Struct StreamChunk 

pub struct StreamChunk {
    pub text: String,
    pub thinking_content: Option<String>,
    pub token_usage: Option<TokenUsage>,
    pub tool_calls: Option<Vec<ToolCall>>,
}

A single streaming chunk emitted by BaseChatModel::stream_chat.

Replaces the bare String chunk so streaming paths can observe token usage without a separate non-streaming invoke. Most providers only populate StreamChunk::token_usage on the final chunk; intermediate chunks carry text with token_usage: None. Providers that do not report usage (Ollama, local, proxy passthrough) always yield token_usage: None.

0.20.0 S3.2: StreamChunk::tool_calls carries the complete tool calls requested by the model, accumulated from the provider’s streaming tool_calls deltas. OpenAI-family providers (OpenAI / Azure / their delegates) attach them to the terminal chunk — the usage chunk, or a dedicated tool-calls chunk when the stream ends without usage; providers without streaming tool-call support always yield None. Consumers that only stream text can ignore the field.

Fields

text: String

The text delta for this chunk.

thinking_content: Option<String>

Model’s chain-of-thought / reasoning delta for this chunk, when the provider exposes one on a separate channel (DeepSeek reasoning_content, Anthropic thinking, Cohere thinking…). 0.25.0: previously the field existed on some raw provider types but was dropped on the way to BaseChatModel::stream_chat.

token_usage: Option<TokenUsage>

Token usage for the whole streaming call, typically only on the last chunk (when the provider reports it).

tool_calls: Option<Vec<ToolCall>>

Complete tool calls requested by the model in this streaming call, if any. 0.20.0 S3.2: filled on the terminal chunk by providers that support streaming tool_calls (OpenAI / Azure and their delegates); None otherwise.

Implementations

impl StreamChunk

pub fn new(text: impl Into<String>) -> Self

Creates a text-only chunk with no token usage and no tool calls.

Trait Implementations

impl Clone for StreamChunk

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for StreamChunk

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

Formats the value using the given formatter.

impl Default for StreamChunk

fn default() -> Self

Returns the “default value” for a type.