Enum StreamEvent 

#[non_exhaustive]
pub enum StreamEvent {
    Delta(String),
    ToolCall {
        id: String,
        name: String,
        arguments: String,
    },
    Reasoning(String),
    Done {
        reason: FinishReason,
        usage: Option<Usage>,
    },
}

An event in a streamed conversation reply.

One streamed reply = several StreamEvent::Delta / StreamEvent::ToolCall increments + one closing StreamEvent::Done; the caller concatenates the Deltas in order to get the full reply.

Stream termination semantics: on normal termination Done is always the last success event on the stream; errors terminate the stream with an Err item, and no events are produced after the error item.

The enum is #[non_exhaustive] (reserved for extension): matches must include a wildcard arm.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Delta(String)

An incremental fragment of the reply content.

ToolCall

The model requests a tool call; argument fragments have already been aggregated by the Provider into full JSON text, with fields matching crate::ToolCall so the Agent can use them directly.

Fields

id: String

Unique id of this call; the execution result is paired back to it via this id.

name: String

Tool name, corresponding to the name in Tool::schema.

arguments: String

Arguments generated by the model (JSON text).

Reasoning(String)

An incremental fragment of the model’s reasoning (thinking); the vendor delivers it in fragments during the stream, and the Provider forwards each fragment as it arrives (like StreamEvent::Delta) — consumers concatenate them in order to get the full text.

Corresponds to the reasoning field of Message; the Agent must store it in this turn’s message and carry it back verbatim in the history (otherwise thinking models like DeepSeek / Qwen3 reject the request).

Done

The model finished its reply; the stream produces no more events after this.

Fields

reason: FinishReason

Why the model ended its reply.

usage: Option<Usage>

Token usage for this turn; None when the endpoint did not return it (include_usage off or unsupported by the endpoint).

Trait Implementations

impl Clone for StreamEvent

fn clone(&self) -> StreamEvent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for StreamEvent

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for StreamEvent

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for StreamEvent

impl PartialEq for StreamEvent

fn eq(&self, other: &StreamEvent) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for StreamEvent

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for StreamEvent