← Back to Directory

OpenAI interview notes, page 16 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·Software Engineer·Onsite - Behavioral / Leadership

Apr 2026
Behavioral screen for a software engineer role at OpenAI. Pretty standard format: interviewer led with a company-specific question, ran through a few more behavioral prompts, then flipped it over to me for questions at the end.
  • Why do you want to work at OpenAI?

“I'd put real work into this one beforehand, not just a generic 'I love AI' answer.”

View Post

OpenAI·Machine Learning Engineer·Onsite - Coding / Algorithms

Apr 2026
Round 3 of the OpenAI MLE loop was a one-hour ML coding session focused on implementing matrix multiplication from scratch in PyTorch, including the backward pass. The main question was recognizable from prep forums but the follow-up involving a parallel scan algorithm was a genuine surprise.
  • Implement the forward pass and backpropagation for matrix multiplication in PyTorch, given a code skeleton.
  • Extend your backpropagation implementation using a parallel prefix scan approach (similar to the Hillis-Steele algorithm).

“Had seen this one floating around online so the forward pass felt manageable.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
Got a system design coding question for a software engineer role at OpenAI. The problem was a versioned social follow graph with friend recommendations, basically build the whole thing in memory from scratch. Pretty involved for a single session.
  • Design and implement an in-memory versioned social follow graph that supports follow/unfollow mutations with timestamps, point-in-time relationship queries, and a scored friend recommendation system based on mutual followees.

“This one has a lot of moving parts.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at OpenAI for a software engineer role, focused entirely on designing a cloud-based IDE from scratch. Dense question with a lot of surface area, felt like I was triaging the whole time rather than going deep on anything.
  • Design a cloud-based IDE similar to Codespaces or Replit. Walk through containerized workspace provisioning per user, file system persistence, real-time editor sync, terminal and language server multiplexing, sandboxed build and run environments, collaborative editing, and how you'd handle cost and idle workspaces at scale.

“This question is basically five system design questions stapled together.”

View Post

OpenAI·Software Engineer·Technical Phone Screen

Apr 2026
Distributed systems deep dive at OpenAI for a software engineering role. The whole interview was one long thread pulling on a single network topology problem, going from basic message passing all the way through fault tolerance. Felt like a gauntlet.
  • In a network where each node only knows its parent and children and can only send messages to those neighbors, how would you implement a reliable message delivery interface between adjacent nodes?
  • Using only message passing in this network, design an algorithm to count the total number of nodes. State your assumptions about the topology and analyze the message and time complexity.
  • Design a protocol to find the path from any node to the root, and then extend it to find the path between two arbitrary nodes in the network.
  • The network can experience message loss, duplication, reordering, and node crashes. How would you handle these failures using timeouts, retries, acknowledgments, and idempotent operations? Address correctness and complexity.

“Started with a simple send-and-ack approach.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
Did a system design round at OpenAI for a software engineer role. The whole thing was one deep problem about binary serialization for a key-value store, which sounds narrow but ended up covering a lot of ground fast.
  • Design and implement a binary serialization format for an in-memory key-value store. Keys are UTF-8 strings, values can be int64, float64, bool, string, or nested maps. Your format needs a magic header, version field, type tags, length prefixes, endianness convention, and checksums. Implement encode and decode in O(n) time. Then discuss the tradeoffs versus JSON or MessagePack.

“This was the whole interview, basically.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at OpenAI for a software engineer role. The main problem was building an in-memory key-value store with persistence, which sounds straightforward until you get into the weeds on serialization and crash consistency.
  • Design and implement an in-memory key-value store with a persistence layer. You need four operations: set, get, shutdown, and restore. On shutdown the store flushes to bytes; on restore it rebuilds from those bytes. Walk through the medium interface, serialization format, error handling, crash consistency, performance, and how you'd test it.

“This question has a lot of surface area and I think I underestimated how deep they wanted to go on each sub-part.”

View Post

OpenAI·Data Scientist·Technical Phone Screen

Apr 2026
Interviewed for a Data Scientist role at OpenAI and the technical portion was heavily focused on subscription event pipelines, schema design, and some code review work. Felt like a solid systems-thinking test more than a pure SQL grind.
  • Design a raw event table schema that can support deriving a user's current subscription status as well as their full historical state over time.
  • Write SQL or Python logic that produces one row per user showing their latest subscription status, correctly handling the case where a user has signed up, cancelled, and signed up again.
  • Review a Python snippet that assigns experiment variants and delivers a free-trial offer. Identify at least three improvements or safeguards you would add.

“This felt like a warmup but it actually took me a second to think through.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at OpenAI for a software engineer role, focused entirely on building a cloud-based coding environment from scratch. One long question that kept branching into harder sub-problems every time I thought I'd covered enough ground.
  • Design a virtual in-browser coding environment similar to GitHub Codespaces or Replit, where users get a remote workspace with an editor, terminal, and sandboxed runtime.

“I started with container provisioning per user which felt like the obvious entry point, but the interviewer kept pulling the thread on things I glossed over.”

View Post

OpenAI·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at OpenAI for a software engineer role, focused entirely on designing a payment system from scratch. The question was dense and they clearly expected you to cover a lot of ground without much prompting.
  • Design a payment system that supports placing holds on funds, batch processing of those holds (capture, release, or expiry), and direct charges. Cover the data model, idempotency, two-phase commit semantics, retry and timeout behavior, refunds, fraud detection, double-spend prevention, ledger design, reconciliation, observability, and how you'd scale it.

“This thing has so many layers that I spent the first few minutes just trying to figure out where to start.”

View Post