AI features are I/O-bound and long-running, which changes what you should optimise for when you pick a runtime and framework. The defaults that suit a CRUD app are not always the right ones here.
Runtime trade-offs
Node remains the safe default for its ecosystem and streaming support, while newer runtimes offer faster startup that matters at the edge. Choose based on library compatibility with your model SDKs rather than benchmarks.
Framework shape
A meta-framework such as Next.js couples your UI and API cleanly, but a dedicated backend with Fastify or Express gives you clearer control over streaming, timeouts and long-lived connections. Match the choice to how much server work you expect.
Concurrency reality
A single model call can occupy a connection for many seconds. Plan for many concurrent open requests, tune your server’s timeouts accordingly, and never block the event loop with synchronous work.
Action step
Sketch the runtime and framework choice for one AI feature you plan to build, listing the longest expected request duration and how many concurrent calls you must support.
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