Designing Streaming State Machines for Real-Time AI User Interfaces

Handling Asynchronous Latency with Grace

Integrating Large Language Models and generative GPU synthesis tasks into web interfaces introduces unique UX challenges. Unlike traditional REST APIs with sub-200ms roundtrips, generative pipelines can take several seconds to compute.

type StreamingState =
  | { status: "idle" }
  | { status: "connecting" }
  | { status: "streaming"; chunk: string; progress: number }
  | { status: "complete"; result: string }
  | { status: "error"; message: string }

Server-Sent Events over WebSockets

For unidirectional data generation (such as streaming text or queue status updates), Server-Sent Events (SSE) offer significant advantages over WebSockets:

• Built-in HTTP/2 multiplexing support.
• Native browser reconnection handling via EventSource.
• Seamless compatibility with edge serverless functions without stateful server socket pooling.

Reassuring Interaction Design

Never leave users staring at an uninformative spinner. Displaying granular pipeline phases ("Synthesizing vector embeddings", "Sampling diffusion steps") reassures users and dramatically reduces perceived waiting time.