Enum AgentStreamEvent 

pub enum AgentStreamEvent {
    Text {
        content: String,
    },
    ToolCall {
        state: ToolCallState,
    },
    ToolStart {
        name: String,
        input: String,
    },
    ToolEnd {
        name: String,
        output: String,
    },
    PipelineStep {
        step: String,
        detail: Option<String>,
    },
    FinalAnswer {
        content: String,
    },
    Error {
        message: String,
    },
}

Agent streaming event

Variants

Text

LLM output text (token)

Fields

content: String

Output text content

ToolCall

Tool-call state change (Function Calling style)

Fields

state: ToolCallState

Tool-call state

ToolStart

ReAct-style tool call start

Fields

name: String

Tool name

input: String

Tool input

ToolEnd

ReAct-style tool call completion

Fields

name: String

Tool name

output: String

Tool output

PipelineStep

Pipeline step event (for RAG/research agents). Indicates which stage of the pipeline is currently executing.

Fields

step: String

Step name (e.g., “retrieving”, “grading”, “generating”, “planning”, “searching”, “synthesizing”).

detail: Option<String>

Optional detail message.

FinalAnswer

Final answer

Fields

content: String

Final answer content

Error

Streaming execution error

Fields

message: String

Error message

Trait Implementations

impl Clone for AgentStreamEvent

fn clone(&self) -> AgentStreamEvent

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for AgentStreamEvent

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Runnable<String, AgentStreamEvent> for AgentEventRunnable

type Error = LcelError

Error type.

fn invoke<'life0, 'async_trait>( &'life0 self, input: String, config: Option<RunnableConfig>, ) -> Pin<Box<dyn Future<Output = Result<AgentStreamEvent, LcelError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Transforms single input to output.

fn stream<'life0, 'async_trait>( &'life0 self, input: String, _config: Option<RunnableConfig>, ) -> Pin<Box<dyn Future<Output = Result<Pin<Box<dyn Stream<Item = Result<AgentStreamEvent, LcelError>> + Send>>, LcelError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Streaming output - for real-time responses (LLM, etc).

fn batch<'life0, 'async_trait>( &'life0 self, inputs: Vec<Input>, config: Option<RunnableConfig>, ) -> Pin<Box<dyn Future<Output = Result<Vec<Output>, Self::Error>> + Send + 'async_trait>>

where 'life0: 'async_trait, Self: 'async_trait,

Batch processing - transforms multiple inputs to outputs.

fn batch_as_completed<'life0, 'async_trait>( &'life0 self, inputs: Vec<Input>, config: Option<RunnableConfig>, ) -> Pin<Box<dyn Future<Output = Result<Vec<(usize, Output)>, Self::Error>> + Send + 'async_trait>>

where 'life0: 'async_trait, Self: 'async_trait,

Batch processing that returns results in completion order.

fn transform<'life0, 'async_trait>( &'life0 self, input: Pin<Box<dyn Stream<Item = Result<Input, Self::Error>> + Send>>, config: Option<RunnableConfig>, ) -> Pin<Box<dyn Future<Output = Result<Pin<Box<dyn Stream<Item = Result<Output, Self::Error>> + Send + 'life0>>, Self::Error>> + Send + 'async_trait>>

where 'life0: 'async_trait, Self: 'async_trait,

Stream-to-stream transformation - the core of LCEL streaming.