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

SeniorPrefer not to say
Apr 2026

Summary

System design round at OpenAI for a SWE role, centered entirely on architecting a GPT-3 Playground from scratch. Pretty open-ended, which I wasn't fully prepared for.

Questions Asked (4)

Q1

Design the high-level architecture for a GPT-3 Playground website from scratch, covering backend data organization, frontend state management, streaming responses, parameter controls, and saved presets.

System DesignAPI & IntegrationsData Modeling
Author's notes

This was the whole interview, basically one giant open-ended prompt.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then present a high-level architecture that separates concerns: frontend (React with state management), backend (API gateway, orchestration, data stores), and streaming infrastructure. Focus on how streaming responses are handled end-to-end, how parameters and presets are managed, and how data is organized for scalability and low latency.

Pro tip: Emphasize trade-offs and failure modes, such as handling streaming interruptions, rate limiting, and cost controls, to show you think beyond the happy path. Also, mention observability and monitoring as key components of the architecture.

1. Clarify Requirements and Scale

Ask about expected traffic, latency requirements, and key features (e.g., real-time streaming, preset sharing). This ensures the design meets actual needs and demonstrates thoroughness.

2. High-Level Architecture Overview

Sketch the main components: frontend (React SPA), backend (API gateway, orchestration service, model inference service), data stores (for presets, user data, logs), and streaming infrastructure (WebSockets or SSE). Explain how they interact.

3. Frontend State Management and Streaming

Describe how the frontend manages state (e.g., Redux, Zustand, or React Context) for parameters, conversation history, and streaming responses. Explain how streaming data is received (e.g., SSE) and incrementally rendered.

4. Backend Data Organization and Presets

Detail the data models for users, presets, and conversations. Discuss storage choices (e.g., PostgreSQL for relational data, Redis for caching) and how presets are saved, retrieved, and shared.

5. Parameter Controls and API Design

Explain how parameter controls (temperature, max tokens, etc.) are exposed in the UI and passed to the backend. Discuss API endpoints for completions, streaming, and preset management, including validation and rate limiting.

Key Points to Mention

  • Use Server-Sent Events (SSE) or WebSockets for streaming responses, with fallback to polling if needed.
  • Frontend state management should handle optimistic updates and streaming chunks without blocking the UI.
  • Data modeling: presets as JSON blobs with metadata, conversations stored with messages and parameters.
  • Parameter controls should be validated on both client and server, with sensible defaults and constraints.
  • Scalability: use a message queue (e.g., Kafka) to decouple request ingestion from model inference, and cache frequent presets.
  • Security: authentication, authorization for presets, and rate limiting to prevent abuse.

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

Q2

How would you organize and model the backend data for this system, including prompts, model parameters, and user-saved presets?

Data ModelingSystem DesignTechnical Trade-offs
Author's notes

I went straight to a relational schema and they seemed fine with it, but I didn't think through the versioning angle for presets until they pushed back.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the core entities and their relationships, then propose a normalized schema with appropriate indexes and constraints. Discuss how to handle versioning, access control, and scalability, and justify trade-offs between flexibility and performance.

Pro tip: Emphasize idempotency and auditability for prompts and presets, and mention how you'd handle schema evolution without breaking existing clients—this shows you think about production realities.

1. Identify core entities and relationships

Define the main objects: users, prompts, model parameters, presets, and their associations. Clarify cardinality (e.g., one user has many presets, a preset references a prompt and parameters).

2. Design normalized schema with constraints

Propose tables/collections with primary keys, foreign keys, and indexes. Include fields like prompt text, parameter name/value pairs, and preset metadata. Enforce uniqueness and referential integrity.

3. Address versioning and auditability

Explain how to track changes to prompts and presets (e.g., version columns, history tables). Discuss soft deletes and timestamps for audit trails.

4. Plan for access control and multi-tenancy

Describe how to scope data per user or organization, including row-level security or tenant IDs. Mention sharing and permission models for presets.

5. Discuss scalability and trade-offs

Compare SQL vs NoSQL, denormalization for read performance, caching strategies, and sharding. Justify choices based on expected query patterns and scale.

Key Points to Mention

  • Entity-relationship modeling with clear primary and foreign keys
  • Indexing strategies for frequent queries (e.g., user_id, preset_name)
  • Versioning and audit trails for prompts and presets
  • Access control and multi-tenancy considerations
  • Trade-offs between normalization and denormalization
  • Schema evolution and backward compatibility

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

Q3

How would you handle streaming the GPT-3 model response to the frontend in real time?

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

Blanked a little here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements such as latency, scale, and client constraints. Then describe an end-to-end architecture using streaming protocols like Server-Sent Events (SSE) or WebSockets, covering how the model's token stream is chunked and delivered to the frontend. Finally, discuss trade-offs and optimizations for real-time performance and reliability.

Pro tip: Mention that OpenAI's own API uses SSE for streaming, and highlight the importance of handling backpressure and connection drops gracefully to ensure a smooth user experience.

1. Clarify Requirements and Constraints

Ask about expected latency, number of concurrent users, client types (web, mobile), and whether partial responses are acceptable. This ensures your solution aligns with the actual needs.

2. Choose a Streaming Protocol

Compare SSE, WebSockets, and HTTP chunked transfer. Explain why SSE is often ideal for one-way server-to-client streaming, but WebSockets may be needed for bidirectional communication.

3. Design the Backend Architecture

Describe how the backend receives the stream from the GPT-3 API (e.g., via HTTP streaming), processes chunks, and forwards them to the frontend. Include load balancing, connection management, and scaling considerations.

4. Implement Frontend Handling

Explain how the frontend consumes the stream (e.g., using EventSource for SSE or WebSocket API), updates the UI incrementally, and handles errors or reconnections.

5. Address Trade-offs and Optimizations

Discuss trade-offs like latency vs. throughput, buffering strategies, backpressure, and fallback mechanisms. Mention monitoring and testing for real-time performance.

Key Points to Mention

  • Server-Sent Events (SSE) vs. WebSockets: when to use each
  • HTTP/2 and multiplexing benefits for streaming
  • Token chunking and incremental rendering on the frontend
  • Handling backpressure and flow control
  • Error handling, reconnection, and fallback to polling
  • Scalability considerations: load balancers, connection limits, and stateless services

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

Q4

How would you manage UI state and handle user interactions like changing model parameters and submitting prompts?

System DesignTechnical Trade-offs
Author's notes

This part went better.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, such as the complexity of the UI, real-time needs, and scalability. Then propose a state management architecture that separates concerns (e.g., local vs. global state) and describe how you would handle user interactions with debouncing, optimistic updates, and error handling. Finally, discuss trade-offs between different approaches and justify your choices based on the context.

Pro tip: Demonstrate awareness of OpenAI's specific challenges, such as handling streaming responses and rate limiting, by mentioning how you would manage partial updates and backpressure in the UI. Also, emphasize the importance of accessibility and responsiveness in a high-traffic application.

1. Clarify Requirements

Ask questions to understand the scope: expected number of parameters, frequency of updates, need for real-time feedback, and whether the UI is for internal or external users. This shows you don't jump to solutions without context.

2. Choose State Management Strategy

Decide between local component state, global state (e.g., Redux, Zustand), or server state (e.g., React Query). Explain how you'd handle form state for model parameters and prompt input, considering performance and developer experience.

3. Handle User Interactions

Describe how you'd manage parameter changes (e.g., debouncing, validation) and prompt submission (e.g., optimistic UI, loading states, error handling). Mention techniques like throttling for sliders and disabling submit during in-flight requests.

4. Manage Asynchronous Updates

Explain how you'd handle streaming responses from the API, such as using WebSockets or server-sent events, and updating the UI incrementally. Discuss state synchronization and avoiding race conditions.

5. Discuss Trade-offs and Scalability

Compare approaches (e.g., controlled vs. uncontrolled components, global vs. local state) and justify your choices. Mention performance optimizations like memoization, virtualization, and code splitting.

Key Points to Mention

  • State management libraries (e.g., Redux, Zustand, React Query) and their appropriate use cases
  • Debouncing and throttling for parameter changes to reduce API calls and improve performance
  • Optimistic UI updates and loading states for prompt submission to enhance user experience
  • Handling streaming responses and partial updates (e.g., using WebSockets or SSE)
  • Error handling and retry mechanisms for failed requests
  • Accessibility and responsiveness considerations in a high-traffic application

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