streamText()

Streams text generations from a language model.

You can use the streamText function for interactive use cases such as chat bots and other real-time applications. You can also generate UI components with tools.

import { streamText } from 'ai';


const { textStream } = streamText({
  model: "anthropic/claude-sonnet-4.5",
  prompt: 'Invent a new holiday and describe its traditions.',
});


for await (const textPart of textStream) {
  process.stdout.write(textPart);
}

To see streamText in action, check out these examples.

Import 

import { streamText } from "ai"

API Signature

Parameters

model:

LanguageModel

system:

string

prompt:

string | Array<SystemModelMessage | UserModelMessage | AssistantModelMessage | ToolModelMessage>

messages:

Array<SystemModelMessage | UserModelMessage | AssistantModelMessage | ToolModelMessage>
SystemModelMessage

role:

'system'

content:

string
UserModelMessage

role:

'user'

content:

string | Array<TextPart | ImagePart | FilePart>
TextPart

type:

'text'

text:

string
ImagePart

type:

'image'

image:

string | Uint8Array | Buffer | ArrayBuffer | URL

mediaType?:

string
FilePart

type:

'file'

data:

string | Uint8Array | Buffer | ArrayBuffer | URL

mediaType:

string
AssistantModelMessage

role:

'assistant'

content:

string | Array<TextPart | FilePart | ReasoningPart | ToolCallPart>
TextPart

type:

'text'

text:

string
ReasoningPart

type:

'reasoning'

text:

string
FilePart

type:

'file'

data:

string | Uint8Array | Buffer | ArrayBuffer | URL

mediaType:

string

filename?:

string
ToolCallPart

type:

'tool-call'

toolCallId:

string

toolName:

string

input:

object based on zod schema
ToolModelMessage

role:

'tool'

content:

Array<ToolResultPart>
ToolResultPart

type:

'tool-result'

toolCallId:

string

toolName:

string

result:

unknown

isError?:

boolean

allowSystemInMessages?:

boolean

tools:

ToolSet
Tool

description?:

string

inputSchema:

Zod Schema | JSON Schema

execute?:

async (parameters: T, options: ToolExecutionOptions) => RESULT
ToolExecutionOptions

toolCallId:

string

messages:

ModelMessage[]

abortSignal:

AbortSignal

toolChoice?:

"auto" | "none" | "required" | { "type": "tool", "toolName": string }

maxOutputTokens?:

number

temperature?:

number

topP?:

number

topK?:

number

presencePenalty?:

number

frequencyPenalty?:

number

stopSequences?:

string[]

seed?:

number

maxRetries?:

number

abortSignal?:

AbortSignal

headers?:

Record<string, string>

experimental_generateMessageId?:

() => string

experimental_telemetry?:

TelemetrySettings
TelemetrySettings

isEnabled?:

boolean

recordInputs?:

boolean

recordOutputs?:

boolean

functionId?:

string

metadata?:

Record<string, string | number | boolean | Array<null | undefined | string> | Array<null | undefined | number> | Array<null | undefined | boolean>>

experimental_transform?:

StreamTextTransform | Array<StreamTextTransform>
StreamTextTransform

transform:

(options: TransformOptions) => TransformStream<TextStreamPart<TOOLS>, TextStreamPart<TOOLS>>
TransformOptions

stopStream:

() => void

tools:

TOOLS

includeRawChunks?:

boolean

providerOptions?:

Record<string,Record<string,JSONValue>> | undefined

activeTools?:

Array<TOOLNAME> | undefined

stopWhen?:

StopCondition<TOOLS> | Array<StopCondition<TOOLS>>

prepareStep?:

(options: PrepareStepOptions) => PrepareStepResult<TOOLS> | Promise<PrepareStepResult<TOOLS>>
PrepareStepFunction<TOOLS>

options:

object
PrepareStepOptions

steps:

Array<StepResult<TOOLS>>

stepNumber:

number

model:

LanguageModel

messages:

Array<ModelMessage>
PrepareStepResult<TOOLS>

model?:

LanguageModel

toolChoice?:

ToolChoice<TOOLS>

activeTools?:

Array<keyof TOOLS>

system?:

string

messages?:

Array<ModelMessage>

experimental_context?:

unknown

experimental_download?:

(requestedDownloads: Array<{ url: URL; isUrlSupportedByModel: boolean }>) => Promise<Array<null | { data: Uint8Array; mediaType?: string }>>

experimental_repairToolCall?:

(options: ToolCallRepairOptions) => Promise<LanguageModelV2ToolCall | null>
ToolCallRepairOptions

system:

string | undefined

messages:

ModelMessage[]

toolCall:

LanguageModelV2ToolCall

tools:

TOOLS

parameterSchema:

(options: { toolName: string }) => JSONSchema7

error:

NoSuchToolError | InvalidToolInputError

onChunk?:

(event: OnChunkResult) => Promise<void> |void
OnChunkResult

chunk:

TextStreamPart
TextStreamPart

type:

'text'

text:

string
TextStreamPart

type:

'reasoning'

text:

string
TextStreamPart

type:

'source'

source:

Source
TextStreamPart

type:

'tool-call'

toolCallId:

string

toolName:

string

input:

object based on zod schema
TextStreamPart

type:

'tool-call-streaming-start'

toolCallId:

string

toolName:

string
TextStreamPart

type:

'tool-call-delta'

toolCallId:

string

toolName:

string

argsTextDelta:

string
TextStreamPart

type:

'tool-result'

toolCallId:

string

toolName:

string

input:

object based on zod schema

output:

any

onError?:

(event: OnErrorResult) => Promise<void> |void
OnErrorResult

error:

unknown

experimental_output?:

Output
Output

Output.text():

Output

Output.object():

Output
Options

schema:

Schema<OBJECT>

onStepFinish?:

(result: onStepFinishResult) => Promise<void> | void
onStepFinishResult

stepType:

"initial" | "continue" | "tool-result"

finishReason:

"stop" | "length" | "content-filter" | "tool-calls" | "error" | "other" | "unknown"

usage:

LanguageModelUsage
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

text:

string

reasoning:

string | undefined

sources:

Array<Source>
Source

sourceType:

'url'

id:

string

url:

string

title?:

string

providerMetadata?:

SharedV2ProviderMetadata

files:

Array<GeneratedFile>
GeneratedFile

base64:

string

uint8Array:

Uint8Array

mediaType:

string

toolCalls:

ToolCall[]

toolResults:

ToolResult[]

warnings:

Warning[] | undefined

response?:

Response
Response

id:

string

model:

string

timestamp:

Date

headers?:

Record<string, string>

isContinued:

boolean

providerMetadata?:

Record<string,Record<string,JSONValue>> | undefined

onFinish?:

(result: OnFinishResult) => Promise<void> | void
OnFinishResult

finishReason:

"stop" | "length" | "content-filter" | "tool-calls" | "error" | "other" | "unknown"

usage:

LanguageModelUsage
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

providerMetadata:

Record<string,Record<string,JSONValue>> | undefined

text:

string

reasoningText:

string | undefined

reasoning:

Array<ReasoningDetail>
ReasoningDetail

type:

'text'

text:

string

signature?:

string
ReasoningDetail

type:

'redacted'

data:

string

sources:

Array<Source>
Source

sourceType:

'url'

id:

string

url:

string

title?:

string

providerMetadata?:

SharedV2ProviderMetadata

files:

Array<GeneratedFile>
GeneratedFile

base64:

string

uint8Array:

Uint8Array

mediaType:

string

toolCalls:

ToolCall[]

toolResults:

ToolResult[]

warnings:

Warning[] | undefined

response?:

Response
Response

id:

string

model:

string

timestamp:

Date

headers?:

Record<string, string>

messages:

Array<ResponseMessage>

steps:

Array<StepResult>

onAbort?:

(event: OnAbortResult) => Promise<void> | void
OnAbortResult

steps:

Array<StepResult>

Returns

content:

Promise<Array<ContentPart<TOOLS>>>

finishReason:

Promise<'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other' | 'unknown'>

usage:

Promise<LanguageModelUsage>
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

totalUsage:

Promise<LanguageModelUsage>
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

providerMetadata:

Promise<ProviderMetadata | undefined>

text:

Promise<string>

reasoning:

Promise<Array<ReasoningOutput>>
ReasoningOutput

type:

'reasoning'

text:

string

providerMetadata?:

SharedV2ProviderMetadata

reasoningText:

Promise<string | undefined>

sources:

Promise<Array<Source>>
Source

sourceType:

'url'

id:

string

url:

string

title?:

string

providerMetadata?:

SharedV2ProviderMetadata

files:

Promise<Array<GeneratedFile>>
GeneratedFile

base64:

string

uint8Array:

Uint8Array

mediaType:

string

toolCalls:

Promise<TypedToolCall<TOOLS>[]>

toolResults:

Promise<TypedToolResult<TOOLS>[]>

request:

Promise<LanguageModelRequestMetadata>
LanguageModelRequestMetadata

body:

string

response:

Promise<LanguageModelResponseMetadata & { messages: Array<ResponseMessage>; }>
LanguageModelResponseMetadata

id:

string

model:

string

timestamp:

Date

headers?:

Record<string, string>

messages:

Array<ResponseMessage>

warnings:

Promise<CallWarning[] | undefined>

steps:

Promise<Array<StepResult>>
StepResult

stepType:

"initial" | "continue" | "tool-result"

text:

string

reasoning:

string | undefined

sources:

Array<Source>
Source

sourceType:

'url'

id:

string

url:

string

title?:

string

providerMetadata?:

SharedV2ProviderMetadata

files:

Array<GeneratedFile>
GeneratedFile

base64:

string

uint8Array:

Uint8Array

mediaType:

string

toolCalls:

array

toolResults:

array

finishReason:

'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other' | 'unknown'

usage:

LanguageModelUsage
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

request?:

RequestMetadata
RequestMetadata

body:

string

response?:

ResponseMetadata
ResponseMetadata

id:

string

model:

string

timestamp:

Date

headers?:

Record<string, string>

messages:

Array<ResponseMessage>

warnings:

Warning[] | undefined

isContinued:

boolean

providerMetadata?:

Record<string,Record<string,JSONValue>> | undefined

textStream:

AsyncIterableStream<string>

fullStream:

AsyncIterable<TextStreamPart<TOOLS>> & ReadableStream<TextStreamPart<TOOLS>>
TextStreamPart

type:

'text'

text:

string
TextStreamPart

type:

'reasoning'

text:

string

providerMetadata?:

ProviderMetadata
TextStreamPart

type:

'source'

sourceType:

'url'

id:

string

url:

string

title?:

string

providerMetadata?:

ProviderMetadata
TextStreamPart

type:

'file'

file:

GeneratedFile
GeneratedFile

base64:

string

uint8Array:

Uint8Array

mediaType:

string
TextStreamPart

type:

'tool-call'

toolCallId:

string

toolName:

string

input:

object based on tool parameters
TextStreamPart

type:

'tool-call-streaming-start'

toolCallId:

string

toolName:

string
TextStreamPart

type:

'tool-call-delta'

toolCallId:

string

toolName:

string

argsTextDelta:

string
TextStreamPart

type:

'tool-result'

toolCallId:

string

toolName:

string

input:

object based on tool parameters

output:

tool execution return type
TextStreamPart

type:

'start-step'

request:

LanguageModelRequestMetadata
LanguageModelRequestMetadata

body:

string

warnings:

CallWarning[]
TextStreamPart

type:

'finish-step'

response:

LanguageModelResponseMetadata
LanguageModelResponseMetadata

id:

string

model:

string

timestamp:

Date

headers:

Record<string, string>

usage:

LanguageModelUsage
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined

finishReason:

'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other' | 'unknown'

providerMetadata?:

ProviderMetadata | undefined
TextStreamPart

type:

'start'
TextStreamPart

type:

'finish'

finishReason:

'stop' | 'length' | 'content-filter' | 'tool-calls' | 'error' | 'other' | 'unknown'

totalUsage:

LanguageModelUsage
LanguageModelUsage

inputTokens:

number | undefined

outputTokens:

number | undefined

totalTokens:

number | undefined

reasoningTokens?:

number | undefined

cachedInputTokens?:

number | undefined
TextStreamPart

type:

'reasoning-part-finish'
TextStreamPart

type:

'error'

error:

unknown
TextStreamPart

type:

'abort'

experimental_partialOutputStream:

AsyncIterableStream<PARTIAL_OUTPUT>

consumeStream:

(options?: ConsumeStreamOptions) => Promise<void>
ConsumeStreamOptions

onError?:

(error: unknown) => void

toUIMessageStream:

(options?: UIMessageStreamOptions) => AsyncIterableStream<UIMessageChunk>
UIMessageStreamOptions

originalMessages?:

UIMessage[]

onFinish?:

(options: { messages: UIMessage[]; isContinuation: boolean; responseMessage: UIMessage; isAborted: boolean; }) => void

messageMetadata?:

(options: { part: TextStreamPart<TOOLS> & { type: "start" | "finish" | "start-step" | "finish-step"; }; }) => unknown

sendReasoning?:

boolean

sendSources?:

boolean

sendFinish?:

boolean

sendStart?:

boolean

onError?:

(error: unknown) => string

consumeSseStream?:

(stream: ReadableStream) => Promise<void>

pipeUIMessageStreamToResponse:

(response: ServerResponse, options?: ResponseInit & UIMessageStreamOptions) => void
ResponseInit & UIMessageStreamOptions

status?:

number

statusText?:

string

headers?:

HeadersInit

pipeTextStreamToResponse:

(response: ServerResponse, init?: ResponseInit) => void
ResponseInit

status?:

number

statusText?:

string

headers?:

Record<string, string>

toUIMessageStreamResponse:

(options?: ResponseInit & UIMessageStreamOptions) => Response
ResponseInit & UIMessageStreamOptions

status?:

number

statusText?:

string

headers?:

HeadersInit

toTextStreamResponse:

(init?: ResponseInit) => Response
ResponseInit

status?:

number

statusText?:

string

headers?:

Record<string, string>

Examples

Learn to stream text generated by a language model in Next.js
Learn to stream chat completions generated by a language model in Next.js
Learn to stream text generated by a language model in Node.js
Learn to stream chat completions generated by a language model in Node.js