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Openai·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
May 2026

Summary

Did a system design round for a Research Scientist role at OpenAI focused entirely on ML experiment infrastructure. The problem was meaty and I felt like I was playing catch-up for most of it.

Questions Asked (3)

Q1

Design and implement a flexible configuration system for ML experiments that supports declarative experiment definitions and multiple parameter sweep strategies like grid search, random search, and sequential sweeps.

System DesignTechnical Trade-offsA/B Testing & Experimentation
Author's notes

I jumped straight into the sweep mechanics and forgot to anchor on the config schema first.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a layered architecture separating experiment definition, parameter space specification, and sweep execution. Discuss trade-offs between flexibility, simplicity, and scalability, and outline how to implement each sweep strategy with a common interface.

Pro tip: Emphasize reproducibility and versioning of configurations, and mention how you would integrate with existing ML tooling (e.g., Kubernetes, Ray Tune) to avoid reinventing the wheel.

1. Clarify Requirements

Ask about scale, supported parameter types, integration needs, and whether the system should be declarative (e.g., YAML) or programmatic. Confirm expectations for sweep strategies and result tracking.

2. Design Core Abstractions

Define a configuration schema (e.g., using Pydantic or JSON Schema) and a ParameterSpace abstraction that supports discrete, continuous, and conditional parameters. Create a SweepStrategy interface with methods like `generate_trials()`.

3. Implement Sweep Strategies

For grid search, enumerate the Cartesian product; for random search, sample from distributions; for sequential sweeps, implement a scheduler that adapts based on results (e.g., Bayesian optimization). Ensure all strategies conform to the same interface.

4. Address Execution and Scalability

Discuss how to parallelize trials (e.g., using Ray, Dask, or Kubernetes), handle failures, and store results. Consider early stopping and resource allocation.

5. Discuss Trade-offs and Extensibility

Compare declarative vs. imperative approaches, built-in vs. external sweep libraries, and simplicity vs. advanced features. Explain how to extend the system for new sweep algorithms or parameter types.

Key Points to Mention

  • Declarative configuration using YAML/JSON with schema validation for reproducibility.
  • Parameter space specification supporting discrete, continuous, and conditional parameters.
  • Common interface for sweep strategies to allow pluggable algorithms.
  • Integration with existing ML orchestration tools (e.g., Ray Tune, Optuna) to leverage scalability and advanced algorithms.
  • Result tracking and versioning for experiment reproducibility and analysis.
  • Trade-offs between flexibility, complexity, and performance in system design.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

How would you handle experiment versioning and reproducibility in this system? What needs to be tracked and how do you ensure a run can be exactly reproduced later?

System DesignData ModelingTechnical Trade-offs
Author's notes

This is where I actually felt okay.

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AI HintsAI Generated

Suggested Approach

Start by defining what constitutes an experiment and the components that affect reproducibility: code, data, environment, and configuration. Then describe a versioning system that captures all these components, and explain how you would enforce and verify reproducibility, including trade-offs between storage and speed.

Pro tip: Emphasize that reproducibility is not just about storing artifacts but also about capturing the exact execution context and dependencies, and mention the importance of immutable infrastructure and deterministic builds.

1. Identify Components

List all elements that influence an experiment's outcome: code version, data version, environment (OS, libraries), hyperparameters, random seeds, and hardware.

2. Design Versioning Scheme

Propose a versioning system for each component, such as Git for code, DVC or hash-based IDs for data, and containerization for environments.

3. Capture Metadata

Define metadata to track for each run: unique run ID, timestamps, user, parameters, metrics, and links to versioned artifacts.

4. Ensure Reproducibility

Describe how to reproduce a run: retrieve artifacts, rebuild environment, and re-execute with same inputs. Mention deterministic execution and seeding.

5. Address Trade-offs

Discuss trade-offs between storage cost, speed of reproduction, and completeness. Suggest strategies like caching, incremental versioning, and tiered storage.

Key Points to Mention

  • Version control for code (Git) and data (DVC, Git LFS, or hash-based storage)
  • Environment reproducibility via Docker containers or Conda environments with pinned dependencies
  • Configuration management using YAML/JSON files with versioned schemas
  • Random seed control and deterministic algorithms for exact reproducibility
  • Metadata tracking with tools like MLflow, Weights & Biases, or custom databases
  • Trade-offs: storage overhead vs. reproducibility guarantees, and strategies like content-addressable storage

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q3

How would this configuration system integrate with the actual training pipeline? Walk through the handoff from config definition to a running training job.

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

Kept it practical: config gets resolved and validated, serialized to a canonical format, passed to the job launcher which hydrates it into the trainer's argument namespace.

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AI HintsAI Generated

Suggested Approach

Structure your answer as a clear pipeline: start with config definition (schema, validation), then loading and parsing, then merging with defaults and overrides, then instantiation of training components, and finally launching the job with logging and reproducibility. Emphasize how each stage ensures correctness, flexibility, and observability.

Pro tip: Highlight the importance of config versioning and immutable snapshots for reproducibility—this shows you understand production ML systems, not just toy examples.

1. Config Definition and Schema

Define a typed schema (e.g., using Pydantic, dataclasses, or YAML with JSON Schema) that specifies all hyperparameters, paths, and resource requirements. This enables validation and auto-completion.

2. Loading and Validation

Load the config from a file or service, validate it against the schema, and apply any environment-specific overrides (e.g., via CLI args or env vars). Fail fast on invalid configs.

3. Merging and Resolution

Merge the user config with defaults and any dynamic overrides (e.g., from a hyperparameter tuning service). Resolve references (e.g., dataset paths) and produce a final, immutable config object.

4. Instantiation of Training Components

Use the resolved config to instantiate the model, optimizer, data loaders, and other components. Pass the config object to each component or use a factory pattern.

5. Job Launch and Logging

Launch the training job (e.g., via a scheduler like Kubernetes or Slurm), log the full config for reproducibility, and monitor the job. Ensure the config is saved alongside model checkpoints.

Key Points to Mention

  • Schema validation and type safety to catch errors early
  • Layered configuration: defaults, user overrides, environment-specific settings
  • Immutability and versioning of configs for reproducibility
  • Dependency injection or factory patterns to decouple config from code
  • Logging and tracking configs with experiment management tools (e.g., MLflow, Weights & Biases)
  • Error handling and fallback strategies for missing or invalid configs

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.