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# Streaming AI Responses in Real-Time with SSE in Next.js & NestJS

Rendering an AI response under 120ms boosts retention by 30%. Learn to build lightning-fast, real-time SSE streams using Next.js and NestJS to slash LLM costs.

- **Speakers:** [Ahmed Megahd](https://www.wearedevelopers.com/@ahmed-megahd)
- **Event:** World Congress 2025
- **Published:** August 20, 2025
- **Duration:** 29:54
- **URL:** https://www.wearedevelopers.com/videos/1630-streaming-ai-responses-in-real-time-with-sse-in-next-js-nestjs

## Summary

Modern AI applications require interactive, real-time responses rather than sluggish, traditional request-response cycles. Implementing Server-Sent Events (SSE) establishes a lightweight, unidirectional communication channel that pushes data directly to the client, utilizing roughly half the memory of server-heavy bidirectional WebSockets. By significantly reducing the time to first token, developers can dramatically improve user experience; rendering an initial response within 120 milliseconds can increase user retention by up to 30 percent by mimicking the psychological engagement of continuous processing.

Building this streaming architecture relies on native web APIs and straightforward back-end integrations. In a Next.js front end, developers leverage the natively supported EventSource API to capture incoming text chunks and simulate an engaged typewriter effect. Concurrently, NestJS serves as the back-end anchor managing these active SSE endpoints alongside platform providers like OpenAI, which natively streams token-by-token, and Gemini, which operates chunk-by-chunk. By carefully tracking aborted requests and actively closing streaming connections when users disconnect mid-generation, engineering teams can prevent unused generation loops and save up to 25 percent on overall LLM infrastructure costs.

Scaling SSE infrastructures requires deliberate operational foresight as concurrent connections climb. For production deployments handling thousands of simultaneous user sessions, developers must disable Nginx reverse proxy buffering to ensure data chunks push instantly without delay. As user traffic grows, implementing Redis streams or dedicated hub queuing mechanisms handles auto-reconnection efficiently, seamlessly distributing complex state changes—such as custom GPT interactions or multi-device push notifications—across mobile apps, browser extensions, and web dashboards.

**Keywords:** server-sent events, real-time ai streaming, nextjs eventsource api, nestjs sse implementation, time to first token, websocket memory comparison, openai token streaming, gemini chunk streaming, nginx proxy buffering, redis stream queuing, unidirectional data push, llm cost optimization, typewriter effect ui, custom gpt synchronization, user retention optimization

## Chapters

1. **Improving user retention with real-time AI response streaming** (00:00) — Streaming AI responses reduces wait times and significantly increases user engagement in applications.
1. **Comparing protocols for real-time client and server communication** (04:14) — Server-sent events provide a memory-efficient, unidirectional alternative to WebSockets and REST for pushing data.
1. **Full stack architecture for server-sent events using Next.js** (06:28) — Native browser APIs and backend frameworks enable seamless data streaming while integrating authentication and rate limiting.
1. **Implementing streaming endpoints for OpenAI and Gemini models** (09:20) — Configuring proxy headers and utilizing provider SDKs ensures reliable chunk-by-chunk delivery to the client.
1. **Handling client-side connection states and dynamic UI updates** (12:42) — Managing event source connections correctly simulates typewriter effects and saves token costs by stopping canceled requests.
1. **Broadcasting notifications and managing active client connection lists** (14:57) — Tracking active subscriber connections enables targeted message distribution across multiple devices simultaneously.
1. **Scaling server-sent events with external queues and monitoring** (19:44) — Implementing keep-alive pings and Redis streams supports high concurrency and load balancing across server instances.
1. **Evaluating AI provider streaming speeds and generation formats** (23:45) — Choosing between token-by-token or chunked delivery methods impacts how text is rendered in the interface.
1. **Synchronizing custom GPT models across multiple application platforms** (26:10) — Real-time event pushes enable seamless data transfers from external AI tools to internal dashboards and extensions.
1. **Choosing the right communication protocol for real-time needs** (28:30) — Unidirectional server-sent events optimize resources for push payloads where bidirectional WebRTC or gRPC are unnecessary.

## Related Moments

- [Implementing an AI backend streaming integration in javascript](https://www.wearedevelopers.com/videos/905-leveraging-server-sent-events-sse-for-efficient-data-streaming-in-ui-development) (from "Leveraging Server-Sent Events (SSE) for Efficient Data Streaming in UI Development")
- [Leveraging server-side streaming for performance and interactivity](https://www.wearedevelopers.com/videos/1302-wearedevelopers-live-dishonest-charts-britcss-debugging-with-ai) (from "WeAreDevelopers LIVE - Dishonest Charts, BritCSS, Debugging with AI")
- [Why generative AI revived the Server-Sent Events protocol](https://www.wearedevelopers.com/videos/905-leveraging-server-sent-events-sse-for-efficient-data-streaming-in-ui-development) (from "Leveraging Server-Sent Events (SSE) for Efficient Data Streaming in UI Development")
- [Integrating OpenAI for real-time streaming responses](https://www.wearedevelopers.com/videos/1736-minimal-infrastructure-for-real-time-phone-agents-transcripts-in-responses-out) (from "Minimal infrastructure for Real‑Time Phone Agents: transcripts in, responses out")
- [Building agentic artificial intelligence applications using Node.js](https://www.wearedevelopers.com/videos/1512-building-ai-applications-with-langchain-and-node-js) (from "Building AI Applications with LangChain and Node.js")
- [Optimizing system scalability and real-time push capabilities](https://www.wearedevelopers.com/videos/494-the-rise-of-reactive-microservices) (from "The Rise of Reactive Microservices")

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