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Reddit·Machine Learning Engineer·Onsite - Behavioral / Leadership·Senior

Senior
Jul 2026

Summary

Behavioral round for an ML Engineer role at Reddit. Two questions, both the classic failure/success combo. Nothing surprising about the format but the bar for specificity felt higher than I expected.

Questions Asked (2)

Q1

Describe a time something didn't go as planned in your work. What happened, what did you take away from it, and what would you change if you could do it over?

Adaptability & AmbiguityRoot Cause Analysis
Author's notes

I went with an incident from a model rollout that caused some downstream noise in a recommendation pipeline.

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AI HintsAI Generated

Suggested Approach

Choose a specific ML project failure where you can clearly articulate the root cause and your learning. Use a structured narrative like STAR to describe the situation, your actions, and the outcome, then reflect on what you'd do differently. Emphasize how you turned the failure into a process improvement or better decision-making in future projects.

Pro tip: Show self-awareness by acknowledging your own contribution to the failure without being overly self-critical, and highlight how you implemented a systemic fix to prevent similar issues. This demonstrates maturity and a growth mindset.

1. Set the Context

Briefly describe the project, your role, and the goal. Keep it concise to focus on the failure and learnings.

2. Describe the Failure

Explain what didn't go as planned, including the specific impact (e.g., model performance drop, missed deadline). Be honest but not overly negative.

3. Analyze Root Cause

Detail how you investigated the issue to find the underlying cause. Mention tools or methods (e.g., debugging, data validation, A/B test analysis).

4. Share Key Takeaways

Articulate the lessons learned, such as the importance of robust validation, communication, or iterative testing.

5. Propose Improvements

Explain what you would change if you could do it over, and how you've applied these changes to subsequent projects.

Key Points to Mention

  • Specific ML technical details (e.g., data drift, overfitting, pipeline bug) to show expertise
  • Root cause analysis process (e.g., using logs, metrics, or experiments)
  • Quantifiable impact of the failure (e.g., 10% drop in accuracy, delayed launch)
  • Lessons learned and how they changed your approach
  • Systemic improvements implemented (e.g., new monitoring, validation steps)
  • Alignment with Reddit's values (e.g., user impact, scalability, experimentation)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

Walk me through a time you succeeded at something. What specifically did you contribute and what was the measurable impact?

Cross-functional AlignmentStakeholder Management
Author's notes

This one tripped me up a little because I defaulted to a team win and had to backpedal when they pushed on my individual contribution.

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AI HintsAI Generated

Suggested Approach

Choose a project where you drove a measurable ML outcome, ideally one that required cross-functional collaboration. Structure your answer using a clear framework like STAR, emphasizing your specific technical contributions and the quantifiable business impact. Highlight how you aligned stakeholders and navigated trade-offs to achieve success.

Pro tip: Quantify impact in terms of business metrics (e.g., revenue, engagement, retention) and connect your ML work directly to those outcomes. Also, briefly mention a key trade-off or challenge you navigated, showing maturity and stakeholder awareness.

1. Set the Context

Briefly describe the project, the business problem, and why it mattered to Reddit. Mention the cross-functional teams involved and your role.

2. Define the Goal and Metrics

State the specific, measurable objective (e.g., increase user engagement by X%) and how you aligned stakeholders on these metrics.

3. Describe Your Contribution

Detail the technical work you personally did: model design, experimentation, deployment, etc. Emphasize unique challenges and how you solved them.

4. Highlight Collaboration and Alignment

Explain how you worked with product, engineering, or other teams to integrate the solution and overcome obstacles. Show how you managed stakeholder expectations.

5. Quantify the Impact

Present the measurable results: improvements in key metrics, ROI, or efficiency gains. Tie back to business outcomes and learnings.

Key Points to Mention

  • Specific ML techniques or models you implemented and why they were chosen
  • Cross-functional collaboration: how you aligned with product, engineering, and data teams
  • Stakeholder management: how you communicated progress, risks, and trade-offs
  • Measurable impact: quantitative results (e.g., 15% increase in click-through rate, 10% lift in retention)
  • Challenges faced and how you navigated them (e.g., data quality, latency constraints)
  • Business relevance: how the success tied to Reddit's goals (e.g., user growth, engagement)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.