Neel Nanda - Mechanistic Interpretability (Sparse Autoencoders)

Machine Learning Street Talk (MLST)

Neel Nanda, a senior research scientist at Google DeepMind, leads their mechanistic interpretability team. In this extensive interview, he discusses his work trying to understand how neural networks function internally. At just 25 years old, Nanda has quickly become a prominent voice in AI research after completing his pure mathematics degree at Cambridge in 2020.

Nanda reckons that machine learning is unique because we create neural networks that can perform impressive tasks (like complex reasoning and software engineering) without understanding how they work internally. He compares this to having computer programs that can do things no human programmer knows how to write. His work focuses on "mechanistic interpretability" - attempting to uncover and understand the internal structures and algorithms that emerge within these networks.

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SHOWNOTES, TRANSCRIPT, ALL REFERENCES (DONT MISS!):

https://www.dropbox.com/scl/fi/36dvtfl3v3p56hbi30im7/NeelShow.pdf?rlkey=pq8t7lyv2z60knlifyy17jdtx&st=kiutudhc&dl=0

We riff on:

* How neural networks develop meaningful internal representations beyond simple pattern matching

* The effectiveness of chain-of-thought prompting and why it improves model performance

* The importance of hands-on coding over extensive paper reading for new researchers

* His journey from Cambridge to working with Chris Olah at Anthropic and eventually Google DeepMind

* The role of mechanistic interpretability in AI safety

NEEL NANDA:

https://www.neelnanda.io/

https://scholar.google.com/citations?user=GLnX3MkAAAAJ&hl=en

https://x.com/NeelNanda5

Interviewer - Tim Scarfe

TOC:

1. Part 1: Introduction

[00:00:00] 1.1 Introduction and Core Concepts Overview

2. Part 2: Outside Interview

[00:06:45] 2.1 Mechanistic Interpretability Foundations

3. Part 3: Main Interview

[00:32:52] 3.1 Mechanistic Interpretability

4. Neural Architecture and Circuits

[01:00:31] 4.1 Biological Evolution Parallels

[01:04:03] 4.2 Universal Circuit Patterns and Induction Heads

[01:11:07] 4.3 Entity Detection and Knowledge Boundaries

[01:14:26] 4.4 Mechanistic Interpretability and Activation Patching

5. Model Behavior Analysis

[01:30:00] 5.1 Golden Gate Claude Experiment and Feature Amplification

[01:33:27] 5.2 Model Personas and RLHF Behavior Modification

[01:36:28] 5.3 Steering Vectors and Linear Representations

[01:40:00] 5.4 Hallucinations and Model Uncertainty

6. Sparse Autoencoder Architecture

[01:44:54] 6.1 Architecture and Mathematical Foundations

[02:22:03] 6.2 Core Challenges and Solutions

[02:32:04] 6.3 Advanced Activation Functions and Top-k Implementations

[02:34:41] 6.4 Research Applications in Transformer Circuit Analysis

7. Feature Learning and Scaling

[02:48:02] 7.1 Autoencoder Feature Learning and Width Parameters

[03:02:46] 7.2 Scaling Laws and Training Stability

[03:11:00] 7.3 Feature Identification and Bias Correction

[03:19:52] 7.4 Training Dynamics Analysis Methods

8. Engineering Implementation

[03:23:48] 8.1 Scale and Infrastructure Requirements

[03:25:20] 8.2 Computational Requirements and Storage

[03:35:22] 8.3 Chain-of-Thought Reasoning Implementation

[03:37:15] 8.4 Latent Structure Inference in Language Models