LangChain Streaming and API Integration

Streaming is a common pattern in AI applications. We've all seen AI interfaces where answers from AI chatbots appear on the screen as a word-by-word stream of information.

This word-by-word stream can look nice but provides many more benefits. Streamed text feels more natural to the user, which means the user can begin reading a response sooner.

The Time-to-First-Token of models like gpt-4.1-mini is very low (just 1-2 seconds in many cases). However, the full generation time (or Time-to-Last-Token, TTLT) can vary significantly. When generating long responses from gpt-4.1-mini, a TTLT of 10-20 seconds is typical.

A significant difference exists in having users wait 1-2 seconds vs 10-20 seconds. But beyond this, streaming also allows us to send intermediate steps to our interfaces. Suppose an agent uses various tools and/or takes multiple steps to generate a final response. In that case, we can use streaming to send this information to our application, allowing us to render UI components that inform the user about the agent's actions.

Using these intermediate step components, we provide continual feedback to the user, preventing them from being stuck staring at a blank screen. These components also provide us with an interface to provide more information to the user, such as research sources or results from intermediate calculations.

In this chapter, we will introduce LangChain's async streaming. Async streaming is an essential feature for APIs wanting to support real-time information streaming and enable the enhanced user experience described above.

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00:00 LangChain Streaming
00:54 Streaming for AI
06:08 Basic LangChain Streaming
10:16 Streaming with Agents
28:13 Custom Agent and Streaming
31:13 Streaming to an API