Getting started

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Create

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Parameters

• MessageCreateParams = MessageCreateParamsNonStreaming | MessageCreateParamsStreaming
  • MessageCreateParamsBase
    • max_tokens: number 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.
    • messages: Array<MessageParam> 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: string | Array<ContentBlockParam>
        • string
        • Array<ContentBlockParam>
          • TextBlockParam
            • text: string
            • type: "text"
              • "text"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
            • citations?: Array<TextCitationParam> | null
              • CitationCharLocationParam
                • cited_text: string
                • document_index: number
                • document_title: string | null
                • end_char_index: number
                • start_char_index: number
                • type: "char_location"
                  • "char_location"
              • CitationPageLocationParam
                • cited_text: string
                • document_index: number
                • document_title: string | null
                • end_page_number: number
                • start_page_number: number
                • type: "page_location"
                  • "page_location"
              • CitationContentBlockLocationParam
                • cited_text: string
                • document_index: number
                • document_title: string | null
                • end_block_index: number
                • start_block_index: number
                • type: "content_block_location"
                  • "content_block_location"
              • CitationWebSearchResultLocationParam
                • cited_text: string
                • encrypted_index: string
                • title: string | null
                • type: "web_search_result_location"
                  • "web_search_result_location"
                • url: string
              • CitationSearchResultLocationParam
                • cited_text: string
                • end_block_index: number
                • search_result_index: number
                • source: string
                • start_block_index: number
                • title: string | null
                • type: "search_result_location"
                  • "search_result_location"
          • ImageBlockParam
            • source: Base64ImageSource | URLImageSource
              • Base64ImageSource
                • data: string
                • media_type: "image/jpeg" | "image/png" | "image/gif" | "image/webp"
                  • "image/jpeg"
                  • "image/png"
                  • "image/gif"
                  • "image/webp"
                • type: "base64"
                  • "base64"
              • URLImageSource
                • type: "url"
                  • "url"
                • url: string
            • type: "image"
              • "image"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
          • DocumentBlockParam
            • source: Base64PDFSource | PlainTextSource | ContentBlockSource | URLPDFSource
              • Base64PDFSource
                • data: string
                • media_type: "application/pdf"
                  • "application/pdf"
                • type: "base64"
                  • "base64"
              • PlainTextSource
                • data: string
                • media_type: "text/plain"
                  • "text/plain"
                • type: "text"
                  • "text"
              • ContentBlockSource
                • content: string | Array<ContentBlockSourceContent>
                  • string
                  • Array<ContentBlockSourceContent>
                    • TextBlockParam
                      • text: string
                      • type: "text"
                        • "text"
                      • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                        • type: "ephemeral"
                          • "ephemeral"
                        • ttl?: "5m" | "1h" 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.
                          • "5m"
                          • "1h"
                      • citations?: Array<TextCitationParam> | null
                        • CitationCharLocationParam
                          • cited_text: string
                          • document_index: number
                          • document_title: string | null
                          • end_char_index: number
                          • start_char_index: number
                          • type: "char_location"
                            • "char_location"
                        • CitationPageLocationParam
                          • cited_text: string
                          • document_index: number
                          • document_title: string | null
                          • end_page_number: number
                          • start_page_number: number
                          • type: "page_location"
                            • "page_location"
                        • CitationContentBlockLocationParam
                          • cited_text: string
                          • document_index: number
                          • document_title: string | null
                          • end_block_index: number
                          • start_block_index: number
                          • type: "content_block_location"
                            • "content_block_location"
                        • CitationWebSearchResultLocationParam
                          • cited_text: string
                          • encrypted_index: string
                          • title: string | null
                          • type: "web_search_result_location"
                            • "web_search_result_location"
                          • url: string
                        • CitationSearchResultLocationParam
                          • cited_text: string
                          • end_block_index: number
                          • search_result_index: number
                          • source: string
                          • start_block_index: number
                          • title: string | null
                          • type: "search_result_location"
                            • "search_result_location"
                    • ImageBlockParam
                      • source: Base64ImageSource | URLImageSource
                        • Base64ImageSource
                          • data: string
                          • media_type: "image/jpeg" | "image/png" | "image/gif" | "image/webp"
                            • "image/jpeg"
                            • "image/png"
                            • "image/gif"
                            • "image/webp"
                          • type: "base64"
                            • "base64"
                        • URLImageSource
                          • type: "url"
                            • "url"
                          • url: string
                      • type: "image"
                        • "image"
                      • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                        • type: "ephemeral"
                          • "ephemeral"
                        • ttl?: "5m" | "1h" 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.
                          • "5m"
                          • "1h"
                • type: "content"
                  • "content"
              • URLPDFSource
                • type: "url"
                  • "url"
                • url: string
            • type: "document"
              • "document"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
            • citations?: CitationsConfigParam | null
              • enabled?: boolean
            • context?: string | null
            • title?: string | null
          • SearchResultBlockParam
            • content: Array<TextBlockParam>
              • text: string
              • type: "text"
                • "text"
              • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                • type: "ephemeral"
                  • "ephemeral"
                • ttl?: "5m" | "1h" 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.
                  • "5m"
                  • "1h"
              • citations?: Array<TextCitationParam> | null
                • CitationCharLocationParam
                  • cited_text: string
                  • document_index: number
                  • document_title: string | null
                  • end_char_index: number
                  • start_char_index: number
                  • type: "char_location"
                    • "char_location"
                • CitationPageLocationParam
                  • cited_text: string
                  • document_index: number
                  • document_title: string | null
                  • end_page_number: number
                  • start_page_number: number
                  • type: "page_location"
                    • "page_location"
                • CitationContentBlockLocationParam
                  • cited_text: string
                  • document_index: number
                  • document_title: string | null
                  • end_block_index: number
                  • start_block_index: number
                  • type: "content_block_location"
                    • "content_block_location"
                • CitationWebSearchResultLocationParam
                  • cited_text: string
                  • encrypted_index: string
                  • title: string | null
                  • type: "web_search_result_location"
                    • "web_search_result_location"
                  • url: string
                • CitationSearchResultLocationParam
                  • cited_text: string
                  • end_block_index: number
                  • search_result_index: number
                  • source: string
                  • start_block_index: number
                  • title: string | null
                  • type: "search_result_location"
                    • "search_result_location"
            • source: string
            • title: string
            • type: "search_result"
              • "search_result"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
            • citations?: CitationsConfigParam
              • enabled?: boolean
          • ThinkingBlockParam
            • signature: string
            • thinking: string
            • type: "thinking"
              • "thinking"
          • RedactedThinkingBlockParam
            • data: string
            • type: "redacted_thinking"
              • "redacted_thinking"
          • ToolUseBlockParam
            • id: string
            • input: Record<string, unknown>
            • name: string
            • type: "tool_use"
              • "tool_use"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
          • ToolResultBlockParam
            • tool_use_id: string
            • type: "tool_result"
              • "tool_result"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
            • content?: string | Array<TextBlockParam | ImageBlockParam | SearchResultBlockParam | DocumentBlockParam>
              • string
              • Array<TextBlockParam | ImageBlockParam | SearchResultBlockParam | DocumentBlockParam>
                • TextBlockParam
                  • text: string
                  • type: "text"
                    • "text"
                  • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                    • type: "ephemeral"
                      • "ephemeral"
                    • ttl?: "5m" | "1h" 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.
                      • "5m"
                      • "1h"
                  • citations?: Array<TextCitationParam> | null
                    • CitationCharLocationParam
                      • cited_text: string
                      • document_index: number
                      • document_title: string | null
                      • end_char_index: number
                      • start_char_index: number
                      • type: "char_location"
                        • "char_location"
                    • CitationPageLocationParam
                      • cited_text: string
                      • document_index: number
                      • document_title: string | null
                      • end_page_number: number
                      • start_page_number: number
                      • type: "page_location"
                        • "page_location"
                    • CitationContentBlockLocationParam
                      • cited_text: string
                      • document_index: number
                      • document_title: string | null
                      • end_block_index: number
                      • start_block_index: number
                      • type: "content_block_location"
                        • "content_block_location"
                    • CitationWebSearchResultLocationParam
                      • cited_text: string
                      • encrypted_index: string
                      • title: string | null
                      • type: "web_search_result_location"
                        • "web_search_result_location"
                      • url: string
                    • CitationSearchResultLocationParam
                      • cited_text: string
                      • end_block_index: number
                      • search_result_index: number
                      • source: string
                      • start_block_index: number
                      • title: string | null
                      • type: "search_result_location"
                        • "search_result_location"
                • ImageBlockParam
                  • source: Base64ImageSource | URLImageSource
                    • Base64ImageSource
                      • data: string
                      • media_type: "image/jpeg" | "image/png" | "image/gif" | "image/webp"
                        • "image/jpeg"
                        • "image/png"
                        • "image/gif"
                        • "image/webp"
                      • type: "base64"
                        • "base64"
                    • URLImageSource
                      • type: "url"
                        • "url"
                      • url: string
                  • type: "image"
                    • "image"
                  • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                    • type: "ephemeral"
                      • "ephemeral"
                    • ttl?: "5m" | "1h" 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.
                      • "5m"
                      • "1h"
                • SearchResultBlockParam
                  • content: Array<TextBlockParam>
                    • text: string
                    • type: "text"
                      • "text"
                    • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                      • type: "ephemeral"
                        • "ephemeral"
                      • ttl?: "5m" | "1h" 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.
                        • "5m"
                        • "1h"
                    • citations?: Array<TextCitationParam> | null
                      • CitationCharLocationParam
                        • cited_text: string
                        • document_index: number
                        • document_title: string | null
                        • end_char_index: number
                        • start_char_index: number
                        • type: "char_location"
                          • "char_location"
                      • CitationPageLocationParam
                        • cited_text: string
                        • document_index: number
                        • document_title: string | null
                        • end_page_number: number
                        • start_page_number: number
                        • type: "page_location"
                          • "page_location"
                      • CitationContentBlockLocationParam
                        • cited_text: string
                        • document_index: number
                        • document_title: string | null
                        • end_block_index: number
                        • start_block_index: number
                        • type: "content_block_location"
                          • "content_block_location"
                      • CitationWebSearchResultLocationParam
                        • cited_text: string
                        • encrypted_index: string
                        • title: string | null
                        • type: "web_search_result_location"
                          • "web_search_result_location"
                        • url: string
                      • CitationSearchResultLocationParam
                        • cited_text: string
                        • end_block_index: number
                        • search_result_index: number
                        • source: string
                        • start_block_index: number
                        • title: string | null
                        • type: "search_result_location"
                          • "search_result_location"
                  • source: string
                  • title: string
                  • type: "search_result"
                    • "search_result"
                  • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                    • type: "ephemeral"
                      • "ephemeral"
                    • ttl?: "5m" | "1h" 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.
                      • "5m"
                      • "1h"
                  • citations?: CitationsConfigParam
                    • enabled?: boolean
                • DocumentBlockParam
                  • source: Base64PDFSource | PlainTextSource | ContentBlockSource | URLPDFSource
                    • Base64PDFSource
                      • data: string
                      • media_type: "application/pdf"
                        • "application/pdf"
                      • type: "base64"
                        • "base64"
                    • PlainTextSource
                      • data: string
                      • media_type: "text/plain"
                        • "text/plain"
                      • type: "text"
                        • "text"
                    • ContentBlockSource
                      • content: string | Array<ContentBlockSourceContent>
                        • string
                        • Array<ContentBlockSourceContent>
                          • TextBlockParam
                            • text: string
                            • type: "text"
                              • "text"
                            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                              • type: "ephemeral"
                                • "ephemeral"
                              • ttl?: "5m" | "1h" 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.
                                • "5m"
                                • "1h"
                            • citations?: Array<TextCitationParam> | null
                              • CitationCharLocationParam
                                • cited_text: string
                                • document_index: number
                                • document_title: string | null
                                • end_char_index: number
                                • start_char_index: number
                                • type: "char_location"
                                  • "char_location"
                              • CitationPageLocationParam
                                • cited_text: string
                                • document_index: number
                                • document_title: string | null
                                • end_page_number: number
                                • start_page_number: number
                                • type: "page_location"
                                  • "page_location"
                              • CitationContentBlockLocationParam
                                • cited_text: string
                                • document_index: number
                                • document_title: string | null
                                • end_block_index: number
                                • start_block_index: number
                                • type: "content_block_location"
                                  • "content_block_location"
                              • CitationWebSearchResultLocationParam
                                • cited_text: string
                                • encrypted_index: string
                                • title: string | null
                                • type: "web_search_result_location"
                                  • "web_search_result_location"
                                • url: string
                              • CitationSearchResultLocationParam
                                • cited_text: string
                                • end_block_index: number
                                • search_result_index: number
                                • source: string
                                • start_block_index: number
                                • title: string | null
                                • type: "search_result_location"
                                  • "search_result_location"
                          • ImageBlockParam
                            • source: Base64ImageSource | URLImageSource
                              • Base64ImageSource
                                • data: string
                                • media_type: "image/jpeg" | "image/png" | "image/gif" | "image/webp"
                                  • "image/jpeg"
                                  • "image/png"
                                  • "image/gif"
                                  • "image/webp"
                                • type: "base64"
                                  • "base64"
                              • URLImageSource
                                • type: "url"
                                  • "url"
                                • url: string
                            • type: "image"
                              • "image"
                            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                              • type: "ephemeral"
                                • "ephemeral"
                              • ttl?: "5m" | "1h" 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.
                                • "5m"
                                • "1h"
                      • type: "content"
                        • "content"
                    • URLPDFSource
                      • type: "url"
                        • "url"
                      • url: string
                  • type: "document"
                    • "document"
                  • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
                    • type: "ephemeral"
                      • "ephemeral"
                    • ttl?: "5m" | "1h" 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.
                      • "5m"
                      • "1h"
                  • citations?: CitationsConfigParam | null
                    • enabled?: boolean
                  • context?: string | null
                  • title?: string | null
            • is_error?: boolean
          • ServerToolUseBlockParam
            • id: string
            • input: Record<string, unknown>
            • name: "web_search"
              • "web_search"
            • type: "server_tool_use"
              • "server_tool_use"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
          • WebSearchToolResultBlockParam
            • content: WebSearchToolResultBlockParamContent
              • Array<WebSearchResultBlockParam>
                • encrypted_content: string
                • title: string
                • type: "web_search_result"
                  • "web_search_result"
                • url: string
                • page_age?: string | null
              • WebSearchToolRequestError
                • error_code: "invalid_tool_input" | "unavailable" | "max_uses_exceeded" | 2 more
                  • "invalid_tool_input"
                  • "unavailable"
                  • "max_uses_exceeded"
                  • "too_many_requests"
                  • "query_too_long"
                • type: "web_search_tool_result_error"
                  • "web_search_tool_result_error"
            • tool_use_id: string
            • type: "web_search_tool_result"
              • "web_search_tool_result"
            • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
              • type: "ephemeral"
                • "ephemeral"
              • ttl?: "5m" | "1h" 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.
                • "5m"
                • "1h"
      • role: "user" | "assistant"
        • "user"
        • "assistant"
    • model: Model The model that will complete your prompt. See models for additional details and options.
      • "claude-opus-4-5-20251101" | "claude-opus-4-5" | "claude-3-7-sonnet-latest" | 17 more
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        • "claude-opus-4-5" Premium model combining maximum intelligence with practical performance
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        • "claude-3-7-sonnet-20250219" High-performance model with early extended thinking
        • "claude-3-5-haiku-latest" Fastest and most compact model for near-instant responsiveness
        • "claude-3-5-haiku-20241022" Our fastest model
        • "claude-haiku-4-5" Hybrid model, capable of near-instant responses and extended thinking
        • "claude-haiku-4-5-20251001" Hybrid model, capable of near-instant responses and extended thinking
        • "claude-sonnet-4-20250514" High-performance model with extended thinking
        • "claude-sonnet-4-0" High-performance model with extended thinking
        • "claude-4-sonnet-20250514" High-performance model with extended thinking
        • "claude-sonnet-4-5" Our best model for real-world agents and coding
        • "claude-sonnet-4-5-20250929" Our best model for real-world agents and coding
        • "claude-opus-4-0" Our most capable model
        • "claude-opus-4-20250514" Our most capable model
        • "claude-4-opus-20250514" Our most capable model
        • "claude-opus-4-1-20250805" Our most capable model
        • "claude-3-opus-latest" Excels at writing and complex tasks
        • "claude-3-opus-20240229" Excels at writing and complex tasks
        • "claude-3-haiku-20240307" Our previous most fast and cost-effective
      • (string & {})
    • metadata?: Metadata An object describing metadata about the request.
      • user_id?: string | null An external identifier for the user who is associated with the request. This should be a uuid, hash value, or other opaque identifier. Anthropic may use this id to help detect abuse. Do not include any identifying information such as name, email address, or phone number.
    • service_tier?: "auto" | "standard_only" 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.
      • "auto"
      • "standard_only"
    • stop_sequences?: Array<string> 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.
    • stream?: false Whether to incrementally stream the response using server-sent events. See streaming for details.
      • false
    • system?: string | Array<TextBlockParam> 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.
      • string
      • Array<TextBlockParam>
        • text: string
        • type: "text"
          • "text"
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
        • citations?: Array<TextCitationParam> | null
          • CitationCharLocationParam
            • cited_text: string
            • document_index: number
            • document_title: string | null
            • end_char_index: number
            • start_char_index: number
            • type: "char_location"
              • "char_location"
          • CitationPageLocationParam
            • cited_text: string
            • document_index: number
            • document_title: string | null
            • end_page_number: number
            • start_page_number: number
            • type: "page_location"
              • "page_location"
          • CitationContentBlockLocationParam
            • cited_text: string
            • document_index: number
            • document_title: string | null
            • end_block_index: number
            • start_block_index: number
            • type: "content_block_location"
              • "content_block_location"
          • CitationWebSearchResultLocationParam
            • cited_text: string
            • encrypted_index: string
            • title: string | null
            • type: "web_search_result_location"
              • "web_search_result_location"
            • url: string
          • CitationSearchResultLocationParam
            • cited_text: string
            • end_block_index: number
            • search_result_index: number
            • source: string
            • start_block_index: number
            • title: string | null
            • type: "search_result_location"
              • "search_result_location"
    • temperature?: number 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.
    • thinking?: ThinkingConfigParam 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.
      • ThinkingConfigEnabled
        • budget_tokens: number Determines how many tokens Claude can use for its internal reasoning process. Larger budgets can enable more thorough analysis for complex problems, improving response quality. Must be ≥1024 and less than max_tokens. See extended thinking for details.
        • type: "enabled"
          • "enabled"
      • ThinkingConfigDisabled
        • type: "disabled"
          • "disabled"
    • tool_choice?: ToolChoice 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.
      • ToolChoiceAuto The model will automatically decide whether to use tools.
        • type: "auto"
          • "auto"
        • disable_parallel_tool_use?: boolean Whether to disable parallel tool use. Defaults to false. If set to true, the model will output at most one tool use.
      • ToolChoiceAny The model will use any available tools.
        • type: "any"
          • "any"
        • disable_parallel_tool_use?: boolean Whether to disable parallel tool use. Defaults to false. If set to true, the model will output exactly one tool use.
      • ToolChoiceTool The model will use the specified tool with tool_choice.name.
        • name: string The name of the tool to use.
        • type: "tool"
          • "tool"
        • disable_parallel_tool_use?: boolean Whether to disable parallel tool use. Defaults to false. If set to true, the model will output exactly one tool use.
      • ToolChoiceNone The model will not be allowed to use tools.
        • type: "none"
          • "none"
    • tools?: Array<ToolUnion> 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.
      • Tool
        • input_schema: InputSchema 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"
            • "object"
          • properties?: Record<string, unknown> | null
          • required?: Array<string> | null
        • name: string Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
        • description?: string 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?: "custom" | null
          • "custom"
      • ToolBash20250124
        • name: "bash" Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
          • "bash"
        • type: "bash_20250124"
          • "bash_20250124"
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
      • ToolTextEditor20250124
        • name: "str_replace_editor" Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
          • "str_replace_editor"
        • type: "text_editor_20250124"
          • "text_editor_20250124"
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
      • ToolTextEditor20250429
        • name: "str_replace_based_edit_tool" Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
          • "str_replace_based_edit_tool"
        • type: "text_editor_20250429"
          • "text_editor_20250429"
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
      • ToolTextEditor20250728
        • name: "str_replace_based_edit_tool" Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
          • "str_replace_based_edit_tool"
        • type: "text_editor_20250728"
          • "text_editor_20250728"
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
        • max_characters?: number | null Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.
      • WebSearchTool20250305
        • name: "web_search" Name of the tool. This is how the tool will be called by the model and in tool_use blocks.
          • "web_search"
        • type: "web_search_20250305"
          • "web_search_20250305"
        • allowed_domains?: Array<string> | null If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.
        • blocked_domains?: Array<string> | null If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.
        • cache_control?: CacheControlEphemeral | null Create a cache control breakpoint at this content block.
          • type: "ephemeral"
            • "ephemeral"
          • ttl?: "5m" | "1h" 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.
            • "5m"
            • "1h"
        • max_uses?: number | null Maximum number of times the tool can be used in the API request.
        • user_location?: UserLocation | null Parameters for the user’s location. Used to provide more relevant search results.
          • type: "approximate"
            • "approximate"
          • city?: string | null The city of the user.
          • country?: string | null The two letter ISO country code of the user.
          • region?: string | null The region of the user.
          • timezone?: string | null The IANA timezone of the user.
    • top_k?: number 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.
    • top_p?: number 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.
  • MessageCreateParamsNonStreaming extends MessageCreateParamsBase
    • stream?: false Whether to incrementally stream the response using server-sent events. See streaming for details.
      • false
  • MessageCreateParamsNonStreaming extends MessageCreateParamsBase
    • stream?: false Whether to incrementally stream the response using server-sent events. See streaming for details.
      • false

​

Returns

• Message
  • id: string Unique object identifier. The format and length of IDs may change over time.
  • content: Array<ContentBlock> 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)"}]
    
    • TextBlock
      • citations: Array<TextCitation> | null 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.
        • CitationCharLocation
          • cited_text: string
          • document_index: number
          • document_title: string | null
          • end_char_index: number
          • file_id: string | null
          • start_char_index: number
          • type: "char_location"
            • "char_location"
        • CitationPageLocation
          • cited_text: string
          • document_index: number
          • document_title: string | null
          • end_page_number: number
          • file_id: string | null
          • start_page_number: number
          • type: "page_location"
            • "page_location"
        • CitationContentBlockLocation
          • cited_text: string
          • document_index: number
          • document_title: string | null
          • end_block_index: number
          • file_id: string | null
          • start_block_index: number
          • type: "content_block_location"
            • "content_block_location"
        • CitationsWebSearchResultLocation
          • cited_text: string
          • encrypted_index: string
          • title: string | null
          • type: "web_search_result_location"
            • "web_search_result_location"
          • url: string
        • CitationsSearchResultLocation
          • cited_text: string
          • end_block_index: number
          • search_result_index: number
          • source: string
          • start_block_index: number
          • title: string | null
          • type: "search_result_location"
            • "search_result_location"
      • text: string
      • type: "text"
        • "text"
    • ThinkingBlock
      • signature: string
      • thinking: string
      • type: "thinking"
        • "thinking"
    • RedactedThinkingBlock
      • data: string
      • type: "redacted_thinking"
        • "redacted_thinking"
    • ToolUseBlock
      • id: string
      • input: Record<string, unknown>
      • name: string
      • type: "tool_use"
        • "tool_use"
    • ServerToolUseBlock
      • id: string
      • input: Record<string, unknown>
      • name: "web_search"
        • "web_search"
      • type: "server_tool_use"
        • "server_tool_use"
    • WebSearchToolResultBlock
      • content: WebSearchToolResultBlockContent
        • WebSearchToolResultError
          • error_code: "invalid_tool_input" | "unavailable" | "max_uses_exceeded" | 2 more
            • "invalid_tool_input"
            • "unavailable"
            • "max_uses_exceeded"
            • "too_many_requests"
            • "query_too_long"
          • type: "web_search_tool_result_error"
            • "web_search_tool_result_error"
        • Array<WebSearchResultBlock>
          • encrypted_content: string
          • page_age: string | null
          • title: string
          • type: "web_search_result"
            • "web_search_result"
          • url: string
      • tool_use_id: string
      • type: "web_search_tool_result"
        • "web_search_tool_result"
  • model: Model The model that will complete your prompt. See models for additional details and options.
    • "claude-opus-4-5-20251101" | "claude-opus-4-5" | "claude-3-7-sonnet-latest" | 17 more
      • "claude-opus-4-5-20251101" Premium model combining maximum intelligence with practical performance
      • "claude-opus-4-5" Premium model combining maximum intelligence with practical performance
      • "claude-3-7-sonnet-latest" High-performance model with early extended thinking
      • "claude-3-7-sonnet-20250219" High-performance model with early extended thinking
      • "claude-3-5-haiku-latest" Fastest and most compact model for near-instant responsiveness
      • "claude-3-5-haiku-20241022" Our fastest model
      • "claude-haiku-4-5" Hybrid model, capable of near-instant responses and extended thinking
      • "claude-haiku-4-5-20251001" Hybrid model, capable of near-instant responses and extended thinking
      • "claude-sonnet-4-20250514" High-performance model with extended thinking
      • "claude-sonnet-4-0" High-performance model with extended thinking
      • "claude-4-sonnet-20250514" High-performance model with extended thinking
      • "claude-sonnet-4-5" Our best model for real-world agents and coding
      • "claude-sonnet-4-5-20250929" Our best model for real-world agents and coding
      • "claude-opus-4-0" Our most capable model
      • "claude-opus-4-20250514" Our most capable model
      • "claude-4-opus-20250514" Our most capable model
      • "claude-opus-4-1-20250805" Our most capable model
      • "claude-3-opus-latest" Excels at writing and complex tasks
      • "claude-3-opus-20240229" Excels at writing and complex tasks
      • "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".
    • "assistant"
  • stop_reason: StopReason | null 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.
    • "end_turn"
    • "max_tokens"
    • "stop_sequence"
    • "tool_use"
    • "pause_turn"
    • "refusal"
  • stop_sequence: string | null 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".
    • "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.
    • cache_creation: CacheCreation | null Breakdown of cached tokens by TTL
      • ephemeral_1h_input_tokens: number The number of input tokens used to create the 1 hour cache entry.
      • ephemeral_5m_input_tokens: number The number of input tokens used to create the 5 minute cache entry.
    • cache_creation_input_tokens: number | null The number of input tokens used to create the cache entry.
    • cache_read_input_tokens: number | null The number of input tokens read from the cache.
    • input_tokens: number The number of input tokens which were used.
    • output_tokens: number The number of output tokens which were used.
    • server_tool_use: ServerToolUsage | null The number of server tool requests.
      • web_search_requests: number The number of web search tool requests.
    • service_tier: "standard" | "priority" | "batch" | null If the request used the priority, standard, or batch tier.
      • "standard"
      • "priority"
      • "batch"

​

Example

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
  apiKey: process.env['ANTHROPIC_API_KEY'], // This is the default and can be omitted
});

const message = await client.messages.create({
  max_tokens: 1024,
  messages: [{ content: 'Hello, world', role: 'user' }],
  model: 'claude-sonnet-4-5-20250929',
});

console.log(message.id);