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Exelixis Software Engineer Interview Guide

Exelixis Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at Exelixis plays a pivotal role in bridging the gap between cutting-edge biotechnology and robust technical infrastructure. You are tasked with building and maintaining the systems that enable our scientific teams to accelerate the discovery and development of transformative cancer therapies. Your work directly impacts the efficiency of our research pipelines, requiring a high degree of technical precision and a commitment to operational excellence. This role is both challenging and strategically significant. You will be responsible for navigating complex, high-stakes environments where your contributions directly support the company's mission to deliver innovative, effective treatments to patients.

This guide is scoped to a Software Engineer candidate at Exelixis.

Focus areas

  • DevSecOps
  • Packaging Systems / Build Packaging
  • Security Engineering Practices

The Exelixis interview process

Exelixis candidates report 2 rounds over 2-4 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

Non-technical screening conducted by a manager to verify professional background and alignment with company needs.

What to demonstrate

  • Non-technical screening conducted by a manager to verify professional background and alignment with company needs
  • Depth in DevSecOps

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Onsite Interview

Rigorous assessment of technical capabilities in a live setting, focusing on practical demonstration of skills.

What to demonstrate

  • Rigorous assessment of technical capabilities in a live setting
  • Focusing on practical demonstration of skills

How to prepare

  • Answer aloud and timed: Explain the specific command-line steps you would take to troubleshoot a latency issue in a production environment.
  • Answer aloud and timed: When faced with a discrepancy between your experience and a provided job description, how do you bridge that gap during a live technical discussion?

Where candidates lose points

Own your resume

You will be asked about every detail on your CV. Be prepared to provide specific examples for every skill or project you have listed.

Maintain composure

If an interviewer challenges your answer, stay calm. Acknowledge the question, provide your reasoning, and remain professional.

Focus on precision

Avoid vague answers. When asked about a technical process, provide clear, step-by-step details rather than general summaries.

Prepare for historical questions

Be ready to discuss technical details from projects you completed several years ago. Review your past work thoroughly before the interview.

Questions & practice

How do you approach a situation where your infrastructure knowledge is challenged by a platform you are less f

Medium · Problem Solving and Adaptability

How do you approach a situation where your infrastructure knowledge is challenged by a platform you are less familiar with?

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

When you encounter a technical roadblock that is outside of your immediate scope, what is your methodology for

Medium · Problem Solving and Adaptability

When you encounter a technical roadblock that is outside of your immediate scope, what is your methodology for finding a resolution?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

How do you manage your workflow when tasked with multiple, high-priority engineering requests simultaneously?

Medium · Problem Solving and Adaptability

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

  1. One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
  2. Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
  3. State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
  4. Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

  • A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
  • Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Denormalise tenant onto revisions and backfill it live

Hard · denormalisation · online migration · backfill

resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.

Approach

  1. Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
  2. Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
  3. Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
  4. Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.

Follow-up

  • The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
  • How do you verify the backfill actually finished, given rows are still being inserted while it runs?

Can you walk us through a specific project from the last ten years that demonstrates your proficiency in this

Medium · Technical Depth and Proficiency

Can you walk us through a specific project from the last ten years that demonstrates your proficiency in this stack?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe your process for maintaining security protocols within a CI/CD pipeline.

Medium · Technical Depth and Proficiency

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the specific command-line steps you would take to troubleshoot a latency issue in a production environ

Medium · Technical Depth and Proficiency

Explain the specific command-line steps you would take to troubleshoot a latency issue in a production environment.

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Exelixis candidates report.

Day 1 — Map the Exelixis loop

  • Write out the reported sequence: Initial Screening, Onsite Interview.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 2 reported rounds, with the weakest marked.

Day 2 — Work DevSecOps

  • Spend the session on DevSecOps, which Exelixis candidates report being tested on.
  • Write one worked example in DevSecOps and time yourself on it.

Deliverable: One timed worked example in DevSecOps.

Day 3 — Work Packaging Systems / Build Packaging

  • Spend the session on Packaging Systems / Build Packaging, which Exelixis candidates report being tested on.
  • Write one worked example in Packaging Systems / Build Packaging and time yourself on it.

Deliverable: One timed worked example in Packaging Systems / Build Packaging.

Day 4 — Work Security Engineering Practices

  • Spend the session on Security Engineering Practices, which Exelixis candidates report being tested on.
  • Write one worked example in Security Engineering Practices and time yourself on it.

Deliverable: One timed worked example in Security Engineering Practices.

Day 5 — Answer out loud: Technical Depth and Proficiency

  • Answer aloud, timed: Can you walk us through a specific project from the last ten years that demonstrates your proficiency in this stack?
  • Answer aloud, timed: How do you handle configuration management when working with cloud-native architectures?

Deliverable: Spoken answers to 2 reported Technical Depth and Proficiency question(s), under time.

Day 6 — Answer out loud: Problem Solving and Adaptability

  • Answer aloud, timed: How do you approach a situation where your infrastructure knowledge is challenged by a platform you are less familiar with?
  • Answer aloud, timed: Describe a time you had to pivot your technical strategy mid-project due to changing business requirements.

Deliverable: Spoken answers to 2 reported Problem Solving and Adaptability question(s), under time.

Day 7 — Dry run for Exelixis

  • Run one full mock under time, then write down the two questions you most want to ask your interviewers.

Deliverable: A completed timed mock and two questions to ask.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

How do you handle configuration management when working with cloud-native architectures?

Medium · Technical Depth and Proficiency

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

When faced with a discrepancy between your experience and a provided job description, how do you bridge that g

Medium · Technical Depth and Proficiency

When faced with a discrepancy between your experience and a provided job description, how do you bridge that gap during a live technical discussion?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a time you had to pivot your technical strategy mid-project due to changing business requirements.

Medium · Problem Solving and Adaptability

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?