About the job
We're hiring a Research Engineer to advance the science and engineering that goes into making Claude this trustworthy searcher. This is a research role for someone who is unusually rigorous: you'll define hypotheses about what makes a model an epistemically sound searcher, design the experiments that test them, and turn search post-training from a craft into a measurable science.
Responsibilities
Own a research direction for a class of search post-training problems end-to-end: form hypotheses about latent capabilities, design experiments that isolate them, run training, and decide what to try next.
Build the instrumentation that turns environment design into a controlled experiment so we can study how each environment factor contributes to the capabilities we care about, rather than overfitting to any one regime.
Design frontier-discriminating evaluations that distinguish genuine reasoning over evidence from plausible pattern matching and that hold up as models improve.
Drive optimization rigor across the stack: efficient experiment design, ablations, training run economics, and the discipline to know when a result is real.
Collaborate deeply with researchers across post-training, RL infrastructure, and product to translate model behavior in the wild into concrete training signals and back again.
Set the bar for the team's experimental standards — what we measure, how we measure it, how we know a result is real.
Qualifications
Minimum
Have an unusually rigorous, quantitative mindset
Are an outstanding software engineer in Python, comfortable across the stack from data pipelines to RL training to evaluation infrastructure
Have shipped real ML research repeatedly, with taste for which experiments are worth running.
You instinctively reach for ablations, controls, and confidence intervals to understand why
Operate well with high autonomy and ambiguity and can identify the most impactful problem to work on next without being told
Want to set research direction, advocate for experimental rigor, and raise the bar for the people around you
Communicate research clearly in writing and in person; you can defend a design choice and update on evidence
Preferred
Hands-on experience with RL on large language models — environments, reward design, training stability, scaling behavior.
Background in search, retrieval, RAG, or agents that reason over external information sources.
Experience building evaluations for open-ended or knowledge-intensive LLM behavior
Prior work in a research-heavy environment — frontier AI lab, quant research firm, or similarly demanding empirical setting — where rigor is the default.
Published research on LLMs, RL, retrieval, calibration, or related topics.
Experience with distributed training systems and large-scale experimentation infrastructure.