrust: user trusts AI when it shouldn't → error propagation
- Undertrust: user doesn't trust AI when it should → efficiency loss
- Calibrated: appropriate trust matching AI capability → optimal
- Conversational framing increases 30-40% perceived competence → overtrust accelerator
- Simulator:
tools/trust_calibration_simulator.py
Key Notes
notebook/fundamentals/mechanistic-interpretability-deep-dive.md — comprehensive theory
notebook/fundamentals/ai-safety-guardrails-production-deep-dive.md — Defense-in-Depth connection
notebook/fundamentals/ai-economic-impact-human-ai-interaction-deep-dive.md — trust/sycophancy/anthropomorphism
Key Tools
- TransformerLens (neel nanda) — activation extraction + hooks
- steering-vectors — ActAdd for HuggingFace models
- ACDC (TransformerLensOrg) — automated circuit discovery
- Neuron Viewer (Anthropic) — SAE feature visualization