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DeepSeek R2 is expected around August 2025 with improvements over R1 in reasoning, code generation, and an expanded 256K context window. This guide helps JavaScript/Node.js developers prepare their stacks before release by building model-agnostic LLM abstractions, SSE streaming infrastructure, feature flags for gradual rollout, and evaluation harnesses using R1 as a baseline. Practical code examples cover a provider-agnostic LLM client, an Express SSE chat route, a React streaming frontend, a traffic-splitting model router, and an eval runner script. The core argument is that model-agnostic architecture means migrating to R2 becomes a config change rather than a rewrite, and the preparation is valuable regardless of whether R2 ships on schedule.