Backpropagation

Tech Deep DiveOpenAILast reported September 2026High Frequency
Reported
13× across candidate reports
First seen
February 2025
Last reported
September 2026
Reported outcome
mixed

Problem Overview

OpenAI technical deep-dive question, reconstructed from 13 candidate reports (February 2025 to September 2026). Candidates reported 4 follow-ups.

  • 4 candidate-reported follow-ups — the probes candidates report being asked, with the trigger for each
  • The full problem statement — full requirements, constraints, and edge cases
  • Approach and trade-offs — what passing candidates did, and the mistakes that sink people
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Verified Source
Every question is reconstructed from multiple independent candidate reports. Follow-ups candidates reported, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The follow-ups candidates reported, with the trigger that prompts each one — plus the mistakes that sink people.
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