As a Software Engineer at Zest AI, you will play a pivotal role in developing and maintaining sophisticated machine learning systems that drive the company's innovative lending solutions. Your contributions will directly influence how financial institutions leverage artificial intelligence to enhance credit decision-making processes, thereby improving access to credit for a diverse range of customers. This position is critical to Zest AI's mission of making credit more accessible and fair, as it combines technical expertise with a keen understanding of the financial landscape. You will work alongside talented engineers and data scientists in an environment that fosters collaboration and creativity. Your responsibilities will include designing robust software solutions, implementing algorithms, and refining existing systems to ensure they meet the high standards expected in a competitive market. The complexity of the problems you tackle—ranging from algorithm optimization to system scalability—makes this role not only challenging but also rewarding. You will have the opportunity to contribute to projects that have a tangible impact on users and the business, ensuring that Zest AI continues to lead in the fintech sector.
Phone Screen
reportedInitial screening call with a recruiter to discuss the candidate's background and fit for the role.
What to demonstrate
- Initial screening call with a recruiter to discuss the candidate's background and fit for the role
- Depth in Algorithms
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.
Technical Interviews
reportedOne or more technical interviews conducted via video call to assess technical skills.
What to demonstrate
- One or more technical interviews conducted via video call to assess technical skills
- Depth in Algorithms
How to prepare
- Answer aloud and timed: What is a RESTful API, and how does it differ from SOAP?
- Answer aloud and timed: Describe the concept of microservices and its advantages.
Onsite Interview
reportedMultiple rounds of interviews onsite, including a presentation of a take-home project and coding exercises.
What to demonstrate
- Multiple rounds of interviews onsite
- Including a presentation of a take-home project and coding exercises
How to prepare
- Answer aloud and timed: How do you manage version control in your projects?
- Answer aloud and timed: Write a function to find the maximum subarray sum.
Team Discussions
reportedDiscussions with various team members to evaluate cultural fit and collaboration skills.
What to demonstrate
- Discussions with various team members to evaluate cultural fit and collaboration skills
- Depth in Algorithms
How to prepare
- Answer aloud and timed: Given a binary tree, implement a function to perform an in-order traversal.
- Answer aloud and timed: How would you implement a hash map from scratch?
1 candidate reports. Individual accounts describe a particular role and hiring cycle.
Zest AI Data Scientist Interview Experience — Eight Rounds, Then Ghosted by a Vanishing HR
Let me share the funniest interview experience I've had recently. I saw the posting online and applied on a whim. The recruiter emailed me to reach out. From start to finish there were 8 rounds total. Yes, 8, for a company this small. First was the hiring manager round: resume and machine learning concepts. Then a technical screen. The first question showed a graph where training, testing, and va…
Read full experiencePracHub editorial advice for the preparation topics above.
Going into the loop without having done this.
Practice coding under time constraints: Familiarize yourself with coding challenges that you may encounter during technical interviews by practicing on platforms like LeetCode or HackerRank.
Going into the loop without having done this.
Engage with the company’s mission: Understand Zest AI’s mission and values, as articulating how you can contribute to these will strengthen your candidacy.
Going into the loop without having done this.
Prepare for behavioral questions: Reflect on your past experiences and be ready to discuss them in a way that highlights your strengths and learning opportunities.
Going into the loop without having done this.
Leverage your network: If possible, reach out to current or former employees to gain insights into the interview process and company culture.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to find the maximum subarray sum.
Write a function to find the maximum subarray sum.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Given a binary tree, implement a function to perform an in-order traversal.
Given a binary tree, implement a function to perform an in-order traversal.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
How would you implement a hash map from scratch?
How would you implement a hash map from scratch?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Solve a problem using dynamic programming—give an example.
Solve a problem using dynamic programming—give an example.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
Explain the time complexity of your solution for the previous question.
Explain the time complexity of your solution for the previous question.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- 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?
How would you optimize a database query for performance?
How would you optimize a database query for performance?
Approach
- Name the grain you start from and join outward from it.
- Check whether any join is one-to-many before aggregating, or the sums inflate.
- Say which index the query would use, and what makes it unusable.
- Handle the rows that do not match: that is usually the actual question.
Follow-up
- How does the query change if that join becomes one-to-many?
- What happens to this when the table is ten times larger?
Explain why the owner filter ignores the listing index
The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.
Approach
- Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
- For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
- Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
- Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.
Follow-up
- 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
- A dashboard runs this for 40 owners in one page load. What changes about the design?
Explain the difference between a stack and a queue.
Explain the difference between a stack and a queue.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What is a RESTful API, and how does it differ from SOAP?
What is a RESTful API, and how does it differ from SOAP?
Approach
- Say who the caller is and what they do when the call fails halfway.
- Define the identity of a request so a retry cannot double-apply it.
- Separate accepted, pending, failed and confirmed; they are different facts.
- Design the error taxonomy before the success shape; callers branch on it.
Follow-up
- What happens if the caller retries after a timeout?
- How does a client discover it is on an old version of this contract?
Describe the concept of microservices and its advantages.
Describe the concept of microservices and its advantages.
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
How do you manage version control in your projects?
How do you manage version control in your projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
A client is experiencing slow performance with their current system. How would you approach diagnosing the iss
A client is experiencing slow performance with their current system. How would you approach diagnosing the issue?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
You need to design a system for a new feature. Walk me through your thought process.
You need to design a system for a new feature. Walk me through your thought process.
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Given a scenario where user data is compromised, what steps would you take to mitigate the situation?
Given a scenario where user data is compromised, what steps would you take to mitigate the situation?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you approach scaling an application that has seen a sudden increase in users?
How would you approach scaling an application that has seen a sudden increase in users?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Discuss a time you had to pivot your approach based on new information.
Discuss a time you had to pivot your approach based on new information.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
One customer endpoint stalls deliveries to every other destination
The egress service delivers about 1.5k webhooks/second across 40,000 destinations, with a per-destination concurrency cap of 4 and a 10-second connect-plus-read timeout. Throughput falls to 300/second, queue depth climbs, and p99 delivery latency for unaffected destinations goes from 200 ms to minutes, while the error rate barely moves. One tenant holds 900 destination rows whose URLs share a hostname that now answers in 9.5 seconds. Explain the mechanism with the arithmetic, then give the containment in the order you would apply it.
Approach
- Look at saturation before errors. A flat error rate with collapsing throughput says nothing is failing, things are waiting, so the first signal to pull is in-flight request count or pool wait time rather than the error counter. This is the distinction that decides the whole investigation.
- Group in-flight work by resolved host, not by destination id. The cap is keyed per destination row, so 900 rows sharing one hostname buy 3,600 concurrent slots against a single host, each held for 9.5 seconds. The bulkhead was never a bulkhead for that host, and grouping by the wrong dimension is why the dashboard looked healthy.
- Do the arithmetic in both directions. Required concurrency is arrival rate times latency, so 1.5k/second at 200 ms needs about 300 in flight, which is entirely consumed by 3,600 slow slots; conversely whatever concurrency is left sustains rate equals concurrency divided by 9.5 seconds, which is the 300/second you are seeing. Matching both numbers is what promotes this from a plausible story to the mechanism.
- Explain why the circuit breaker never helped. It opens on consecutive failures, and a 9.5-second response inside a 10-second timeout is a success. Slow is not failing, so an error-rate breaker cannot see this; you need a slow-call ratio, a deadline propagated from the caller's remaining budget, or a concurrency limiter.
Follow-up
- The host recovers to 80 ms. How long does the queue take to drain, and what does the drain do to the recovered host?
- Where should the 10-second timeout number actually come from?
Built from the rounds and topics Zest AI candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Zest AI loop
- Write out the reported sequence: Phone Screen, Technical Interviews, Onsite Interview, Team Discussions.
- 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 4 reported rounds, with the weakest marked.
02Work Algorithms
- Spend the session on Algorithms, which Zest AI candidates report being tested on.
- Write one worked example in Algorithms and time yourself on it.
Deliverable: One timed worked example in Algorithms.
03Work Whiteboard Programming
- Spend the session on Whiteboard Programming, which Zest AI candidates report being tested on.
- Write one worked example in Whiteboard Programming and time yourself on it.
Deliverable: One timed worked example in Whiteboard Programming.
04Work Problem Solving
- Spend the session on Problem Solving, which Zest AI candidates report being tested on.
- Write one worked example in Problem Solving and time yourself on it.
Deliverable: One timed worked example in Problem Solving.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: Explain the difference between a stack and a queue.
- Answer aloud, timed: How would you optimize a database query for performance?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Coding / Algorithms
- Answer aloud, timed: Write a function to find the maximum subarray sum.
- Answer aloud, timed: Given a binary tree, implement a function to perform an in-order traversal.
Deliverable: Spoken answers to 2 reported Coding / Algorithms question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a challenging project you worked on. What was your role, and what did you learn?
- Answer aloud, timed: How do you handle disagreements with team members?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Describe a challenging project you worked on. What was your role, and what did you learn?
Describe a challenging project you worked on. What was your role, and what did you learn?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
How do you handle disagreements with team members?
How do you handle disagreements with team members?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
Can you provide an example of when you took the lead on a project?
Can you provide an example of when you took the lead on a project?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
What motivates you to perform well in your job?
What motivates you to perform well in your job?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
How do you prioritize your tasks when managing multiple projects?
How do you prioritize your tasks when managing multiple projects?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- 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?
- 01
Describe a challenging project you worked on. What was your role, and what did you learn?
- 02
How do you handle disagreements with team members?
- 03
Can you provide an example of when you took the lead on a project?
- 04
What motivates you to perform well in your job?
What is the typical interview difficulty level for a Software Engineer at Zest AI?
The interview process can be challenging, especially for technical interviews that require strong problem-solving and coding skills. Candidates should anticipate a mix of behavioral and technical questions.
Zest AI Software Engineer candidate reports ↗How long does the interview process usually take?
The timeline from initial contact to offer can vary, but candidates typically complete the process within a month, including multiple rounds of interviews.
Zest AI Software Engineer candidate reports ↗What differentiates successful candidates at Zest AI?
Successful candidates demonstrate strong technical expertise, effective communication skills, and a collaborative mindset. They align well with the company's values and show a passion for innovation in fintech.
Zest AI Software Engineer candidate reports ↗What is the company culture like at Zest AI?
The culture at Zest AI emphasizes teamwork, transparency, and a commitment to solving real-world problems through technology. Employees often cite a supportive environment that encourages growth and learning.
Zest AI Software Engineer candidate reports ↗Are there opportunities for remote work or flexible schedules?
Zest AI has embraced flexible working arrangements, and many employees enjoy the option of remote work or hybrid schedules depending on their roles and team dynamics.
Zest AI Software Engineer candidate reports ↗How hard is the Zest AI interview?
Candidates most commonly rate Zest AI interviews as medium, based on 83 reported interviews. About 14% of candidates who interview go on to receive an offer.
Zest AI Software Engineer candidate reports ↗What topics does Zest AI test in interviews?
Zest AI interviews most often cover Data Analysis, Exploratory Data Analysis (EDA), Presentation Skills, Statistics, and Problem Solving. The exact emphasis depends on the specific role you apply for.
Zest AI Software Engineer candidate reports ↗Is Zest AI a good place to work?
Employees rate Zest AI 4.0 out of 5 overall, based on aggregated workplace reviews spanning career growth, work-life balance, compensation, culture, and management.
Zest AI Software Engineer candidate reports ↗Where is Zest AI headquartered?
Zest AI is headquartered in Burbank, CA.
Zest AI Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
Official role evidence, timestamped platform data and clearly labeled preparation advice.
- 01Zest AI Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
candidate · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
platform · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
platform · Accessed 2026-09-22
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