Enum StreamDelta 

#[non_exhaustive]
pub enum StreamDelta {
    Start {
        id: String,
        model: String,
        provider_echoes: Vec<ProviderEchoSnapshot>,
    },
    TextDelta {
        text: String,
        provider_echoes: Vec<ProviderEchoSnapshot>,
    },
    ThinkingDelta {
        text: String,
        provider_echoes: Vec<ProviderEchoSnapshot>,
    },
    ToolUseStart {
        id: String,
        name: String,
        provider_echoes: Vec<ProviderEchoSnapshot>,
    },
    ToolUseInputDelta {
        partial_json: String,
    },
    ToolUseStop,
    Usage(Usage),
    RateLimit(RateLimitSnapshot),
    Warning(ModelWarning),
    Stop {
        stop_reason: StopReason,
    },
}

One chunk from a streaming model response.

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.

Start

First message — vendor’s response id and model identifier.

Fields

id: String

Vendor message id (echoed in the final ModelResponse).

model: String

Resolved model identifier.

provider_echoes: Vec<ProviderEchoSnapshot>

Response-level vendor opaque round-trip tokens — OpenAI Responses Response.id (so the next request can chain via previous_response_id from ModelRequest::continued_from), or anything else the codec wants to carry at response root rather than on a single content part. The aggregator surfaces these on ModelResponse::provider_echoes at finalize time, mirroring the non-streaming decode path.

TextDelta

Append text to the in-progress text block. Consecutive TextDeltas fold into a single ContentPart::Text in the output.

Fields

text: String

Text fragment to append.

provider_echoes: Vec<ProviderEchoSnapshot>

Vendor opaque round-trip tokens this fragment carries (Gemini 3.x attaches thought_signature to text parts on reasoning turns). The aggregator extends the open-text block’s accumulated echoes — a single ContentPart::Text finalises with the union of every delta’s echoes.

ThinkingDelta

Append text (or vendor opaque tokens) to the in-progress thinking block. Consecutive ThinkingDeltas fold into a single ContentPart::Thinking in the output. A delta carrying only provider_echoes (empty text) attaches the round-trip marker without growing the body — Anthropic emits the signature on a discrete signature_delta SSE event with no associated text.

Fields

text: String

Text fragment to append. Empty when the delta carries only a provider_echoes update.

provider_echoes: Vec<ProviderEchoSnapshot>

Vendor opaque round-trip tokens (Anthropic signature, Gemini thought_signature, OpenAI Responses encrypted_content). Codecs pre-wrap the wire-shape blob into ProviderEchoSnapshot before yielding the delta; the aggregator stays codec-agnostic and just accumulates.

ToolUseStart

Begin a new tool-use block. Closes any open text block so the output preserves the model’s intended ordering.

Fields

id: String

Stable tool-use id.

name: String

Tool name to call.

provider_echoes: Vec<ProviderEchoSnapshot>

Vendor opaque round-trip tokens attached to this tool call (Gemini 3.x thought_signature on functionCall parts — missing on the next turn yields HTTP 400 on the first functionCall of a step).

ToolUseInputDelta

Append partial JSON to the open tool-use block’s input buffer.

Fields

partial_json: String

Raw JSON fragment — the aggregator concatenates and parses once the block closes.

ToolUseStop

Close the current tool-use block. Returns Err if the buffered JSON does not parse.

Usage(Usage)

Token usage update (last value wins).

RateLimit(RateLimitSnapshot)

Provider rate-limit snapshot, typically emitted as the leading chunk by ChatModel::stream_deltas before the first content delta. Last value wins inside an aggregator.

Warning(ModelWarning)

Provider warning surfaced inline.

Stop

End of stream with stop reason.

Fields

stop_reason: StopReason

Reason the model halted.

Trait Implementations

impl Clone for StreamDelta

fn clone(&self) -> StreamDelta

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for StreamDelta

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

Formats the value using the given formatter.

impl PartialEq for StreamDelta

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for StreamDelta

impl StructuralPartialEq for StreamDelta