Paper reading rounds don't test whether you memorized a paper's conclusion — they test whether you can break down an unfamiliar paper's problem, method, and limitations in 15-20 minutes and ask a meaningful follow-up question. Today's paper introduces invalidation contracts: attaching version stamps and cacheability hints to cached LLM-agent error-recovery suggestions, so that when server-side data drifts, the client can evict exactly the stale entries at row-level granularity instead of discarding everything or re-deriving from scratch every time. The paper's core insight is decomposing 'did this caching mechanism actually save money' into two independent variables — validity (whether the cached content is still correct, determined purely by protocol design) and compliance (whether the planner model actually adopts the suggestion on the first try, which is model-dependent: the same wire bytes get 100% first-try compliance on Claude Haiku 4.5 but can drop below 11% on Claude Sonnet 5). That decomposition itself is great interview material — it demonstrates how to split a vague performance question into two separately measurable, separately attributable factors.
ML coding interviews don't test whether you've memorized LeetCode templates — they test whether you can hand-write building blocks in NumPy (linear layers, residual connections, layer norm, causal self-attention) and read someone else's training/inference loop well enough to find the bug. Today covers four concepts: the real test in ML coding interviews is hand-implementation, not memorized answers; BPE tokenizer's core logic is 'count frequencies, merge iteratively, encode using the exact same merge order learned during training' — get the order wrong and encode no longer matches decode; batch inference trade-offs throughput against latency and has to handle padding waste across variable-length sequences; and the test for whether to vectorize a loop in NumPy is whether it has cross-element dependencies. The practice problem is a real technical-screen question from Glean — implementing a BPE tokenizer end to end, from training to encode/decode.
LLM & Agent Engineering interviews don't test whether you can wire up LangChain — they test whether you can turn a vague 'something's broken' into a set of testable sub-hypotheses. Today covers four high-frequency concepts: why RAG's 'retrieval is right but the answer is wrong' gap needs retrieval and generation evaluated as two separate systems; why a bigger agent context window doesn't fix quality decay, because the real problem is context pollution (noise diluting attention) rather than too few tokens; the decision logic between RAG and fine-tuning — 'RAG owns knowledge, fine-tuning owns behavior'; and why LLM-as-judge carries consistency and self-preference bias and can't stand alone as the only metric. The practice problem is a common enterprise scenario question — retrieval accuracy is 90% but answer accuracy is only 60%, how do you diagnose it — walking through how to turn a vague symptom into verifiable hypotheses.
ML System Design interviews don't test whether you can draw an architecture diagram — they test whether you can articulate the trade-offs at every layer. Today covers four high-frequency topics: how a feature store guarantees training/serving consistency, how to sequence deployment strategies with automated rollback triggers, why monitoring needs to split into system/data/model layers with PSI/KS tests for drift, and how to budget latency for online inference down to the millisecond. The practice problem is 'design a real-time e-commerce recommendation service,' walking through requirement clarification, scale estimation, feature store design, and deployment strategy end to end.
Deep Learning & NLP interviews don't test whether you can draw a transformer diagram — they test whether you understand what each design decision trades away. Today covers four high-frequency topics: how self-attention computes and what KV cache saves, the vocab-size trade-off in tokenization, the senior-candidate detail that 'an embedding is a vector-space contract, and matching dimensions doesn't mean compatible,' and how to choose between fine-tuning and prompting while guarding against catastrophic forgetting. The practice problem is Scale AI's 'design an embedding and classification API,' walking through version compatibility, partial failure, and multi-tenant isolation end to end.
ML fundamentals interviews test whether you can diagnose the gap between 'the metric looks great' and 'production is on fire.' Today covers four high-frequency topics: why AUC-ROC inflates under heavy class imbalance, why cross-entropy beats MSE for classification (it comes down to vanishing gradients), whether bagging or boosting fixes variance versus bias, and the common misconception that multicollinearity hurts prediction — it only hurts interpretability.
A behavioral interview isn't testing whether you have a story — it's testing whether you can turn a technical incident into a narrative with a clear situation, concrete actions, and quantified results in 90 seconds. Today walks through a full STAR answer for the AI Engineer classic — 'a deployed model's performance suddenly collapsed, how did you fix it under cross-team pressure' — and reviews what got practiced this week across the five topics from ML Fundamentals through Paper Reading.
A paper reading round doesn't test whether you finished the paper — it tests whether you can identify the core claim within a limited window, articulate the trade-offs behind its design choices, and raise a verifiable follow-up question. Today we use the newly published SparseRead (a token-efficient reading layer, posted to arXiv on 2026-08-23) as practice material, dissecting its regime-aware Read Gate, Reader Backends, and stateful protocol, then running a full round of 'pre-filter vs. post-hoc pruning' follow-up questions.
2026 ML coding rounds no longer just test 'can you build it from scratch' — they also test whether you can read code someone else broke. Today covers five topics: a state-machine design for LLM inference scheduling, strategies for debugging existing ML code, NumPy shape traps, leakage prevention in pandas time-series features, and computing AUC-ROC by hand. The practice problem is adapted from a recently leaked Anthropic OA: a simplified GPU request scheduler.
AI Engineer interviews in 2026 no longer just ask 'can you build a RAG pipeline' — they test whether you can make defensible tradeoffs under real failure modes. Today covers five topics: when RAG should become agentic RAG, how production context windows are assembled layer by layer and the lost-in-the-middle problem, how guardrails stop malicious input and output, the RLHF reward-model training loop, and how to tell retrieval failure, generation failure, and infinite agent loops apart from a trace.
ML system design interviews test whether you can translate a business goal into a complete ML system — not whether you can recite buzzwords. Today we focus on four high-frequency topics: online/offline feature stores with point-in-time correctness, latency budgets for online inference and shadow mode, choosing the right randomization unit for A/B tests and separating novelty effects, and using PSI to detect data drift vs concept drift.
ML fundamentals interviews don't test whether you can recite definitions — they test whether you can walk through a structured diagnostic when handed a train/val accuracy gap. Today covers four high-frequency topics: bias-variance decomposition and learning curve interpretation, geometric intuition for L1/L2 regularization and when to pick which, aligning loss functions with business objectives instead of accepting defaults, and why AdamW decouples weight decay from L2 regularization.
Behavioral interviews for AI Engineers aren't about listing projects you've worked on — they're about letting the interviewer infer from how you tell the story whether you can handle bigger scope, define problems in ambiguous situations, and honestly say 'here's where I went wrong' when things break. Today's practice uses a story framework around 'your RAG system started giving wrong answers after launch — how did you find the root cause and restore client trust,' followed by a review of this week's ML System Design, Coding, and Paper Reading sessions.
A paper reading round doesn't test whether you finished the paper — it tests whether you can talk about it as if you ran the research yourself: articulating the trade-offs behind key design choices, spotting gaps in the experimental design, and predicting what should come next. Today we use the newly published OneDayAgent (a long-horizon agent harness, posted to arXiv on 2026-08-04) as practice material, dissecting its task decomposition, context compression, and verify-repair mechanisms, then running through a full round of typical follow-up questions.
ML coding rounds don't test leetcode recall — they test whether you can implement attention, k-means, and other ML primitives from scratch using only NumPy, while articulating the shape and complexity at every step. Today covers five high-frequency topics: vectorized thinking, softmax numerical stability, shape tracking and complexity analysis, padding/masking for batch inference, and how to verify correctness when hand-coding algorithms.
The core of ML system design interviews isn't which model to pick — it's how to keep the model alive in production. Today covers four high-frequency topics: online/offline separation in feature stores, root causes and prevention of training-serving skew, deployment strategies (shadow/canary/blue-green), and ML-specific monitoring beyond HTTP error rates.