--- title: "Create message" method: POST path: "/messages" tags: ["Messages"] --- # Create message `POST /messages` ## Request - Base URL: `https://ai.megallm.io/v1` - URL: `https://ai.megallm.io/v1/messages` - Auth: API key in header `x-api-key` Create conversational messages using the Anthropic-compatible Messages API ## Headers - `anthropic-version` string, required - `anthropic-beta` string ## Request body - MessageRequest - `model` string, required: The model that will complete your prompt. See the list of Claude models at https://docs.claude.com/en/docs/about-claude/models - `messages` AnthropicMessage[], required: Input messages. Alternating user and assistant conversational turns. The first message must use the user role. Text content is the only format supported for the first user message. - `role` 'user' | 'assistant', required: The role of the messages author - `content` union, required - string: Plain text content - AnthropicContentBlock[]: Array of content blocks (text, image, tool_use, tool_result) - union - object: Text content block - `type` 'text', required - `text` string, required - `cache_control` object - … - object: Image content block - `type` 'image', required - `source` object, required - … - `cache_control` object - … - object: Tool use content block - `type` 'tool_use', required - `id` string, required: A unique identifier for this particular tool use block - `name` string, required: The name of the tool being used - `input` object, required: An object containing the input being passed to the tool - object: Tool result content block - `type` 'tool_result', required - `tool_use_id` string, required: The id of the tool use request this is a result for - `content` union, required: The result of the tool use - … - `is_error` boolean: Set to true if the tool execution resulted in an error - `cache_control` object - … - `max_tokens` integer, required: The maximum number of tokens to generate before stopping. Note that Claude may stop before reaching this maximum. This parameter only specifies the absolute maximum number of tokens to generate. - `system` union: System prompt. A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. - string: System prompt as plain text - object[]: Array of system content blocks - `type` 'text', required - `text` string, required - `cache_control` object - `type` 'ephemeral' - `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. - `top_p` number: Use nucleus sampling. In nucleus sampling, Claude computes the cumulative distribution over all the options for each subsequent token in decreasing probability order and cuts it off once it reaches a particular probability specified by top_p. - `top_k` integer: Only sample from the top K options for each subsequent token. Used to remove "long tail" low probability responses. Recommended for advanced use cases only. You usually only need to use temperature. - `stream` boolean: Whether to incrementally stream the response using server-sent events. See streaming documentation for details. - `stop_sequences` string[]: Custom text sequences that will cause the model to stop generating. Claude will stop when it encounters any of these strings. - `tools` AnthropicTool[]: 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. - `name` string, required: The name of the tool. Must be a-z, A-Z, 0-9, or contain underscores and dashes, with a maximum length of 64. - `description` string: Description of what this tool does. Tool descriptions should be as detailed as possible. - `input_schema` object, required: JSON schema for the tool input shape that the model will produce in tool_use output content blocks. - `type` 'object', required - `properties` object, required - `required` string[] - `cache_control` object - `type` 'ephemeral' - `tool_choice` union: How the model should use the provided tools. The model can use a specific tool, any available tool, or decide by itself. - object: allows Claude to decide whether to call any provided tools or not - `type` 'auto', required - object: tells Claude that it must use one of the provided tools - `type` 'any', required - object: allows Claude to use only the specified tool - `type` 'tool', required - `name` string, required - `thinking` object: Enable extended thinking by Claude. When enabled, Claude will think through the problem before responding. - `type` 'enabled' - `budget_tokens` integer: Maximum number of tokens to spend on thinking - `service_tier` 'auto' | 'standard_only': The service tier to use for the request. 'auto' lets us choose the tier, 'standard_only' restricts to standard tier. - `metadata` object: An object describing metadata about the request - `user_id` string: An external identifier for the user who is associated with the request ## Response `200` Successful response - MessageResponse - `id` string, required: Unique object identifier. The format and length of IDs may change over time. - `type` 'message', required: Object type. For Messages, this is always 'message'. - `role` 'assistant', required: Conversational role of the generated message. This is always 'assistant'. - `content` AnthropicResponseContentBlock[], required: Content generated by the model. This is an array of content blocks, each of which has a type that determines its shape. - union - object: Text content block in response - `type` 'text', required - `text` string, required: The text content - object: Thinking content block showing Claude's reasoning process - `type` 'thinking', required - `thinking` string, required: Claude's internal thinking process - object: Tool use content block - `type` 'tool_use', required - `id` string, required: A unique identifier for this particular tool use block - `name` string, required: The name of the tool being used - `input` object, required: An object containing the input being passed to the tool - `model` string, required: The model that handled the request. - `stop_reason` 'end_turn' | 'max_tokens' | 'stop_sequence' | 'tool_use', required: The reason that we stopped. This may be one of 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), or tool_use (the model invoked one or more tools). - `stop_sequence` string, nullable: 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. - `usage` object, required: Billing and rate-limit usage. Anthropic's API bills and rate-limits by token counts, as tokens represent the underlying cost to our systems. - `input_tokens` integer, required: The number of input tokens which were used. - `output_tokens` integer, required: The number of output tokens which were used. - `cache_creation_input_tokens` integer: The number of input tokens used to create the cache entry. - `cache_read_input_tokens` integer: The number of input tokens read from the cache. ## Other responses - `400`: Bad request - Invalid parameters - `401`: Unauthorized - Invalid or missing API key - `429`: Rate limit exceeded - `500`: Internal server error --- [API](https://skmtc.dev/megallm/apis/megallm-api.md) - [All operations](https://skmtc.dev/megallm/apis/megallm-api/llms.txt) - [OpenAPI document](https://skmtc.dev/megallm/apis/megallm-api/revisions/a365a5b98d60?raw)