OpenAI Interview Questions — Page 52

OpenAI·Software Engineer·Technical Phone Screen

Jun 2026

Interviewed for a software engineer role at OpenAI and got a grid infection spread problem. Pretty standard BFS territory but the edge case around unreachable cells tripped me up a bit.

Given an m x n grid where cells are either healthy or infected, infection spreads to all 4-directional neighbors each day. How many days until no further spread is possible? Return -1 if any healthy cell can never be reached.

“Knew pretty quickly it was multi-source BFS, seeded from all infected cells at once.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at OpenAI for a full-stack role, and it was a lot more sprawling than I expected. The question was basically 'build ChatGPT' which sounds fun until you realize they want you to go deep on like five different dimensions at once. I held it together but there were definitely moments where I was just winging it.

Design a ChatGPT-like service end to end, covering quota tracking for free-tier users, API design, client-side behavior, streaming responses, and backend topology.
How would you handle free-tier message limits, including quota tracking, error responses when a user hits the limit, and prompting them to upgrade?
Walk through your API design for this service: request/response structure, error codes, rate limiting strategy, and handling retries with idempotency.
How should the client handle retries, different error types, and conversation history that gets too long to fit in the model's context window?
Compare streaming versus non-streaming response delivery for this system. How would you implement SSE-based streaming and provide a fallback for clients that don't support it?
Describe the backend topology for this system: what services exist, how do they interact, and what does the request path look like from gateway to model serving to storage?

“This was the whole interview basically.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at OpenAI for a software engineer role. The main problem was LRU cache, which sounds straightforward until they keep adding layers to it.

Design a data structure that supports get and put operations in O(1) average time, evicting the least-recently-used entry when the capacity is exceeded.
How would you make this LRU cache thread-safe? Walk through the trade-offs between a single mutex, lock-free approaches, and sharded locking.
Extend the LRU cache to support TTL-based expiration. How would you design and implement that?

“I knew this one cold so I jumped straight to hashmap plus doubly-linked list.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round for a software engineering role at OpenAI, focused entirely on designing a GPU credit allocation system for a multi-tenant compute platform. The scope was massive and I kept second-guessing whether I was going deep enough on any one area.

Design a GPU credit allocation system for a multi-tenant compute platform, covering real-time consumption tracking, credit APIs, budget enforcement, job scheduling integration, prepaid/postpaid billing, fair-share usage, and operational concerns like idempotency, consistency, and observability.

“The question basically ate the whole session.”

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OpenAI·Machine Learning Engineer·Technical Phone Screen

Jun 2026

Interviewed for an ML Engineer role at OpenAI and got a coding round that was way more language-theory-heavy than I expected. They had me build a working interpreter from scratch, which felt closer to a compilers course than anything ML-adjacent.

Implement an interpreter for a small toy programming language that supports variable assignment, basic arithmetic operations, and a print statement. Then be prepared to extend it with conditionals, loops, or function calls.

“This wrecked me a little.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at OpenAI for a software engineer role. The interviewer was pretty no-nonsense and kept pushing on failure handling. Nothing catastrophic but nothing to brag about either.

Design a system similar to Sora, OpenAI's video generation platform.

“The bulk of the interview was really about failure modes, not the happy path.”

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OpenAI·Software Engineer·Onsite - System Design / Architecture

Jun 2026

OpenAI full-stack interview that blended frontend and system design into one question about building an AI playground. The scope was bigger than I expected and the conversation went pretty deep on sharing semantics and cost control, which I hadn't really prepped for.

Design a document-style AI playground where users can insert prompts at any position in the document and see responses rendered inline directly below each prompt. Walk through the data model and component structure.
How would you handle streaming LLM responses in this inline editor, including partial rendering and allowing the user to cancel mid-stream?
A user wants to save a prompt for later reuse. Where do you persist it, and how does the data model account for per-user vs. per-workspace ownership?
Walk through the sharing model: how do you scope access (link-based, specific users, public), handle permissions, and support revocation?
When a user shares a prompt, what data actually gets included? How do you handle privacy concerns around responses that might contain sensitive context or PII?
How do you design rate limiting and cost control for LLM API calls in this system?

“This tripped me up more than I expected.”

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OpenAI·Software Engineer·Technical Phone Screen

Jun 2026

Technical phone screen for a Software Engineer role at OpenAI, focused entirely on a deep C++20 metaprogramming problem around callable type introspection. Pretty niche stuff, definitely not a question you can wing.

Design a C++20 compile-time utility that checks whether a callable type matches a given function signature, including both a SFINAE/traits-based implementation and a concepts/requires-based one. It should support free functions, lambdas, functors, member function pointers, and std::function, and handle edge cases like noexcept, cv/ref qualifiers, and implicit conversions.

“This was the whole interview, basically.”

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

Jun 2026

Round 4 of the OpenAI ML Engineer loop was a one-hour system design focused on unsupervised/semi-supervised ML, and it was the kind of open-ended problem where you can spiral fast if you're not careful about keeping the interviewer in the loop.

Design an ML system that mines interesting or novel images from a massive unlabeled dataset. Human labelers can be part of the pipeline, but the system shouldn't depend on them too heavily.

“The open-endedness is what gets you here.”

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OpenAI·Backend Engineer·Technical Phone Screen

Jun 2026

Interviewed for a backend role at OpenAI and the whole thing basically centered on one deep project walkthrough. They wanted you to own the conversation, not just answer questions, which I was not fully prepared for.

Walk us through one of your most representative projects in depth, covering the scope, your role, technical decisions, how it touched different components, and the trade-offs you made along the way. Be ready to defend your choices.

“This is the kind of question that sounds easy until you're actually in it and realize they want you to lead, not just respond.”

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