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Roblox interview notes, page 11 of 15

Large Enterprises

Most of these Roblox write-ups come from Software Engineers (79), then Data Scientists (38) and Machine Learning Engineers (17). The most reported rounds are the technical phone screen (85), the system design round (39), the online assessment (6) and the behavioral / leadership round (3).

142 interview notes · updated Sep 2026

Roblox·Machine Learning Engineer·Technical Phone Screen

Jun 2026
Coding screen for an MLE role at Roblox, pretty standard stuff centered around log processing. The question was straightforward but the follow-up directions they hinted at made it clear they wanted to see if you could think beyond the naive solution.
  • Given a sequence of application log entries (each being a function or API call name), write a function that returns the most frequently occurring call along with its count. Be prepared to discuss handling ties, returning the top-k most frequent calls, and scaling to streaming or large-scale log data.

“Nailed the basic part fast, just a hashmap frequency count and a linear scan for the max.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jun 2026
Roblox system design round focused on an audio detection system, and the metrics/evaluation portion was way more involved than I expected. Less about architecture and more about how you'd actually know if the thing was working.
  • How would you define and monitor success for an audio detection system, covering both product metrics like precision/recall and per-class error rates, and system metrics like latency, throughput, and cost per hour of audio?
  • Walk me through how you'd set alert thresholds and design dashboards for this kind of ML-powered system, and what signals would actually tell you something is going wrong before users notice.
  • How would you safely roll out a new model or updated detection threshold, including shadow evaluations and A/B testing strategies before full deployment?

“This sprawled fast.”

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Roblox·Software Engineer·Technical Phone Screen

Jun 2026
Roblox technical phone screen for a software engineer role, basically one meaty graph problem that spiraled into a full complexity analysis discussion. Felt pretty solid on the core algorithm but the tie-breaking extension and the DFS contrast tripped me up a bit.
  • Given a DAG of N tasks with directed prerequisite edges, return a valid execution order. When multiple tasks are ready to run at the same time, break ties using a provided ordering criterion (like ascending task ID, descending priority, or a custom comparator). Also detect and report cycles if no valid order exists.

“I jumped straight to Kahn's algorithm which was the right call, but I fumbled the tie-breaking part for a bit.”

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Roblox·Software Engineer·Technical Phone Screen

Jun 2026
Did a technical screen for a Software Engineer role at Roblox. Just one coding problem, grid traversal stuff, pretty standard but I fumbled around a bit before getting to a clean solution.
  • Given a 2D grid with a start cell, a target cell, obstacle cells, and free cells, determine whether there is a valid path from start to target moving in four directions without stepping on obstacles or leaving the grid.

“Classic reachability problem.”

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Roblox·Software Engineer·Technical Phone Screen

Jun 2026
Roblox software engineering interview with a parsing and data structure problem. Pretty focused on getting the implementation right under pressure.
  • Given a log of function call and return events, parse the log to reconstruct the active call path at every point in time, then count how many times each distinct call path appears across the entire log and return a mapping of call path to count.

“The stack part clicked fast but I fumbled a bit on how to serialize the path for the hash map key.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jun 2026
System design round at Roblox where you basically drive the whole thing yourself. The interviewer stays quiet while you talk through a To-Do app design, then pivots hard into storage and conflict resolution specifics. More depth required than I expected for what sounds like a simple product.
  • Design a To-Do list application. You drive the requirements and architecture. The interviewer will follow up on schema and storage decisions.
  • How would you handle concurrent edits to the same task by two collaborators on a shared list?
  • Walk me through how offline clients should sync when they come back online after making local changes.

“The open-ended format tripped me up at first.”

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Roblox·Machine Learning Engineer·Technical Phone Screen

Jun 2026
Roblox ML Engineer interview with a sliding window coding problem. Pretty focused session, just the one algorithmic question from what I can tell, and the constraint to hit O(n) was the whole point of the exercise.
  • Given a list of integers, a target value, and a fixed window size k, find all contiguous windows of size k that contain at least one occurrence of the target. Return the start and end indices of each such window. You need to do this in O(n) time using a counter to track how many times the target appears in the current window.

“The O(n) constraint is where this gets interesting.”

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Roblox·Software Engineer·Technical Phone Screen

Jun 2026
Roblox SWE interview that went deep on rate limiting, starting simple and then layering in multi-dimensional constraints. The design got surprisingly tricky once they added the dual-counter requirement.
  • Implement a rate limiter with an allow(timestamp) method that returns true if the request falls within K requests per rolling window of W milliseconds, assuming timestamps are nondecreasing.
  • Extend the rate limiter to allow(userId, experience, timestamp) that enforces independent per-user and per-experience limits, succeeding only if both are satisfied, and updates both counters atomically.
  • What are the time and space complexities of your rate limiter implementation, and how would you garbage-collect stale keys over time?

“The sliding window part is where I tripped up a bit.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jun 2026
System design round at Roblox focused entirely on building a payment processing system. It was a deep one, covered a lot of ground, and I left feeling like I'd done okay on the broad strokes but got a bit shaky on some of the distributed systems specifics.
  • Design a payment processing system that supports multiple payment methods (card, wallet, bank transfer), refunds, and reconciliation.
  • How would you handle idempotency in a payment system, especially when retrying requests to an external payment gateway?
  • Walk me through how you'd achieve exactly-once payment semantics in a distributed system using sagas or distributed transactions.
  • How would you design the system to meet PCI compliance and security requirements for handling card data?
  • How would you design the fraud detection component and integrate it into the payment flow?
  • What monitoring and observability would you put in place for a payment system, and what metrics matter most?

“I started with the API surface and worked outward, which felt right.”

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Roblox·Data Scientist·Technical Phone Screen

Jun 2026
Roblox data scientist interview with a stats-heavy coding question around causal inference. The problem was well-defined but had enough edge cases to trip you up if you weren't thinking carefully about the data.
  • Given three parallel arrays representing period (pre/post), treatment group, and outcome values, implement a difference-in-differences estimator that computes the treatment effect across the four group-period cells.
  • Extend the DID implementation to flag potential pre-trend violations: compute the pre-period difference between treated and control groups and return a boolean indicating whether it exceeds a given threshold.

“The formula itself isn't hard once you see it written out.”

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