Send Message (Streaming)

Sends a new message to an existing chat and returns a Server-Sent Events stream. Events include the initial assistant-message snapshot, content chunk deltas, final usage, and a closing message snapshot. The response is `text/event-stream`; each event is `data: <JSON>\n\n` where the JSON conforms to MessageStreamEvent.

POST/v2/chats/{chatId}/messages/stream

Usage

TypeScript Example

import { v0 } from 'v0-sdk'const result = await v0.messages.sendStream({  chatId: 'chat_abc123',  message: 'Hello, world!',})console.log(result)

API Signature

Request

Path Parameters

chatId: string

The unique identifier of the chat.

Request Body

message: string

The prompt or instruction to send to the model.

systemPrompt?: string

System-level context for the chat, such as frameworks or development environment details.

modelConfiguration?: object

Overrides for the model behavior.

modelId: 'v0-auto' | 'v0-mini' | 'v0-pro' | 'v0-max' | 'v0-max-fast'

Model to use for the generation.

imageGenerations: boolean

Enables image generations to generate up to 5 images per version.

mcpServerIds?: string[]

MCP server IDs to enable. When omitted, uses default enabled servers.

attachments?: object[]

Files or assets to include with the message.

url: string

URL of the attachment.

skillIds?: string[]

Skill IDs (from skills.sh) to attach. Skills provide domain-specific knowledge to the AI. Maximum 3.

action?: object

An optional action. Use fix-with-v0 to trigger automatic error fixing — the message should contain the error context.

type: 'fix-with-v0'

Response (Stream)

The response is a text/event-stream. Each event is data: <JSON>\n\n where the JSON conforms to one of the following event types:

event: 'message' | 'message.parts.chunk' | 'message.usage' | 'error'

A single Server-Sent Events payload emitted by the streaming send-message endpoint. Each SSE event is data: <JSON>\n\n where the JSON conforms to one of the union members.

id: string

Unique message identifier.

chatId: string

ID of the chat this message belongs to.

role: 'user' | 'assistant'

Who produced this message.

createdAt: string

ISO timestamp when the message was created.

updatedAt: string

ISO timestamp when the message was last updated.

content: string

The trailing prose of the message — the agent’s closing summary, or the user’s message text. Empty string when there is no closing prose.

Ordered list of parts that make up the message. Iterate to render the full narrative including thinking, file operations, tool calls, and prose.

type: 'text'

A block of text output by the agent.

text: string

Markdown prose written by the agent or user.

startedAt?: string

ISO timestamp when this part began.

finishedAt?: string

ISO timestamp when this part completed.

Why generation ended. Null while the agent is still generating; once non-null, the message is final and safe to consume.

attachments?: object[]

Files attached to this message.

url: string

URL to the attachment.

name?: string

Original filename, when available.

contentType?: string

MIME type.

size?: integer

Size in bytes.

authorId: string | null

ID of the user who authored a user message; null for assistant messages.

usage: object

Token usage and credit cost. All values are zero on user messages and on assistant messages that have not yet generated tokens.

tokens: object

Token counts for this message.

input: number

Prompt input value (non-cached).

output: number

Completion output value.

cacheRead: number

Cache-read input value.

cacheWrite: number

Cache-write input value.

total: number

Sum of input, output, cacheRead, and cacheWrite.

creditsCost: object

Credit cost for this message.