Enum Event 

pub enum Event {
    MessageStart {
        message: Message,
    },
    ContentBlockStart {
        index: u32,
        content_block: ContentBlock,
    },
    ContentBlockDelta {
        index: u32,
        delta: Delta,
    },
    ContentBlockStop {
        index: u32,
    },
    MessageDelta {
        delta: MessageDelta,
        usage: Usage,
    },
    MessageStop,
    Ping,
    Error {
        error: Value,
    },
    Unknown,
}

One Anthropic streaming event.

Mirrors the messages streaming wire format as of late 2025. Unknown event types fall through to Event::Unknown so the parser never panics on a new event Anthropic adds.

Variants

MessageStart

Sent first; carries the response shell (id, role, model, initial usage).

Fields

message: Message

The shell message: id, role, model, etc.

ContentBlockStart

A new content block is starting (text, tool_use, thinking, etc.).

Fields

index: u32

Index in the message’s content array.

content_block: ContentBlock

The (initially empty) content block.

ContentBlockDelta

A delta extending an in-progress content block.

Fields

index: u32

Index in the message’s content array.

delta: Delta

What changed.

ContentBlockStop

A content block is complete.

Fields

index: u32

Index in the message’s content array.

MessageDelta

Top-level message delta (final stop_reason, usage so far, etc.).

Fields

delta: MessageDelta

What changed about the top-level message.

usage: Usage

Cumulative token usage.

MessageStop

Final event for a message.

Ping

Heartbeat keep-alive; ignore.

Error

Provider-side error; usually means the connection will close.

Fields

error: Value

Error payload as Anthropic sent it.

Unknown

Any event type we don’t know about. Forward-compatible escape hatch.

Trait Implementations

impl Clone for Event

fn clone(&self) -> Event

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Event

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Event

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Event

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

where __S: Serializer,

Serialize this value into the given Serde serializer.