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Xai·Software Engineer·Take-home Assignment·Senior

Senior
Apr 2026

Summary

Xai had me do a take-home style coding exercise where I had to build a small LLM API wrapper from scratch. The scope was bigger than I expected and the discussion afterward got pretty deep into design decisions.

Questions Asked (3)

Q1

Build a small library that calls an LLM API endpoint with configurable parameters like model, temperature, top_p, max_tokens, and stop sequences. It should handle retries with backoff, rate limiting, prompt batching, async and streaming responses, and structured logging.

API & IntegrationsSystem DesignTechnical Trade-offs
Author's notes

This was a lot more surface area than I budgeted time for.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then outline a modular architecture that separates concerns like API client, retry logic, rate limiting, batching, and logging. Discuss trade-offs for each component and how they integrate, emphasizing configurability, scalability, and observability.

Pro tip: Mention that you would use exponential backoff with jitter and respect the Retry-After header to avoid thundering herd problems, and that you'd implement rate limiting with a token bucket algorithm to smooth out bursts.

1. Clarify Requirements and Constraints

Ask about expected throughput, latency requirements, error handling expectations, and whether the library needs to support multiple LLM providers. This ensures the design meets actual needs.

2. Design Core Components

Outline modules: a configurable client for API calls, a retry handler with backoff, a rate limiter, a batcher, and a logger. Explain how they interact and the interfaces between them.

3. Address Key Features

Detail implementation strategies for retries (exponential backoff with jitter), rate limiting (token bucket), batching (grouping prompts by size/time), async/streaming (using async generators), and structured logging (JSON logs with context).

4. Discuss Trade-offs and Edge Cases

Compare approaches for each feature, such as fixed vs exponential backoff, client-side vs server-side rate limiting, and how to handle partial failures in batching. Mention idempotency and error propagation.

5. Summarize and Extend

Recap the design, highlight how it meets requirements, and suggest potential extensions like caching, circuit breakers, or metrics integration for production readiness.

Key Points to Mention

  • Configurable parameters: model, temperature, top_p, max_tokens, stop sequences, with validation and defaults.
  • Retry logic: exponential backoff with jitter, max retries, and handling of retryable vs non-retryable errors.
  • Rate limiting: token bucket or leaky bucket algorithm, with configurable rate and burst capacity.
  • Prompt batching: grouping multiple prompts into a single API call when supported, with considerations for token limits and latency.
  • Async and streaming: using async/await for concurrency and async generators for streaming responses, with proper error handling.
  • Structured logging: JSON logs with request IDs, timestamps, latency, and error details for observability.

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

Q2

Walk through your API design choices for the library and explain how you'd integrate it into a larger production application.

API & IntegrationsSystem DesignTechnical Trade-offs
Author's notes

They pushed pretty hard on the integration story.

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AI HintsAI Generated

Suggested Approach

Start by framing your API design around the core use cases and constraints of the library, then walk through key decisions like abstraction level, error handling, and extensibility. Finally, explain how you would integrate it into a production system, covering dependency management, configuration, observability, and scaling considerations.

Pro tip: Show that you think about API design as a product: consider developer experience, versioning, and backward compatibility from day one. Also, mention how you'd gather feedback and iterate on the API based on real-world usage.

1. Clarify requirements and constraints

Briefly restate the library's purpose and the key constraints (e.g., performance, ease of use, target users) that shaped your API design.

2. Explain core API design choices

Discuss decisions like function signatures, data models, error handling, and extensibility points, and justify them with trade-offs.

3. Address integration into a larger app

Describe how the library would be consumed: dependency injection, configuration, logging, monitoring, and testing within a production environment.

4. Highlight production concerns

Cover aspects like performance, scalability, security, versioning, and how you'd handle breaking changes or deprecations.

5. Summarize and reflect

Wrap up by reiterating the most important design principles and how they enable smooth integration and long-term maintainability.

Key Points to Mention

  • Abstraction level: balancing simplicity for users vs. flexibility for advanced use cases
  • Error handling strategy: exceptions vs. result types, and how errors propagate to the caller
  • Extensibility: plugin architecture, hooks, or interfaces for customization
  • Dependency management: how the library is packaged, versioned, and included in a larger app
  • Observability: logging, metrics, and tracing integration for production monitoring
  • Backward compatibility and versioning: semantic versioning, deprecation policies, and migration guides

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

Q3

How did you approach error handling across the different failure modes, and what tradeoffs did you make?

Technical Trade-offsAPI & Integrations
Author's notes

Honestly the question I felt best about.

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AI HintsAI Generated

Suggested Approach

Start by categorizing the failure modes you encountered (e.g., transient, permanent, partial) and explain how you mapped each to a specific handling strategy. Then discuss the tradeoffs you made between reliability, complexity, latency, and cost, using concrete examples to illustrate your reasoning.

Pro tip: Quantify the impact of your tradeoffs—e.g., 'We accepted a 0.1% increase in error rate to reduce p99 latency by 200ms'—to show you think in terms of measurable outcomes. Also, mention how you validated your error handling through chaos testing or fault injection.

1. Categorize failure modes

Identify and classify the different types of failures you anticipated or encountered, such as transient network errors, permanent validation errors, or partial system outages.

2. Define handling strategies

For each failure category, describe the specific error handling techniques you applied, such as retries with exponential backoff, circuit breakers, fallbacks, or fail-fast validation.

3. Explain tradeoffs

Discuss the tradeoffs involved in your choices, such as increased complexity vs. improved resilience, added latency vs. consistency, or cost vs. reliability.

4. Share concrete examples

Provide a specific instance where your error handling made a difference, including the problem, your solution, and the measurable outcome.

5. Reflect on lessons learned

Summarize what you would do differently or how you iterated on your approach based on monitoring, incidents, or feedback.

Key Points to Mention

  • Retry strategies with exponential backoff and jitter for transient failures
  • Circuit breakers and bulkheads to prevent cascading failures
  • Idempotency and exactly-once semantics for safe retries
  • Fallback mechanisms and graceful degradation
  • Observability: logging, metrics, and tracing to detect and diagnose failures
  • Tradeoffs between consistency, availability, latency, and cost

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