Extend builds document processing on large language models, extracting structure from the messy paperwork enterprises actually run on, and posts a Forward Deployed Engineer role in New York. Worth disambiguating: this is the Y Combinator document-extraction Extend, not the product-protection and warranty company of the same name, which does not hire for this function.
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The Extend Forward Deployed Engineer interview process
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Compiled from our research and publicly available information (candidate reports and company interview guides). Interview loops change and are continuously iterated, and they vary by team, level, and region. Treat this as directional preparation, not an official spec, and confirm the exact rounds with your recruiter or hiring point of contact.
Extend Forward Deployed Engineer salary
What we can trace, labelled by where it came from. We publish a band only where there is a source behind it, so some of this page is a gap rather than a number.
We do not have a verified compensation band for this role at Extend recorded in this profile. Check the current posting for the role, level and location before comparing offers. Their careers page is the authority, and postings in some jurisdictions are required to state a range.
A US or EU AI company with no large India engineering centre. An India-based hire here is usually a global-remote contract, often USD-denominated, which is the highest-paying route into the role from India and also the hardest to get.
Reported range for this type of employer, not a figure reported for this company. Whether an India-based hire is possible at all depends on their entity and visa position, so check their careers page before you plan around it.
Full method, US bands by level, and the three India tiers side by side are in the FDE salary guide, including what actually moves your number between these tiers.
Representative Forward Deployed Engineer questions for Extend's loop
Extend's loop draws from these tracks. Here are the highest-signal questions in each, ordered by what candidates rate most useful.
Go deeper on the topics Extend's loop tests
The tracks that map to a Extend Forward Deployed Engineer loop, ordered easy to hard.
The concepts Extend's Forward Deployed Engineer loop assumes you know
The vocabulary and mental models behind Extend's questions, from our curriculum. Start with the foundations free; the deeper, interview-defining ideas are part of premium.
RETRIEVAL & AGENTS
FoundationalRetrieval-Augmented Generation (RAG)RAG grounds a language model in your own data by retrieving relevant passages at query time and putting them in the prompt, so the model answers from real sources instead of memory. It is the default pattern for almost every enterprise FDE deployment, which is why nearly every loop tests it.
FoundationalVector DatabasesA vector database stores embeddings alongside metadata and answers nearest-neighbor queries fast using approximate indexes. The real interview question is not how they work but when you actually need one instead of a library or plain Postgres with pgvector.
CoreSign inHybrid Search (Lexical + Vector)Hybrid search runs a keyword retriever (BM25) and a dense vector retriever side by side, then merges their result lists, because each one misses cases the other catches. Vectors lose exact codes and rare jargon, BM25 loses paraphrase, and combining them with Reciprocal Rank Fusion usually beats either alone.
Advanced🔒 PremiumAgent MemoryAgent memory is how an agent carries state across turns and sessions. Short-term memory is the conversation and scratchpad living inside the context window, bounded and expensive. Long-term memory is an external store the agent writes to and retrieves from on demand, usually via RAG, so it can recall facts from last week without holding them in the prompt. FDE loops probe this because the hard parts, summarization, what to persist, and stale or contradictory memory, are where agents quietly break.
FOUNDATIONS OF LLMS & GENAI
FoundationalTokenization & TokensA language model does not read characters or words. It reads tokens: sub-word chunks produced by a tokenizer, each mapped to an integer the model embeds. Tokens are the unit of the context window and of billing, and the way text splits into them explains a surprising number of model quirks, which is why almost every loop opens here.
FoundationalThe Context WindowThe context window is the fixed number of tokens a language model can attend to at once, and input and output share that same budget. Understanding it is what separates engineers who can size a prompt, control cost and latency, and decide when to reach for RAG from those who just paste everything in and hope.
FoundationalEmbeddings & Vector RepresentationsAn embedding turns a piece of text into a list of numbers positioned so that similar meanings land near each other in space, which lets you search by meaning instead of by keyword. Embeddings are the engine under RAG, semantic search, clustering, and deduplication, so FDE loops expect you to explain cosine similarity and the pitfalls that quietly break a vector index.
Advanced🔒 PremiumLoRA and Parameter-Efficient Fine-tuningFull fine-tuning updates every weight in a model, which is expensive to train and produces a full-size checkpoint per task. LoRA freezes the base model and trains small low-rank adapter matrices instead, giving tiny swappable checkpoints; QLoRA adds a quantized frozen base so the whole thing fits on a single GPU. FDE loops probe it because it is how you adapt a model on a customer's data without their budget or their hardware blowing up.
EVALUATION & ML FOUNDATIONS
CoreSign inInformation Theory for ML: Entropy, Cross-Entropy, KL and PerplexityFour quantities from information theory keep showing up in ML: entropy measures the average surprise in a distribution, cross-entropy is the loss that trains classifiers and language models, KL divergence measures how far one distribution sits from another, and perplexity is the intuitive branching-factor view of a language model's loss. Knowing where each appears separates people who tuned a loss function from people who only imported one.
FoundationalPrecision, Recall and F1Precision asks how many of your positive predictions were right; recall asks how many of the real positives you caught. They trade off against each other, F1 is their harmonic mean, and accuracy lies to you the moment the classes are imbalanced.
FoundationalGradient Descent & Learning RateGradient descent is how almost every model learns: compute the slope of the loss with respect to the weights, then step the weights a little in the downhill direction. The learning rate sets the step size, and it is the single most consequential knob. Too small and training crawls; too large and it overshoots and diverges.
Advanced🔒 PremiumOffline vs Online EvaluationOffline evaluation scores a change against a fixed golden set: fast, cheap, repeatable, and runnable in CI before anything ships. Online evaluation measures the change on real traffic and real users, usually via A/B, and is the only true read on impact. The two are not interchangeable: offline gains routinely fail to hold online because of distribution shift and metric gaming. The discipline FDE loops test is using offline to gate and online to confirm.
THE CUSTOMER-FACING CRAFT
FoundationalRequirements DiscoveryRequirements discovery is the work of finding the real problem hiding behind the customer's stated ask. The request they hand you ("build us a chatbot") is almost never the need; the FDE who surfaces who uses it, what success looks like, what data actually exists, and why the deadline is the deadline is the one who ships something people use.
FoundationalScoping Ambiguous ProblemsScoping an open-ended prompt ("a city wants to reduce 911 response times") is a structured move, not a flash of inspiration: clarify inputs and constraints, state your assumptions out loud, carve out the smallest useful MVP, name the accuracy/cost/latency trade-offs you are choosing, and plan for what happens when it fails. Diving straight into a model or an architecture is the most common reason candidates get cut in the simulation round.
FoundationalExplaining Trade-offs to Non-EngineersAn exec does not care whether you chose RAG or fine-tuning; they care what it costs, when it ships, and what it might get wrong. Translating a technical trade-off means converting accuracy, cost, and latency into the decision the business is actually making, framing each option as a choice with a consequence in their terms, and answering the question they will all eventually ask: why does the AI give a different answer every time, and why is that not a bug.
Advanced🔒 PremiumPilot Acceptance CriteriaPilot acceptance criteria connect a test result to a bounded deployment decision. Define eligible work, failure limits, missing evidence and the people who can approve the next step.
Where to apply, and official Extend resources
Straight from Extend: open roles and the company's own hiring guidance. Prep here, then apply there.
External links to Extend's own pages. Roles and processes change; always confirm on the official site.
Yes. The document-extraction Extend, a Y Combinator company, posts a Forward Deployed Engineer role in New York on its own Ashby board. The warranty company also called Extend does not hire for this role.
Take a customer's real document set, which is rarely as clean as a demo, and make extraction reliable against it. The work is evaluation-heavy: knowing whether the pipeline is right on documents nobody has labelled is most of the job.
We have no confirmed public breakdown of the loop. Given the product, prepare document-processing and extraction reasoning, how you evaluate accuracy without ground truth, and the customer-facing rounds an embedded role tests.
Extend does not publish a band we can confirm for this role. It is an early-stage New York company, so expect base plus a meaningful equity component.
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