Create a Message

client.Messages.New(ctx, body) (*Message, error)

post/v1/messages

Send a structured list of input messages with text and/or image content, and the model will generate the next message in the conversation.

The Messages API can be used for either single queries or stateless multi-turn conversations.

Learn more about the Messages API in our user guide

ParametersExpand Collapse

body MessageNewParams

MaxTokens param.Field[int64]

The maximum number of tokens to generate before stopping.

Note that our models may stop before reaching this maximum. This parameter only specifies the absolute maximum number of tokens to generate.

Different models have different maximum values for this parameter. See models for details.

minimum1

Messages param.Field[[]MessageParamResp]

Input messages.

Our models are trained to operate on alternating user and assistant conversational turns. When creating a new Message, you specify the prior conversational turns with the messages parameter, and the model then generates the next Message in the conversation. Consecutive user or assistant turns in your request will be combined into a single turn.

Each input message must be an object with a role and content. You can specify a single user-role message, or you can include multiple user and assistant messages.

If the final message uses the assistant role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.

Example with a single user message:

[{"role": "user", "content": "Hello, Claude"}]

Example with multiple conversational turns:

[
  {"role": "user", "content": "Hello there."},
  {"role": "assistant", "content": "Hi, I'm Claude. How can I help you?"},
  {"role": "user", "content": "Can you explain LLMs in plain English?"},
]

Example with a partially-filled response from Claude:

[
  {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
  {"role": "assistant", "content": "The best answer is ("},
]

Each input message content may be either a single string or an array of content blocks, where each block has a specific type. Using a string for content is shorthand for an array of one content block of type "text". The following input messages are equivalent:

{"role": "user", "content": "Hello, Claude"}

{"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}

See input examples.

Note that if you want to include a system prompt, you can use the top-level system parameter — there is no "system" role for input messages in the Messages API.

There is a limit of 100,000 messages in a single request.

Content []ContentBlockParamUnionResp

Accepts one of the following:

[]ContentBlockParamUnionResp

Accepts one of the following:

type TextBlockParamResp struct{…}

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

type ImageBlockParamResp struct{…}

Source ImageBlockParamSourceUnionResp

Accepts one of the following:

type Base64ImageSource struct{…}

Data string

formatbyte

MediaType Base64ImageSourceMediaType

Accepts one of the following:

const Base64ImageSourceMediaTypeImageJPEG Base64ImageSourceMediaType = "image/jpeg"

const Base64ImageSourceMediaTypeImagePNG Base64ImageSourceMediaType = "image/png"

const Base64ImageSourceMediaTypeImageGIF Base64ImageSourceMediaType = "image/gif"

const Base64ImageSourceMediaTypeImageWebP Base64ImageSourceMediaType = "image/webp"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type URLImageSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Image

Accepts one of the following:

const ImageImage Image = "image"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type DocumentBlockParamResp struct{…}

Source DocumentBlockParamSourceUnionResp

Accepts one of the following:

type Base64PDFSource struct{…}

Data string

formatbyte

MediaType ApplicationPDF

Accepts one of the following:

const ApplicationPDFApplicationPDF ApplicationPDF = "application/pdf"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type PlainTextSource struct{…}

Data string

MediaType TextPlain

Accepts one of the following:

const TextPlainTextPlain TextPlain = "text/plain"

Type Text

Accepts one of the following:

const TextText Text = "text"

type ContentBlockSource struct{…}

Content ContentBlockSourceContentUnion

Accepts one of the following:

string

[]ContentBlockSourceContentItemUnion

Accepts one of the following:

type TextBlockParamResp struct{…}

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

type ImageBlockParamResp struct{…}

Source ImageBlockParamSourceUnionResp

Accepts one of the following:

type Base64ImageSource struct{…}

Data string

formatbyte

MediaType Base64ImageSourceMediaType

Accepts one of the following:

const Base64ImageSourceMediaTypeImageJPEG Base64ImageSourceMediaType = "image/jpeg"

const Base64ImageSourceMediaTypeImagePNG Base64ImageSourceMediaType = "image/png"

const Base64ImageSourceMediaTypeImageGIF Base64ImageSourceMediaType = "image/gif"

const Base64ImageSourceMediaTypeImageWebP Base64ImageSourceMediaType = "image/webp"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type URLImageSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Image

Accepts one of the following:

const ImageImage Image = "image"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Type Content

Accepts one of the following:

const ContentContent Content = "content"

type URLPDFSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Document

Accepts one of the following:

const DocumentDocument Document = "document"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations CitationsConfigParamRespoptional

Enabled booloptional

Context stringoptional

minLength1

Title stringoptional

maxLength500

minLength1

type SearchResultBlockParamResp struct{…}

Content []TextBlockParamResp

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

Source string

Title string

Type SearchResult

Accepts one of the following:

const SearchResultSearchResult SearchResult = "search_result"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations CitationsConfigParamRespoptional

Enabled booloptional

type ThinkingBlockParamResp struct{…}

Signature string

Thinking string

Type Thinking

Accepts one of the following:

const ThinkingThinking Thinking = "thinking"

type RedactedThinkingBlockParamResp struct{…}

Data string

Type RedactedThinking

Accepts one of the following:

const RedactedThinkingRedactedThinking RedactedThinking = "redacted_thinking"

type ToolUseBlockParamResp struct{…}

ID string

Input map[string, any]

Name string

maxLength200

minLength1

Type ToolUse

Accepts one of the following:

const ToolUseToolUse ToolUse = "tool_use"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type ToolResultBlockParamResp struct{…}

ToolUseID string

Type ToolResult

Accepts one of the following:

const ToolResultToolResult ToolResult = "tool_result"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Content []ToolResultBlockParamContentUnionRespoptional

Accepts one of the following:

[]ToolResultBlockParamContentUnionResp

Accepts one of the following:

type TextBlockParamResp struct{…}

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

type ImageBlockParamResp struct{…}

Source ImageBlockParamSourceUnionResp

Accepts one of the following:

type Base64ImageSource struct{…}

Data string

formatbyte

MediaType Base64ImageSourceMediaType

Accepts one of the following:

const Base64ImageSourceMediaTypeImageJPEG Base64ImageSourceMediaType = "image/jpeg"

const Base64ImageSourceMediaTypeImagePNG Base64ImageSourceMediaType = "image/png"

const Base64ImageSourceMediaTypeImageGIF Base64ImageSourceMediaType = "image/gif"

const Base64ImageSourceMediaTypeImageWebP Base64ImageSourceMediaType = "image/webp"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type URLImageSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Image

Accepts one of the following:

const ImageImage Image = "image"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type SearchResultBlockParamResp struct{…}

Content []TextBlockParamResp

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

Source string

Title string

Type SearchResult

Accepts one of the following:

const SearchResultSearchResult SearchResult = "search_result"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations CitationsConfigParamRespoptional

Enabled booloptional

type DocumentBlockParamResp struct{…}

Source DocumentBlockParamSourceUnionResp

Accepts one of the following:

type Base64PDFSource struct{…}

Data string

formatbyte

MediaType ApplicationPDF

Accepts one of the following:

const ApplicationPDFApplicationPDF ApplicationPDF = "application/pdf"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type PlainTextSource struct{…}

Data string

MediaType TextPlain

Accepts one of the following:

const TextPlainTextPlain TextPlain = "text/plain"

Type Text

Accepts one of the following:

const TextText Text = "text"

type ContentBlockSource struct{…}

Content ContentBlockSourceContentUnion

Accepts one of the following:

string

[]ContentBlockSourceContentItemUnion

Accepts one of the following:

type TextBlockParamResp struct{…}

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

type ImageBlockParamResp struct{…}

Source ImageBlockParamSourceUnionResp

Accepts one of the following:

type Base64ImageSource struct{…}

Data string

formatbyte

MediaType Base64ImageSourceMediaType

Accepts one of the following:

const Base64ImageSourceMediaTypeImageJPEG Base64ImageSourceMediaType = "image/jpeg"

const Base64ImageSourceMediaTypeImagePNG Base64ImageSourceMediaType = "image/png"

const Base64ImageSourceMediaTypeImageGIF Base64ImageSourceMediaType = "image/gif"

const Base64ImageSourceMediaTypeImageWebP Base64ImageSourceMediaType = "image/webp"

Type Base64

Accepts one of the following:

const Base64Base64 Base64 = "base64"

type URLImageSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Image

Accepts one of the following:

const ImageImage Image = "image"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Type Content

Accepts one of the following:

const ContentContent Content = "content"

type URLPDFSource struct{…}

Type URL

Accepts one of the following:

const URLURL URL = "url"

URL string

Type Document

Accepts one of the following:

const DocumentDocument Document = "document"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations CitationsConfigParamRespoptional

Enabled booloptional

Context stringoptional

minLength1

Title stringoptional

maxLength500

minLength1

IsError booloptional

type ServerToolUseBlockParamResp struct{…}

ID string

Input map[string, any]

Name WebSearch

Accepts one of the following:

const WebSearchWebSearch WebSearch = "web_search"

Type ServerToolUse

Accepts one of the following:

const ServerToolUseServerToolUse ServerToolUse = "server_tool_use"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type WebSearchToolResultBlockParamResp struct{…}

Content WebSearchToolResultBlockParamContentUnionResp

Accepts one of the following:

[]WebSearchResultBlockParamResp

EncryptedContent string

Title string

Type WebSearchResult

Accepts one of the following:

const WebSearchResultWebSearchResult WebSearchResult = "web_search_result"

URL string

PageAge stringoptional

type WebSearchToolRequestError struct{…}

ErrorCode WebSearchToolRequestErrorErrorCode

Accepts one of the following:

const WebSearchToolRequestErrorErrorCodeInvalidToolInput WebSearchToolRequestErrorErrorCode = "invalid_tool_input"

const WebSearchToolRequestErrorErrorCodeUnavailable WebSearchToolRequestErrorErrorCode = "unavailable"

const WebSearchToolRequestErrorErrorCodeMaxUsesExceeded WebSearchToolRequestErrorErrorCode = "max_uses_exceeded"

const WebSearchToolRequestErrorErrorCodeTooManyRequests WebSearchToolRequestErrorErrorCode = "too_many_requests"

const WebSearchToolRequestErrorErrorCodeQueryTooLong WebSearchToolRequestErrorErrorCode = "query_too_long"

Type WebSearchToolResultError

Accepts one of the following:

const WebSearchToolResultErrorWebSearchToolResultError WebSearchToolResultError = "web_search_tool_result_error"

ToolUseID string

Type WebSearchToolResult

Accepts one of the following:

const WebSearchToolResultWebSearchToolResult WebSearchToolResult = "web_search_tool_result"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Role MessageParamRole

Accepts one of the following:

const MessageParamRoleUser MessageParamRole = "user"

const MessageParamRoleAssistant MessageParamRole = "assistant"

Model param.Field[Model]

The model that will complete your prompt.

See models for additional details and options.

Metadata param.Field[Metadata]optional

An object describing metadata about the request.

ServiceTier param.Field[MessageNewParamsServiceTier]optional

Determines whether to use priority capacity (if available) or standard capacity for this request.

Anthropic offers different levels of service for your API requests. See service-tiers for details.

const MessageNewParamsServiceTierAuto MessageNewParamsServiceTier = "auto"

const MessageNewParamsServiceTierStandardOnly MessageNewParamsServiceTier = "standard_only"

StopSequences param.Field[[]string]optional

Custom text sequences that will cause the model to stop generating.

Our models will normally stop when they have naturally completed their turn, which will result in a response stop_reason of "end_turn".

If you want the model to stop generating when it encounters custom strings of text, you can use the stop_sequences parameter. If the model encounters one of the custom sequences, the response stop_reason value will be "stop_sequence" and the response stop_sequence value will contain the matched stop sequence.

System param.Field[[]TextBlockParamResp]optional

System prompt.

A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. See our guide to system prompts.

[]TextBlockParam

Text string

minLength1

Type Text

Accepts one of the following:

const TextText Text = "text"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Citations []TextCitationParamUnionRespoptional

Accepts one of the following:

type CitationCharLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndCharIndex int64

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndPageNumber int64

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocationParamResp struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

maxLength255

minLength1

EndBlockIndex int64

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationWebSearchResultLocationParamResp struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

minLength1

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

maxLength2048

minLength1

type CitationSearchResultLocationParamResp struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

Temperature param.Field[float64]optional

Amount of randomness injected into the response.

Defaults to 1.0. Ranges from 0.0 to 1.0. Use temperature closer to 0.0 for analytical / multiple choice, and closer to 1.0 for creative and generative tasks.

Note that even with temperature of 0.0, the results will not be fully deterministic.

maximum1

minimum0

Thinking param.Field[ThinkingConfigParamUnionResp]optional

Configuration for enabling Claude's extended thinking.

When enabled, responses include thinking content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your max_tokens limit.

See extended thinking for details.

ToolChoice param.Field[ToolChoiceUnion]optional

How the model should use the provided tools. The model can use a specific tool, any available tool, decide by itself, or not use tools at all.

Tools param.Field[[]ToolUnion]optional

Definitions of tools that the model may use.

If you include tools in your API request, the model may return tool_use content blocks that represent the model's use of those tools. You can then run those tools using the tool input generated by the model and then optionally return results back to the model using tool_result content blocks.

There are two types of tools: client tools and server tools. The behavior described below applies to client tools. For server tools, see their individual documentation as each has its own behavior (e.g., the web search tool).

Each tool definition includes:

name: Name of the tool.
description: Optional, but strongly-recommended description of the tool.
input_schema: JSON schema for the tool input shape that the model will produce in tool_use output content blocks.

For example, if you defined tools as:

[
  {
    "name": "get_stock_price",
    "description": "Get the current stock price for a given ticker symbol.",
    "input_schema": {
      "type": "object",
      "properties": {
        "ticker": {
          "type": "string",
          "description": "The stock ticker symbol, e.g. AAPL for Apple Inc."
        }
      },
      "required": ["ticker"]
    }
  }
]

And then asked the model "What's the S&P 500 at today?", the model might produce tool_use content blocks in the response like this:

[
  {
    "type": "tool_use",
    "id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
    "name": "get_stock_price",
    "input": { "ticker": "^GSPC" }
  }
]

You might then run your get_stock_price tool with {"ticker": "^GSPC"} as an input, and return the following back to the model in a subsequent user message:

[
  {
    "type": "tool_result",
    "tool_use_id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
    "content": "259.75 USD"
  }
]

Tools can be used for workflows that include running client-side tools and functions, or more generally whenever you want the model to produce a particular JSON structure of output.

See our guide for more details.

type Tool struct{…}

InputSchema ToolInputSchema

JSON schema for this tool's input.

This defines the shape of the input that your tool accepts and that the model will produce.

Type Object

Accepts one of the following:

const ObjectObject Object = "object"

Properties map[string, any]optional

Required []stringoptional

Name string

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

maxLength128

minLength1

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

Description stringoptional

Description of what this tool does.

Tool descriptions should be as detailed as possible. The more information that the model has about what the tool is and how to use it, the better it will perform. You can use natural language descriptions to reinforce important aspects of the tool input JSON schema.

Type ToolTypeoptional

Accepts one of the following:

const ToolTypeCustom ToolType = "custom"

type ToolBash20250124 struct{…}

Name Bash

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

Accepts one of the following:

const BashBash Bash = "bash"

Type Bash20250124

Accepts one of the following:

const Bash20250124Bash20250124 Bash20250124 = "bash_20250124"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type ToolTextEditor20250124 struct{…}

Name StrReplaceEditor

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

Accepts one of the following:

const StrReplaceEditorStrReplaceEditor StrReplaceEditor = "str_replace_editor"

Type TextEditor20250124

Accepts one of the following:

const TextEditor20250124TextEditor20250124 TextEditor20250124 = "text_editor_20250124"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type ToolTextEditor20250429 struct{…}

Name StrReplaceBasedEditTool

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

Accepts one of the following:

const StrReplaceBasedEditToolStrReplaceBasedEditTool StrReplaceBasedEditTool = "str_replace_based_edit_tool"

Type TextEditor20250429

Accepts one of the following:

const TextEditor20250429TextEditor20250429 TextEditor20250429 = "text_editor_20250429"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

type ToolTextEditor20250728 struct{…}

Name StrReplaceBasedEditTool

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

Accepts one of the following:

const StrReplaceBasedEditToolStrReplaceBasedEditTool StrReplaceBasedEditTool = "str_replace_based_edit_tool"

Type TextEditor20250728

Accepts one of the following:

const TextEditor20250728TextEditor20250728 TextEditor20250728 = "text_editor_20250728"

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

MaxCharacters int64optional

Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.

minimum1

type WebSearchTool20250305 struct{…}

Name WebSearch

Name of the tool.

This is how the tool will be called by the model and in tool_use blocks.

Accepts one of the following:

const WebSearchWebSearch WebSearch = "web_search"

Type WebSearch20250305

Accepts one of the following:

const WebSearch20250305WebSearch20250305 WebSearch20250305 = "web_search_20250305"

AllowedDomains []stringoptional

If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

BlockedDomains []stringoptional

If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

CacheControl CacheControlEphemeraloptional

Create a cache control breakpoint at this content block.

Type Ephemeral

Accepts one of the following:

const EphemeralEphemeral Ephemeral = "ephemeral"

TTL CacheControlEphemeralTTLoptional

The time-to-live for the cache control breakpoint.

This may be one the following values:

5m: 5 minutes
1h: 1 hour

Defaults to 5m.

Accepts one of the following:

const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"

const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"

MaxUses int64optional

Maximum number of times the tool can be used in the API request.

exclusiveMinimum0

UserLocation WebSearchTool20250305UserLocationoptional

Parameters for the user's location. Used to provide more relevant search results.

Type Approximate

Accepts one of the following:

const ApproximateApproximate Approximate = "approximate"

City stringoptional

The city of the user.

maxLength255

minLength1

Country stringoptional

The two letter ISO country code of the user.

maxLength2

minLength2

Region stringoptional

The region of the user.

maxLength255

minLength1

Timezone stringoptional

The IANA timezone of the user.

maxLength255

minLength1

TopK param.Field[int64]optional

Only sample from the top K options for each subsequent token.

Used to remove "long tail" low probability responses. Learn more technical details here.

Recommended for advanced use cases only. You usually only need to use temperature.

minimum0

TopP param.Field[float64]optional

Use nucleus sampling.

In nucleus sampling, we compute the cumulative distribution over all the options for each subsequent token in decreasing probability order and cut it off once it reaches a particular probability specified by top_p. You should either alter temperature or top_p, but not both.

Recommended for advanced use cases only. You usually only need to use temperature.

maximum1

minimum0

ReturnsExpand Collapse

type Message struct{…}

ID string

Unique object identifier.

The format and length of IDs may change over time.

Content []ContentBlockUnion

Content generated by the model.

This is an array of content blocks, each of which has a type that determines its shape.

Example:

[{"type": "text", "text": "Hi, I'm Claude."}]

If the request input messages ended with an assistant turn, then the response content will continue directly from that last turn. You can use this to constrain the model's output.

For example, if the input messages were:

[
  {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
  {"role": "assistant", "content": "The best answer is ("}
]

Then the response content might be:

[{"type": "text", "text": "B)"}]

Accepts one of the following:

type TextBlock struct{…}

Citations []TextCitationUnion

Citations supporting the text block.

The type of citation returned will depend on the type of document being cited. Citing a PDF results in page_location, plain text results in char_location, and content document results in content_block_location.

Accepts one of the following:

type CitationCharLocation struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

EndCharIndex int64

FileID string

StartCharIndex int64

minimum0

Type CharLocation

Accepts one of the following:

const CharLocationCharLocation CharLocation = "char_location"

type CitationPageLocation struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

EndPageNumber int64

FileID string

StartPageNumber int64

minimum1

Type PageLocation

Accepts one of the following:

const PageLocationPageLocation PageLocation = "page_location"

type CitationContentBlockLocation struct{…}

CitedText string

DocumentIndex int64

minimum0

DocumentTitle string

EndBlockIndex int64

FileID string

StartBlockIndex int64

minimum0

Type ContentBlockLocation

Accepts one of the following:

const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"

type CitationsWebSearchResultLocation struct{…}

CitedText string

EncryptedIndex string

Title string

maxLength512

Type WebSearchResultLocation

Accepts one of the following:

const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"

URL string

type CitationsSearchResultLocation struct{…}

CitedText string

EndBlockIndex int64

SearchResultIndex int64

minimum0

Source string

StartBlockIndex int64

minimum0

Title string

Type SearchResultLocation

Accepts one of the following:

const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"

Text string

maxLength5000000

minLength0

Type Text

Accepts one of the following:

const TextText Text = "text"

type ThinkingBlock struct{…}

Signature string

Thinking string

Type Thinking

Accepts one of the following:

const ThinkingThinking Thinking = "thinking"

type RedactedThinkingBlock struct{…}

Data string

Type RedactedThinking

Accepts one of the following:

const RedactedThinkingRedactedThinking RedactedThinking = "redacted_thinking"

type ToolUseBlock struct{…}

ID string

Input map[string, any]

Name string

minLength1

Type ToolUse

Accepts one of the following:

const ToolUseToolUse ToolUse = "tool_use"

type ServerToolUseBlock struct{…}

ID string

Input map[string, any]

Name WebSearch

Accepts one of the following:

const WebSearchWebSearch WebSearch = "web_search"

Type ServerToolUse

Accepts one of the following:

const ServerToolUseServerToolUse ServerToolUse = "server_tool_use"

type WebSearchToolResultBlock struct{…}

Content WebSearchToolResultBlockContentUnion

Accepts one of the following:

type WebSearchToolResultError struct{…}

ErrorCode WebSearchToolResultErrorErrorCode

Accepts one of the following:

const WebSearchToolResultErrorErrorCodeInvalidToolInput WebSearchToolResultErrorErrorCode = "invalid_tool_input"

const WebSearchToolResultErrorErrorCodeUnavailable WebSearchToolResultErrorErrorCode = "unavailable"

const WebSearchToolResultErrorErrorCodeMaxUsesExceeded WebSearchToolResultErrorErrorCode = "max_uses_exceeded"

const WebSearchToolResultErrorErrorCodeTooManyRequests WebSearchToolResultErrorErrorCode = "too_many_requests"

const WebSearchToolResultErrorErrorCodeQueryTooLong WebSearchToolResultErrorErrorCode = "query_too_long"

Type WebSearchToolResultError

Accepts one of the following:

const WebSearchToolResultErrorWebSearchToolResultError WebSearchToolResultError = "web_search_tool_result_error"

type WebSearchToolResultBlockContentArray []WebSearchResultBlock

EncryptedContent string

PageAge string

Title string

Type WebSearchResult

Accepts one of the following:

const WebSearchResultWebSearchResult WebSearchResult = "web_search_result"

URL string

ToolUseID string

Type WebSearchToolResult

Accepts one of the following:

const WebSearchToolResultWebSearchToolResult WebSearchToolResult = "web_search_tool_result"

Model Model

The model that will complete your prompt.

See models for additional details and options.

Accepts one of the following:

type Model string

The model that will complete your prompt.

See models for additional details and options.

Accepts one of the following:

const ModelClaude3_7SonnetLatest Model = "claude-3-7-sonnet-latest"

High-performance model with early extended thinking

const ModelClaude3_7Sonnet20250219 Model = "claude-3-7-sonnet-20250219"

High-performance model with early extended thinking

const ModelClaude3_5HaikuLatest Model = "claude-3-5-haiku-latest"

Fastest and most compact model for near-instant responsiveness

const ModelClaude3_5Haiku20241022 Model = "claude-3-5-haiku-20241022"

Our fastest model

const ModelClaudeHaiku4_5 Model = "claude-haiku-4-5"

Hybrid model, capable of near-instant responses and extended thinking

const ModelClaudeHaiku4_5_20251001 Model = "claude-haiku-4-5-20251001"

Hybrid model, capable of near-instant responses and extended thinking

const ModelClaudeSonnet4_20250514 Model = "claude-sonnet-4-20250514"

High-performance model with extended thinking

const ModelClaudeSonnet4_0 Model = "claude-sonnet-4-0"

High-performance model with extended thinking

const ModelClaude4Sonnet20250514 Model = "claude-4-sonnet-20250514"

High-performance model with extended thinking

const ModelClaudeSonnet4_5 Model = "claude-sonnet-4-5"

Our best model for real-world agents and coding

const ModelClaudeSonnet4_5_20250929 Model = "claude-sonnet-4-5-20250929"

Our best model for real-world agents and coding

const ModelClaudeOpus4_0 Model = "claude-opus-4-0"

Our most capable model

const ModelClaudeOpus4_20250514 Model = "claude-opus-4-20250514"

Our most capable model

const ModelClaude4Opus20250514 Model = "claude-4-opus-20250514"

Our most capable model

const ModelClaudeOpus4_1_20250805 Model = "claude-opus-4-1-20250805"

Our most capable model

const ModelClaude3OpusLatest Model = "claude-3-opus-latest"

Excels at writing and complex tasks

const ModelClaude_3_Opus_20240229 Model = "claude-3-opus-20240229"

Excels at writing and complex tasks

const ModelClaude_3_Haiku_20240307 Model = "claude-3-haiku-20240307"

Our previous most fast and cost-effective

string

Role Assistant

Conversational role of the generated message.

This will always be "assistant".

Accepts one of the following:

const AssistantAssistant Assistant = "assistant"

StopReason StopReason

The reason that we stopped.

This may be one the following values:

"end_turn": the model reached a natural stopping point
"max_tokens": we exceeded the requested max_tokens or the model's maximum
"stop_sequence": one of your provided custom stop_sequences was generated
"tool_use": the model invoked one or more tools
"pause_turn": we paused a long-running turn. You may provide the response back as-is in a subsequent request to let the model continue.
"refusal": when streaming classifiers intervene to handle potential policy violations

In non-streaming mode this value is always non-null. In streaming mode, it is null in the message_start event and non-null otherwise.

Accepts one of the following:

const StopReasonEndTurn StopReason = "end_turn"

const StopReasonMaxTokens StopReason = "max_tokens"

const StopReasonStopSequence StopReason = "stop_sequence"

const StopReasonToolUse StopReason = "tool_use"

const StopReasonPauseTurn StopReason = "pause_turn"

const StopReasonRefusal StopReason = "refusal"

StopSequence string

Which custom stop sequence was generated, if any.

This value will be a non-null string if one of your custom stop sequences was generated.

Type Message

Object type.

For Messages, this is always "message".

Accepts one of the following:

const MessageMessage Message = "message"

Usage Usage

Billing and rate-limit usage.

Anthropic's API bills and rate-limits by token counts, as tokens represent the underlying cost to our systems.

Under the hood, the API transforms requests into a format suitable for the model. The model's output then goes through a parsing stage before becoming an API response. As a result, the token counts in usage will not match one-to-one with the exact visible content of an API request or response.

For example, output_tokens will be non-zero, even for an empty string response from Claude.

Total input tokens in a request is the summation of input_tokens, cache_creation_input_tokens, and cache_read_input_tokens.

CacheCreation CacheCreation

Breakdown of cached tokens by TTL

Ephemeral1hInputTokens int64

The number of input tokens used to create the 1 hour cache entry.

minimum0

Ephemeral5mInputTokens int64

The number of input tokens used to create the 5 minute cache entry.

minimum0

CacheCreationInputTokens int64

The number of input tokens used to create the cache entry.

minimum0

CacheReadInputTokens int64

The number of input tokens read from the cache.

minimum0

InputTokens int64

The number of input tokens which were used.

minimum0

OutputTokens int64

The number of output tokens which were used.

minimum0

ServerToolUse ServerToolUsage

The number of server tool requests.

WebSearchRequests int64

The number of web search tool requests.

minimum0

ServiceTier UsageServiceTier

If the request used the priority, standard, or batch tier.

Accepts one of the following:

const UsageServiceTierStandard UsageServiceTier = "standard"

const UsageServiceTierPriority UsageServiceTier = "priority"

const UsageServiceTierBatch UsageServiceTier = "batch"

Create a Message

package main

import (
  "context"
  "fmt"

  "github.com/anthropics/anthropic-sdk-go"
  "github.com/anthropics/anthropic-sdk-go/option"
)

func main() {
  client := anthropic.NewClient(
    option.WithAPIKey("my-anthropic-api-key"),
  )
  message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
    MaxTokens: 1024,
    Messages: []anthropic.MessageParam{anthropic.MessageParam{
      Content: []anthropic.ContentBlockParamUnion{anthropic.ContentBlockParamUnion{
        OfText: &anthropic.TextBlockParam{Text: "What is a quaternion?", CacheControl: anthropic.CacheControlEphemeralParam{TTL: anthropic.CacheControlEphemeralTTLTTL5m}, Citations: []anthropic.TextCitationParamUnion{anthropic.TextCitationParamUnion{
          OfCharLocation: &anthropic.CitationCharLocationParam{CitedText: "cited_text", DocumentIndex: 0, DocumentTitle: anthropic.String("x"), EndCharIndex: 0, StartCharIndex: 0},
        }}},
      }},
      Role: anthropic.MessageParamRoleUser,
    }},
    Model: anthropic.ModelClaude3_7SonnetLatest,
  })
  if err != nil {
    panic(err.Error())
  }
  fmt.Printf("%+v\n", message.ID)
}

{
  "id": "msg_013Zva2CMHLNnXjNJJKqJ2EF",
  "content": [
    {
      "citations": [
        {
          "cited_text": "cited_text",
          "document_index": 0,
          "document_title": "document_title",
          "end_char_index": 0,
          "file_id": "file_id",
          "start_char_index": 0,
          "type": "char_location"
        }
      ],
      "text": "Hi! My name is Claude.",
      "type": "text"
    }
  ],
  "model": "claude-sonnet-4-5-20250929",
  "role": "assistant",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "cache_creation": {
      "ephemeral_1h_input_tokens": 0,
      "ephemeral_5m_input_tokens": 0
    },
    "cache_creation_input_tokens": 2051,
    "cache_read_input_tokens": 2051,
    "input_tokens": 2095,
    "output_tokens": 503,
    "server_tool_use": {
      "web_search_requests": 0
    },
    "service_tier": "standard"
  }
}

Returns Examples

{
  "id": "msg_013Zva2CMHLNnXjNJJKqJ2EF",
  "content": [
    {
      "citations": [
        {
          "cited_text": "cited_text",
          "document_index": 0,
          "document_title": "document_title",
          "end_char_index": 0,
          "file_id": "file_id",
          "start_char_index": 0,
          "type": "char_location"
        }
      ],
      "text": "Hi! My name is Claude.",
      "type": "text"
    }
  ],
  "model": "claude-sonnet-4-5-20250929",
  "role": "assistant",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "cache_creation": {
      "ephemeral_1h_input_tokens": 0,
      "ephemeral_5m_input_tokens": 0
    },
    "cache_creation_input_tokens": 2051,
    "cache_read_input_tokens": 2051,
    "input_tokens": 2095,
    "output_tokens": 503,
    "server_tool_use": {
      "web_search_requests": 0
    },
    "service_tier": "standard"
  }
}

Create a Message

ParametersExpand Collapse

ReturnsExpand Collapse

Create a Message

Returns Examples

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