OpenAI interview notes, page 31 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

ML coding round at OpenAI for a machine learning engineer role. They had me build a classifier from scratch, which sounds manageable until you're live-coding a training loop and someone's watching every keystroke.

Implement a classifier from scratch (logistic regression or a small neural network), including the loss function, gradient updates, training loop, and model evaluation.

“I went with logistic regression because I figured it'd be cleaner to reason about under pressure.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at OpenAI for a software engineer role, two interviewers, focused on a payment processing system. The question had a lot of surface area and I ran out of time on the part that mattered most.

Design a payment system that handles purchase requests, approval states, and batch settlement at midnight by generating a large file of all transactions from the day.

“Spent way too long on the API and DB layers and basically ran out of runway before getting to the file generation piece, which was clearly the whole point.”

View Post

OpenAI·Machine Learning Engineer·Onsite - System Design / Architecture

May 2026

Deep-dive round at OpenAI for an MLE role, focused almost entirely on a past search system I'd built. They really wanted to get into the weeds on embedding design choices, not just hear a high-level story.

You used a hash-based representation for item IDs in your search system. Why not use BERT or another pretrained language model instead? Walk through the trade-offs.
When is a hash-based embedding approach appropriate versus a learned semantic embedding? What factors drive that decision?

“This is where the conversation got real.”

View Post

OpenAI·Machine Learning Engineer·Onsite - System Design / Architecture

May 2026

OpenAI ML Engineer interview with a system design question focused on building a real-time data cleaning pipeline at massive scale. Pretty intense scope for a single question, left feeling like I only scratched the surface.

How would you design a real-time data cleaning pipeline capable of handling massive-scale data?

“Spent the first few minutes just trying to scope it properly because 'massive scale' could mean a lot of things.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026

Two heavy system design prompts back to back for a software engineer role at OpenAI. The cloud IDE one went deeper than I expected into sandbox internals, and the payment system prompt was basically a distributed systems gauntlet. Felt like a senior-level bar the whole way through.

Design a cloud-based IDE where users can write and run code in a browser, with execution happening inside isolated sandboxes. Walk through the full workflow including how the sandbox is set up, how user code runs, and how results get back to the browser.
How would you handle resource limits and malicious code in the sandbox environment, specifically around CPU, memory, network, and timeouts?
How does the system scale to support many concurrent workspaces without degrading performance?
Design a backend payment processing platform that merchants can use to charge customers through external payment providers. Cover the full payment lifecycle including state management, idempotency, webhook handling, and failure recovery.
How do you handle webhooks coming in from payment providers, including retries, ordering, and idempotency on your end?
What security and compliance considerations does a payment system need, and how do you build observability into it?

“This one went sideways for me around the execution scheduling piece.”

View Post

OpenAI·Machine Learning Engineer·Technical Phone Screen

May 2026

Got a scheduling problem for an ML Engineer role at OpenAI that was more of a combinatorics puzzle than anything ML-related. Took me a while to even understand what the constraints were asking before I could start coding.

Design a data labeling task scheduler that takes t tasks, m models, and h human labelers, and returns a schedule as a list of (task, model, human) tuples. The schedule must ensure each human participates in at least k tasks total, that at any prefix of the schedule the per-(task, model) and per-(task, human) assignment counts stay balanced (max minus min no greater than 1), and that no human labels the same task more than once.

“The constraint about prefixes is what got me.”

View Post

OpenAI·Mobile Engineer·Onsite - System Design / Architecture

May 2026

Interviewed for a Mobile Engineer role at OpenAI. Two rounds: system design first, then UI. The system design round was pretty thorough and covered a lot of ground. Came out of it feeling like I just barely held my own.

How would you design the API request layer for a mobile application? Walk through your approach, alternatives, and the tradeoffs involved.
Explain the ViewModel lifecycle across plain Java, Kotlin, and Kotlin with Compose. What are the key pitfalls and what can be optimized?
How do you approach concurrency in a mobile architecture? What patterns or mechanisms would you use and why?
How would you handle navigation architecture in a mobile app? What are the tradeoffs between different approaches?

“Went with HTTP, pretty standard choice.”

View Post

OpenAI·Backend Engineer·Hiring Manager Screen

May 2026

Interviewed for a backend role at OpenAI and got a career trajectory question that felt more like a therapy session than a technical screen. Not bad, just unexpected.

Walk me through your career so far. What key decisions and projects shaped where you are now, what drove each move, and what does that tell you about what you want next?

“I rambled.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at OpenAI for a software engineer role, focused entirely on designing an online chess platform from scratch. The question had a lot of moving parts and the depth they expected was pretty serious.

Design an online chess service that supports matchmaking and real-time gameplay. Cover queue design, Elo-based skill matching, game state management over WebSocket, server-side move validation, clocks, disconnects, and how you'd scale and shard game servers.

“This one sprawled fast.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at OpenAI for a software engineering role. The whole thing centered on designing something like Sora, with a lot of back-and-forth on scheduling, what happens when things break, and how you'd monitor the system in production.

Design a large-scale video generation system similar to Sora, covering job scheduling, failure handling, and observability.

“This is a meaty one and I don't think I fully appreciated how deep the failure scenarios would go.”

View Post