Type Alias EventStream 

pub type EventStream = Pin<Box<dyn Stream<Item = Result<StreamEvent>> + Send>>;

A pinned, boxed stream of events from the model.

This type alias represents an asynchronous stream that yields StreamEvent items. Each item is wrapped in a Result to handle potential errors during streaming.

The stream is:

• Pinned (Pin<Box<...>>): Required for safe async operations and self-referential types
• Boxed: Allows dynamic dispatch and hides the concrete stream implementation
• Send: Can be safely transferred between threads

Events

• StreamEvent::Block: one ContentBlock — a fragment of assistant text as it arrives, or a fully assembled tool call
• StreamEvent::Reasoning: chain-of-thought text, only when AgentOptions::include_reasoning is enabled
• StreamEvent::Finish: exactly once, as the final item, carrying the FinishReason

Migrating from ContentStream (0.7.x and earlier)

The stream used to yield bare ContentBlocks. Wrap the old match in StreamEvent::into_block to get the previous behaviour, then handle StreamEvent::Finish where the distinction between a clean stop and a truncated response matters.

Error Handling

Errors in the stream indicate issues like:

• Network failures or timeouts
• Malformed SSE events
• JSON parsing errors
• API errors from the model provider

When an error occurs, the stream typically terminates. It’s the caller’s responsibility to handle errors appropriately.

Examples

use open_agent::{query, AgentOptions, ContentBlock, FinishReason, StreamEvent};
use futures::StreamExt;

let options = AgentOptions::builder()
    .model("gpt-4")
    .api_key("sk-...")
    .build()?;

let mut stream = query("Hello!", &options).await?;

while let Some(result) = stream.next().await {
    match result? {
        StreamEvent::Block(ContentBlock::Text(text)) => print!("{}", text.text),
        StreamEvent::Finish(reason) => println!("\nstopped: {reason}"),
        _ => {}
    }
}

Aliased Type

pub struct EventStream { /* private fields */ }