Selected work — 2026

01 / 05

I reverse-engineer what large models actually compute, then use that to make them cheaper, safer, and easier to check.

Focus

Three questions I keep returning to.

01

Mechanistic interpretability

Reverse-engineering the circuits inside transformers. Sparse autoencoders, causal tracing, activation patching — anything that turns a black box into a wiring diagram.

  • SAE
  • Causal tracing
  • Circuits

02

Scaling & efficiency

How capability changes with compute, data, and sparsity. Which parameters you can remove before the model notices, and which you absolutely cannot.

  • Scaling laws
  • MoE
  • Distillation

03

Evaluation

Benchmarks that survive contamination. Tests for reasoning, honesty, and refusal that keep their meaning after the leaderboard is gamed.

  • Contamination
  • Refusal
  • Reasoning

Selected work

Four projects, 2024 — 2026.

01SIFTSparse feature tracing at 70B parametersInterpretabilitySAEOpen source2026

A feature-level tracer that runs on a single eight-GPU node. It attributes refusal behaviour in a 70B model to a small set of sparse features, without retraining the model or touching its weights.

PyTorch · CUDA · 8×H100

4.1%
of features carry 88% of the causal effect on refusal
7.3x
less GPU memory than the reference tracing pipeline
11
downstream labs adopted the release in six months
02ATLAS-9A 9B multilingual reasoning modelPretrainingMultilingualReasoning2025

Trained from scratch on 1.2T tokens across 23 languages. Most of the gain came from data mixing and a curriculum on chain-of-thought traces, not from adding parameters.

Megatron · BF16 · 128×H100

+14.6
points on MMLU-Pro over a 13B baseline
23
languages above the 60% pass mark
1.2T
tokens, 41 days on 128 GPUs
03CIRCUIT BENCH240 hand-built tasks for interpretability claimsBenchmarkInterpretabilityEvaluation2025

A diagnostic suite that checks whether an interpretability method actually recovers a known circuit. Every task has a ground-truth mechanism, so a plausible-looking explanation can be scored as wrong.

Python · TransformerLens · 18 checkpoints

240
tasks across 6 architectural families
18
models, from 1B to 70B parameters
0.31
mean score for random probes — below chance
04PRISMMultimodal retrieval without a second encoderMultimodalRetrievalInfrastructure2024

A retrieval layer that reuses a frozen vision encoder and a small adapter instead of training a joint embedding from scratch. Same recall, a fraction of the compute.

CLIP · FAISS · Rust service

3.4×
faster indexing than the joint-embedding baseline
96.2%
recall@10 on the internal image-text set
1
adapter, 38M parameters, frozen backbone

Publications

* equal contribution. Selected, not exhaustive.

2026

Sparse Features Are Not Enough: Causal Sufficiency in SAE Explanations

H. Lu, M. Okafor, J. Ren

NeurIPS 2026Under review

2025

Contamination-Resistant Evaluation for Code Models

H. Lu*, T. Weiss, A. Duarte

ICML 2025Oral

2025

Circuit Bench: A Diagnostic Suite for Mechanistic Claims

H. Lu, S. Kaur, L. Feng, M. Okafor

ICLR 2025Spotlight

2024

Scaling Laws for Sparse Mixture Models Under Fixed Compute

H. Lu, A. Duarte

TMLR 2024Journal

2024

What Refusal Looks Like Inside a Transformer

H. Lu*, J. Ren, P. Sandoval

ACL 2024Long paper

About

Short version.

I am a research scientist working on the gap between what a model can do and what we can explain about it. Most of my work starts with a benchmark that someone has learned to game, or a circuit diagram that nobody has verified.

Before this I spent four years on a PhD in computational neuroscience, which is where I picked up the habit of measuring before theorising. I still write code every day.

2026 —

Research Scientist

Institute for Computational Intelligence

Interpretability and evaluation for frontier-scale models.

2024 — 2026

Postdoctoral Researcher

Frontier Lab, Zurich

Sparse feature tracing; built the lab's first eval harness.

2020 — 2024

PhD, Computational Neuroscience

ETH Zürich

Thesis on causal methods for reading neural representations.

2019 — 2020

Research Intern

Vision Group, Tsinghua

Multimodal retrieval and dataset construction.

14

Peer-reviewed papers

1.9k

Citations

06

Open-source releases

08

Years in research