Struct ChoiceDelta 

pub struct ChoiceDelta {
    pub content: Option<String>,
    pub reasoning_content: Option<String>,
    pub function_call: Option<ChoiceDeltaFunctionCall>,
    pub refusal: Option<String>,
    pub role: Option<CompletionRole>,
    pub tool_calls: Option<Vec<ChoiceDeltaToolCall>>,
    pub annotations: Option<Vec<Annotation>>,
    pub audio: Option<ChatCompletionAudio>,
}

Fields

content: Option<String>

The contents of the chunk message.

reasoning_content: Option<String>

The reasoning contents of the chunk message. Only present for thinking models (DeepSeek, Qwen3, and other reasoning models served by OpenAI-compatible backends).

function_call: Option<ChoiceDeltaFunctionCall>

Deprecated and replaced by tool_calls.

The name and arguments of a function that should be called, as generated by the model.

refusal: Option<String>

The refusal message generated by the model.

role: Option<CompletionRole>

The role of the author of this message.

tool_calls: Option<Vec<ChoiceDeltaToolCall>>

A list of tool calls generated by the model, such as function calls.

annotations: Option<Vec<Annotation>>

Annotations for the chunk message, such as URL citations emitted by search deployments.

Not part of the official OpenAI chunk schema, but Azure OpenAI (“on your data” / search deployments) streams annotations inside delta, and dropping them silently loses the citations.

audio: Option<ChatCompletionAudio>

Data about a streamed audio response from the model.

Not part of the official OpenAI chunk schema, but audio-capable Azure OpenAI deployments stream audio inside delta.

Trait Implementations

impl Clone for ChoiceDelta

fn clone(&self) -> ChoiceDelta

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ChoiceDelta

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for ChoiceDelta

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for ChoiceDelta

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

where __S: Serializer,

Serialize this value into the given Serde serializer.