Start a new session's machine ahead of its create
curl --request POST \
--url https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"client_session_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}
'import requests
url = "https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart"
payload = { "client_session_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a" }
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({client_session_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a'})
};
fetch('https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart', 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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart",
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([
'client_session_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a'
]),
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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart"
payload := strings.NewReader("{\n \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart")
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 \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}"
response = http.request(request)
puts response.read_body{
"status": "starting",
"ttl_ms": 123
}{
"error": "prompt_required"
}{
"error": "missing_bearer",
"message": "Authorization required"
}{
"error": "missing_scope",
"required_scope": "sessions:read"
}{
"error": {
"type": "rate_limited",
"message": "This API key exceeded its request-rate limit"
}
}Sessions
Start a new session's machine ahead of its create
Reserve a Session id (a fresh UUID v4) and start its cloud machine while the prompt is still being written; pass the same id as client_session_id to create within 75 s and the session starts on the warm machine. Advisory and only for enabled workspaces: 204 means nothing was started, and create works the same either way. An unused machine is removed after 90 s.
runPOST
/
v3
/
organizations
/
{orgId}
/
sessions
/
prestart
Start a new session's machine ahead of its create
curl --request POST \
--url https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"client_session_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}
'import requests
url = "https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart"
payload = { "client_session_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a" }
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({client_session_id: '3c90c3cc-0d44-4b50-8888-8dd25736052a'})
};
fetch('https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart', 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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart",
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([
'client_session_id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a'
]),
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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart"
payload := strings.NewReader("{\n \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\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.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/prestart")
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 \"client_session_id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n}"
response = http.request(request)
puts response.read_body{
"status": "starting",
"ttl_ms": 123
}{
"error": "prompt_required"
}{
"error": "missing_bearer",
"message": "Authorization required"
}{
"error": "missing_scope",
"required_scope": "sessions:read"
}{
"error": {
"type": "rate_limited",
"message": "This API key exceeded its request-rate limit"
}
}Authorizations
Your Reason API key from Settings > API. New keys use reason_; legacy ara_ keys remain accepted. Keys are capability-scoped: run, mcp:read, mcp:write, secrets:read, secrets:write, sessions:read, sessions:debug, knowledge:read, memory:read, memory:write, skills:read, skills:write, repos:read, repos:write, reviews:read, reviews:write, deployment:read, analytics:read, org:read, org:write, attachments:read, attachments:write, guardrails:read, guardrails:write, automations:read, automations:write, agent_auth:read. mcp:write manages MCP server configuration only; it does not authorize remote MCP-tool execution. sessions:read reads sessions, including the assistant, reasoning and tool activity in their events. sessions:debug is privileged: only for organization owners/admins, it expands session events to the full diagnostic projection (diagnostic event kinds, status text and raw event metadata).
Path Parameters
Organization id or slug. Resolve it with GET /v3/self.
Body
application/json
A fresh UUID v4; send it as client_session_id on createSession.