Create a message (Anthropic Messages API)
curl --request POST \
--url https://api.impossibl.com/v1/messages \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"model": "claude-haiku-4-5",
"max_tokens": 123,
"messages": [
{
"content": "<string>"
}
],
"system": "<string>",
"stream": false,
"temperature": 123,
"top_p": 123,
"top_k": 123,
"stop_sequences": [
"<string>"
],
"thinking": {
"type": "enabled",
"budget_tokens": 1025
},
"output_config": {},
"tools": [
{
"name": "<string>",
"input_schema": {},
"description": "<string>"
}
],
"tool_choice": {
"name": "<string>"
}
}
'import requests
url = "https://api.impossibl.com/v1/messages"
payload = {
"model": "claude-haiku-4-5",
"max_tokens": 123,
"messages": [{ "content": "<string>" }],
"system": "<string>",
"stream": False,
"temperature": 123,
"top_p": 123,
"top_k": 123,
"stop_sequences": ["<string>"],
"thinking": {
"type": "enabled",
"budget_tokens": 1025
},
"output_config": {},
"tools": [
{
"name": "<string>",
"input_schema": {},
"description": "<string>"
}
],
"tool_choice": { "name": "<string>" }
}
headers = {
"Authorization": "Bearer <token>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
body: JSON.stringify({
model: 'claude-haiku-4-5',
max_tokens: 123,
messages: [{content: '<string>'}],
system: '<string>',
stream: false,
temperature: 123,
top_p: 123,
top_k: 123,
stop_sequences: ['<string>'],
thinking: {type: 'enabled', budget_tokens: 1025},
output_config: {},
tools: [{name: '<string>', input_schema: {}, description: '<string>'}],
tool_choice: {name: '<string>'}
})
};
fetch('https://api.impossibl.com/v1/messages', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.impossibl.com/v1/messages",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'model' => 'claude-haiku-4-5',
'max_tokens' => 123,
'messages' => [
[
'content' => '<string>'
]
],
'system' => '<string>',
'stream' => false,
'temperature' => 123,
'top_p' => 123,
'top_k' => 123,
'stop_sequences' => [
'<string>'
],
'thinking' => [
'type' => 'enabled',
'budget_tokens' => 1025
],
'output_config' => [
],
'tools' => [
[
'name' => '<string>',
'input_schema' => [
],
'description' => '<string>'
]
],
'tool_choice' => [
'name' => '<string>'
]
]),
CURLOPT_HTTPHEADER => [
"Authorization: Bearer <token>",
"Content-Type: application/json"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.impossibl.com/v1/messages"
payload := strings.NewReader("{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("Authorization", "Bearer <token>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.impossibl.com/v1/messages")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.impossibl.com/v1/messages")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}"
response = http.request(request)
puts response.read_body{
"id": "msg_...",
"type": "message",
"role": "assistant",
"model": "<string>",
"content": [
{
"type": "text",
"text": "<string>",
"id": "<string>",
"name": "<string>",
"input": {}
}
],
"stop_reason": "end_turn",
"stop_sequence": "<string>",
"usage": {
"speed": "fast",
"input_tokens": 123,
"output_tokens": 123
}
}{
"error": {
"message": "`model` and `messages` are required",
"type": "invalid_request_error"
}
}{
"error": {
"message": "Invalid API key",
"type": "authentication_error"
}
}{
"error": {
"message": "Insufficient credits. Top up to continue.",
"type": "insufficient_quota"
}
}{
"error": {
"message": "Unknown model: foo/bar",
"type": "invalid_request_error"
}
}{
"error": {
"message": "permission-denied: ...",
"type": "upstream_error"
}
}{
"error": {
"message": "Provider not configured: missing OPENAI_API_KEY",
"type": "provider_not_configured"
}
}API Reference
Create a message (Anthropic Messages API)
Drop-in compatible with Anthropic’s Messages API. Authenticate with x-api-key (or Authorization: Bearer). A bare model id like claude-haiku-4-5 routes to Anthropic; use provider/model for others. Set stream: true for SSE.
POST
/
v1
/
messages
Create a message (Anthropic Messages API)
curl --request POST \
--url https://api.impossibl.com/v1/messages \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"model": "claude-haiku-4-5",
"max_tokens": 123,
"messages": [
{
"content": "<string>"
}
],
"system": "<string>",
"stream": false,
"temperature": 123,
"top_p": 123,
"top_k": 123,
"stop_sequences": [
"<string>"
],
"thinking": {
"type": "enabled",
"budget_tokens": 1025
},
"output_config": {},
"tools": [
{
"name": "<string>",
"input_schema": {},
"description": "<string>"
}
],
"tool_choice": {
"name": "<string>"
}
}
'import requests
url = "https://api.impossibl.com/v1/messages"
payload = {
"model": "claude-haiku-4-5",
"max_tokens": 123,
"messages": [{ "content": "<string>" }],
"system": "<string>",
"stream": False,
"temperature": 123,
"top_p": 123,
"top_k": 123,
"stop_sequences": ["<string>"],
"thinking": {
"type": "enabled",
"budget_tokens": 1025
},
"output_config": {},
"tools": [
{
"name": "<string>",
"input_schema": {},
"description": "<string>"
}
],
"tool_choice": { "name": "<string>" }
}
headers = {
"Authorization": "Bearer <token>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
body: JSON.stringify({
model: 'claude-haiku-4-5',
max_tokens: 123,
messages: [{content: '<string>'}],
system: '<string>',
stream: false,
temperature: 123,
top_p: 123,
top_k: 123,
stop_sequences: ['<string>'],
thinking: {type: 'enabled', budget_tokens: 1025},
output_config: {},
tools: [{name: '<string>', input_schema: {}, description: '<string>'}],
tool_choice: {name: '<string>'}
})
};
fetch('https://api.impossibl.com/v1/messages', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.impossibl.com/v1/messages",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'model' => 'claude-haiku-4-5',
'max_tokens' => 123,
'messages' => [
[
'content' => '<string>'
]
],
'system' => '<string>',
'stream' => false,
'temperature' => 123,
'top_p' => 123,
'top_k' => 123,
'stop_sequences' => [
'<string>'
],
'thinking' => [
'type' => 'enabled',
'budget_tokens' => 1025
],
'output_config' => [
],
'tools' => [
[
'name' => '<string>',
'input_schema' => [
],
'description' => '<string>'
]
],
'tool_choice' => [
'name' => '<string>'
]
]),
CURLOPT_HTTPHEADER => [
"Authorization: Bearer <token>",
"Content-Type: application/json"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.impossibl.com/v1/messages"
payload := strings.NewReader("{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("Authorization", "Bearer <token>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.impossibl.com/v1/messages")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.impossibl.com/v1/messages")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"model\": \"claude-haiku-4-5\",\n \"max_tokens\": 123,\n \"messages\": [\n {\n \"content\": \"<string>\"\n }\n ],\n \"system\": \"<string>\",\n \"stream\": false,\n \"temperature\": 123,\n \"top_p\": 123,\n \"top_k\": 123,\n \"stop_sequences\": [\n \"<string>\"\n ],\n \"thinking\": {\n \"type\": \"enabled\",\n \"budget_tokens\": 1025\n },\n \"output_config\": {},\n \"tools\": [\n {\n \"name\": \"<string>\",\n \"input_schema\": {},\n \"description\": \"<string>\"\n }\n ],\n \"tool_choice\": {\n \"name\": \"<string>\"\n }\n}"
response = http.request(request)
puts response.read_body{
"id": "msg_...",
"type": "message",
"role": "assistant",
"model": "<string>",
"content": [
{
"type": "text",
"text": "<string>",
"id": "<string>",
"name": "<string>",
"input": {}
}
],
"stop_reason": "end_turn",
"stop_sequence": "<string>",
"usage": {
"speed": "fast",
"input_tokens": 123,
"output_tokens": 123
}
}{
"error": {
"message": "`model` and `messages` are required",
"type": "invalid_request_error"
}
}{
"error": {
"message": "Invalid API key",
"type": "authentication_error"
}
}{
"error": {
"message": "Insufficient credits. Top up to continue.",
"type": "insufficient_quota"
}
}{
"error": {
"message": "Unknown model: foo/bar",
"type": "invalid_request_error"
}
}{
"error": {
"message": "permission-denied: ...",
"type": "upstream_error"
}
}{
"error": {
"message": "Provider not configured: missing OPENAI_API_KEY",
"type": "provider_not_configured"
}
}Authorizations
BearerKeyApiKeyHeader
Gateway API key (imp-rt-...) from POST /v1/accounts or /v1/keys.
Body
application/json
Example:
"claude-haiku-4-5"
Required by the Anthropic API.
Show child attributes
Show child attributes
Fast inference, available only for claude-opus-5-5 via native Anthropic. Standard is a no-op. Unsupported models and incompatible deployment pins return 400. Anthropic service_tier is a separate Priority Tier control and does not select Fast. No automatic downgrade on capacity errors.
Available options:
fast, standard Top-level system prompt.
Anthropic thinking control, preserved on native Anthropic and Bedrock routes.
- Option 1
- Option 2
- Option 3
Show child attributes
Show child attributes
Show child attributes
Show child attributes
Tools the model may call (relay mode — the gateway does not execute them).
Show child attributes
Show child attributes
{ type: auto }, { type: any }, { type: tool, name }, or { type: none }.
Show child attributes
Show child attributes
Request-level breakpoint. Not part of Anthropic's own API — accepted so all three surfaces behave alike. A per-block cache_control anywhere, system included, takes precedence and this is ignored.
Show child attributes
Show child attributes
Response
A message object. When stream: true, the body is an SSE stream of
Anthropic events (message_start, content_block_delta, …, message_stop).
Non-streaming Anthropic message response.
Example:
"msg_..."
Allowed value:
"message"Allowed value:
"assistant"Text blocks and, when the model calls a tool, tool_use blocks.
Show child attributes
Show child attributes
Available options:
end_turn, max_tokens, stop_sequence, tool_use Show child attributes
Show child attributes
⌘I