xAI Interview Questions — Page 3

xAI·Software Engineer·Technical Phone Screen

Apr 2026

xAI software engineer interview, got a meaty in-memory database design problem that was more involved than I expected for a single coding round. The nested transaction piece especially caught me flat-footed at first.

Design and implement an in-memory key-value store that supports versioned, nested transactions with begin, commit, and rollback operations. Gets should traverse from the innermost transaction outward, and commits should merge changes into the parent scope rather than directly to the store.

“I got the basic set/get/delete part pretty quickly.”

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xAI·Machine Learning Engineer·Onsite - Cross-functional / Panel

May 2026

xAI ML Engineer loop included a 'meet the team' presentation where you had to prep a full solo talk covering your best project, your motivation for joining, and your goals. Multiple team members were in the room and could fire follow-ups at any point. Not a typical panel.

Walk us through your most impressive project: what was the problem, how did you approach it, what was the impact, and what did you learn from it?
Why do you want to join this company and this team specifically?
What kind of problems do you want to work on here, and what impact are you hoping to have?

“This is the centerpiece of the whole session so you can't wing it.”

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

May 2026

System design question for an ML Engineer role at xAI. The whole thing revolved around one meaty data structure problem with a bunch of follow-ups layered on top. Pretty intense for what felt like a single question.

Design a data structure that supports insert, remove, and get_random operations, all in expected O(1) time. Walk through your algorithm choices, how you handle edge cases like deleting the last element or filling gaps, how you'd verify the randomness is actually uniform, and how you'd extend it to support duplicates or thread-safety.

“The core idea clicked pretty fast for me: combine a hashmap with a dynamic array.”

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xAI·Machine Learning Engineer·Onsite - Multi Round

May 2026

Interviewed for an ML Engineer role at xAI. Each loop round starts with a project walkthrough before moving into a short coding or system design segment. Pretty structured format once you know what to expect.

Walk me through a recent project you worked on: your role, the technical approach, the outcome, and what you took away from it.

“This opens every round, so you'd think I'd have been more prepared.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

xAI SWE interview, got a data processing problem involving event logs for Twitter Spaces. The main question was meaty enough but the follow-up is what actually made me sweat.

Given a log of events (create, join, leave) for Twitter Spaces with timestamps and user IDs, compute the total active user-hours for each space.
Follow-up: given a continuous stream of these events in real time, how would you return the top-K spaces by current active user count at any moment?

“The core idea clicked pretty fast: track when each user enters a space and subtract when they leave.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

Got a coding question from xAI that was basically the combination sum variant where each element can only be used once. Pretty standard backtracking problem but the duplicate handling trips people up if you haven't seen it.

Given a list of candidate numbers and a target, find all unique combinations that sum to the target, where each number can only be used once.

“The 'no duplicates in the result' constraint is where people slip up.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

xAI SWE interview that went deep on a streaming data problem. The question started familiar then got complicated fast once memory constraints entered the picture.

You have a stream of incoming data. For any sliding window defined by either the last T seconds or the last N events, return the kth largest value. Memory is limited so you can't store everything. Walk through your approach including how you'd manage the window, handle bucketing, and analyze the time complexity for updates and queries.

“Started okay because I recognized the kth-largest pattern from the classic heap version.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

Quick 15-minute screen for a Software Engineer role at xAI, candidate-led format where you introduce yourself and then walk through a recent technical challenge. The follow-ups come fast and they drill into specifics, so vague answers won't survive long.

Walk me through your background and what you've been working on recently.
Describe a recent technical challenge: what was the project, what specifically did you own, what was the hardest part, and how did you tackle it?

“Felt fine until I realized I was burning half the screen time on this.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

xAI interview, looked like an ML infra or systems engineering role based on the question. One meaty coding/design problem about building a batched decoding loop for a language model. Pretty niche but makes sense given what they're building.

You're given a simulated LLM interface where each call takes a batch of token-prefix sequences and returns the next token per sequence. Implement a dynamic batching loop: maintain a fixed number of active slots and a waiting queue, fill empty slots as sequences finish, route results correctly via a slot-to-sequence mapping, and handle stop conditions and per-sequence callbacks. Also discuss correctness edge cases around sequences finishing at different times versus naive whole-batch decoding.

“This one took me a minute to even parse.”

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xAI·Software Engineer·Technical Phone Screen

May 2026

xAI software engineer interview, got a rate limiter design problem that started simple and then expanded into distributed systems territory pretty fast. solid problem but the discussion portion is where it got interesting.

Implement a token bucket rate limiter with a configurable capacity and refill rate, where allow(timestamp, n) checks if n tokens are available and deducts them if so. How would you handle concurrent access?
How would you extend this to a distributed token bucket shared across multiple service instances, for example using Redis? What are the consistency and performance tradeoffs?
How would you design this to support per-user rate limits versus a single global limit, and what fairness considerations come up?

“I started with the single-threaded version pretty quickly, bucket capacity, refill math based on elapsed time, the usual.”

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