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AI Interview Question

Design Qwen architecture for a coding copilot for a large engineering org

Model ProvidersHardScenario Based18 min read

Design a production coding copilot on self-hosted Qwen2.5-Coder: FIM inline completion vs chat models, vLLM serving with prefix caching, a 50M-chunk code index with ACLs, and evaluation.

Quick answer

I would split the copilot into two paths: a small Qwen2.5-Coder model for low-latency fill-in-the-middle completions in the IDE, and a larger Qwen coder or general instruct model for chat, explanations, and multi-file edits. Both run on vLLM with prefix caching and continuous batching, and a retrieval service over the 50 million chunks supplies relevant code, filtered by each developer's repository permissions. Success is measured with acceptance rate, latency, and offline execution-based tests, not just user sentiment.

The interview question

A large engineering org wants to move its internal coding copilot from a prototype to production using self-hosted Qwen models (for example Qwen2.5-Coder) with repository context drawn from about 50 million indexed code and documentation chunks. Design the architecture: model selection for inline completion versus chat, serving, retrieval, permissions, and evaluation. Explain your choices.

Deep explanation

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Model ProvidersOpen ModelsQwenSeniorArchitecture