Claude Sonnet 4.5 · Messages

POST/v1/messages

Request parameters

Authorization

Add an Authorization header whose value is Bearer followed by your API key.

Authorization: Bearer ****************

anthropic-version: 2023-06-01

Header parameters

Content-TypestringOptional

application/json

AcceptstringOptional

application/json

Body parametersapplication/jsonrequired

modelstringRequired

Model ID, fixed to `claude-sonnet-4-5-20250929`

messagesarray[object]Required

List of conversation messages; each has `role` (user / assistant) and `content` (text or content blocks)

max_tokensintegerRequired

Maximum number of tokens to generate; required by the Anthropic API

systemstring | array[object]Optional

System prompt, passed as a top-level field (not a message)

temperaturenumberOptional

Sampling temperature; higher is more random

top_pnumberOptional

Nucleus sampling; alternative to `temperature`. Range `0`–`1`

top_kintegerOptional

Top-k sampling; limits candidates to the K most likely tokens

streambooleanOptional

Whether to stream the response (SSE), default `false`

stop_sequencesarray[string]Optional

Custom sequences that stop generation

toolsarray[object]Optional

Tool definitions for tool use

tool_choiceobjectOptional

Controls whether and which tool is used

metadataobjectOptional

Request metadata, such as `user_id`

thinkingobjectOptional

Thinking configuration; supported modes depend on the Claude model

Example

{
  "model": "claude-sonnet-4-5-20250929",
  "max_tokens": 1024,
  "messages": [
    {
      "role": "user",
      "content": "Hi, tell me about yourself"
    }
  ]
}

{  "model": "claude-sonnet-4-5-20250929",  "max_tokens": 1024,  "messages": [    {      "role": "user",      "content": "Hi, tell me about yourself"    }  ]}

Request code samples

curl https://api.hotrouter.ai/v1/messages \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-5-20250929",
    "max_tokens": 1024,
    "messages": [
      {
        "role": "user",
        "content": "Hi, tell me about yourself"
      }
    ]
  }'

curl https://api.hotrouter.ai/v1/messages \  -H "Authorization: Bearer $API_KEY" \  -H "Content-Type: application/json" \  -H "anthropic-version: 2023-06-01" \  -d '{    "model": "claude-sonnet-4-5-20250929",    "max_tokens": 1024,    "messages": [      {        "role": "user",        "content": "Hi, tell me about yourself"      }    ]  }'

Response

200 · Success

idstringRequired

Unique id of this response

typestringRequired

Object type (message)

rolestringRequired

Message role

contentarray[object]Required

Content blocks array

stop_reasonstringOptional

Finish reason (end_turn / max_tokens, etc.)

usageobjectRequired

Token usage of this call

Example

{
  "id": "msg_xxx",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hi! Nice to meet you…"
    }
  ],
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 12,
    "output_tokens": 24
  }
}

{  "id": "msg_xxx",  "type": "message",  "role": "assistant",  "content": [    {      "type": "text",      "text": "Hi! Nice to meet you…"    }  ],  "stop_reason": "end_turn",  "usage": {    "input_tokens": 12,    "output_tokens": 24  }}

Claude Sonnet 4.5 · Messages

Request parameters

Request code samples

Response

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