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OpenAI interview notes, page 23 of 67

Mid-sized

Most of these OpenAI write-ups come from Software Engineers (460), then Machine Learning Engineers (137) and Backend Engineers (23). The most reported rounds are the technical phone screen (335), the system design round (229), the onsite coding round (32) and the behavioral / leadership round (22).

667 interview notes · updated Jul 2026

OpenAI·Machine Learning Engineer·Technical Phone Screen

May 2026
Interviewed for an ML Engineer role at OpenAI and got hit with a pretty deep question about numerical stability in mixed-precision training. Not a lot of hand-holding in the format, just one meaty technical problem to work through.
  • How would you handle numerical overflow when training with FP8 and BF16 in a mixed-precision setup?

“This tripped me up more than I expected.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at OpenAI for a software engineer role. One question, 60 minutes, entirely focused on designing a payment service with a very specific constraint around double-charging. The depth they expected was pretty serious.
  • Design a payment service that sits between a point-of-sale machine and a downstream banking system, handling the full authorize-and-capture flow. The core constraint: a user must never be charged twice, even if the network drops mid-request or the POS retries the operation multiple times.

“This felt manageable at first and then quietly became a lot.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at OpenAI for a software engineer role. The interviewer was quiet and gave almost nothing away, which made it hard to read how things were going. Came out feeling pretty good about it.
  • Design a chess game.
  • How would you handle each player's move timer, given that you can't trust the client to report time accurately?

“Prepped this one from a video walkthrough and it paid off.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at OpenAI for a software engineering role. The prompt was to design a Slack-like messaging product end to end, covering everything from real-time delivery to search and notifications. Pretty broad scope for a single session.
  • Design a Slack-like team collaboration product with support for workspaces, channels, direct messages, real-time delivery, message history, search, and notifications.
  • Walk through your data model for messages, channels, and workspaces, and explain how you'd shard the storage layer.
  • How would you implement message search within a workspace?
  • Describe how notifications would work across mentions, direct messages, and channel activity, including delivery to mobile and web.
  • What are the major bottlenecks and trade-offs in your design, particularly around high availability and consistency for message ordering?

“This is basically a full system design in one question.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026
Interviewed for a software engineering role at OpenAI and got a system design question to design ChatGPT itself. Kind of surreal being asked to design the product you're interviewing to work on.
  • Design ChatGPT. Walk through the architecture of a large-scale conversational AI product from scratch.

“This one is deceptively massive.”

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OpenAI·Software Engineer·Onsite - Behavioral / Leadership

May 2026
Behavioral screen for a SWE role at OpenAI. Just the one question from what I can tell, pretty standard stuff but OpenAI tends to push harder on the follow-ups than most places.
  • Tell me about a time something went seriously wrong on a project and how you handled it.

“Classic question but I always fumble the 'how you reacted' part because I focus too much on explaining the situation.”

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OpenAI·Software Engineer·Onsite - Behavioral / Leadership

May 2026
Past project round at OpenAI for a software engineer role. They dig into your projects pretty granularly, not just the high-level pitch.
  • Why did you choose to work on this particular project?
  • How many people were on your team for this project?

“They wanted more than just 'it was assigned to me.' Had to actually explain the reasoning behind picking it, which I wasn't fully prepared for.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at OpenAI, one big question about building a payment platform from scratch. The scope was massive and I'm not sure I handled the scale requirements well enough.
  • Design a payment processing system for a global platform that supports user-to-user payments, refunds, and transaction history, with high availability, security, and the ability to handle 10,000 transactions per second at peak.

“I started with the data model and probably spent too long there.”

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OpenAI·Machine Learning Engineer·Technical Phone Screen

May 2026
Interviewed for an ML Engineer role at OpenAI and got hit with a pretty theoretical question about nearest neighbor search. Short round, one meaty question, left me second-guessing my answer the whole way home.
  • If you switched from L2 to L1 distance, how would you implement 1-nearest-neighbor classification using a neural network?

“I fumbled around for a bit trying to remember how L1 differs from L2 in terms of gradients and what that means for a network you'd actually train.”

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OpenAI·Software Engineer·Technical Phone Screen

May 2026
Technical screen for a software engineer role at OpenAI covering JavaScript runtime fundamentals and React hooks. Pretty conceptual, no leetcode, which was a nice change. Felt like they wanted to see how well you could explain things, not just whether you knew the answer.
  • How does JavaScript's execution model work, is it single-threaded, and how does it handle concurrency?
  • What's the difference between useState and useRef in React, and when would you actually use one over the other?

“I knew the event loop stuff but fumbled a bit explaining why JS is single-threaded by design versus just a limitation.”

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