curl --request POST \
--url https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/messages \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data @- <<EOF
{
"message": "Also bump the timeout to 30s while you're in there.",
"client_message_id": "follow-up-018f6f3a"
}
EOFimport requests
url = "https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/messages"
payload = {
"message": "Also bump the timeout to 30s while you're in there.",
"client_message_id": "follow-up-018f6f3a"
}
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({
message: 'Also bump the timeout to 30s while you\'re in there.',
client_message_id: 'follow-up-018f6f3a'
})
};
fetch('https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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([
'message' => 'Also bump the timeout to 30s while you\'re in there.',
'client_message_id' => 'follow-up-018f6f3a'
]),
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/{sessionId}/messages"
payload := strings.NewReader("{\n \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\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/{sessionId}/messages")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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 \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\n}"
response = http.request(request)
puts response.read_body{
"ok": true,
"delivery": "<string>",
"continuation_session_id": "<string>",
"message_id": "<string>",
"client_message_id": "<string>",
"held_reason": "<string>"
}Send a message
Adds a follow-up instruction to a running or finished Session, including an owned subagent Session. Child continuations retain their original execution permissions. Device execution requires devices:use in addition to run, including continuations and pending Device handoffs.
Scope:runcurl --request POST \
--url https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/messages \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data @- <<EOF
{
"message": "Also bump the timeout to 30s while you're in there.",
"client_message_id": "follow-up-018f6f3a"
}
EOFimport requests
url = "https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/messages"
payload = {
"message": "Also bump the timeout to 30s while you're in there.",
"client_message_id": "follow-up-018f6f3a"
}
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({
message: 'Also bump the timeout to 30s while you\'re in there.',
client_message_id: 'follow-up-018f6f3a'
})
};
fetch('https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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([
'message' => 'Also bump the timeout to 30s while you\'re in there.',
'client_message_id' => 'follow-up-018f6f3a'
]),
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/{sessionId}/messages"
payload := strings.NewReader("{\n \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\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/{sessionId}/messages")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.reasonmachines.com/v3/organizations/{orgId}/sessions/{sessionId}/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 \"message\": \"Also bump the timeout to 30s while you're in there.\",\n \"client_message_id\": \"follow-up-018f6f3a\"\n}"
response = http.request(request)
puts response.read_body{
"ok": true,
"delivery": "<string>",
"continuation_session_id": "<string>",
"message_id": "<string>",
"client_message_id": "<string>",
"held_reason": "<string>"
}Authorizations
Your Reason API key from Settings › API keys. 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, network:read, network:write, automations:read, automations:write, agent_auth:read. network:read and network:write are opt-in, excluded from default keys. network:read reads the saved workspace network policy; network:write replaces custom allowed hosts and requires a current organization owner/admin. Legacy project PATCH requests containing network_allowed_hosts also require network:write plus their existing run scope and project management permission; saved project hosts do not affect current session egress. Only owners/admins can mint or manage keys with network:write; keys cannot grant themselves more authority. See /docs/network-policies for replacement semantics and runtime applicability. 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).
Headers
Optional self-reported caller agent name. If absent, the server uses the User-Agent for external callers.
80Path Parameters
Organization id or slug. Resolve it with GET /v3/self.
The session id, returned as session_id by createSession and listSessions.
Body
The follow-up instruction for the agent. It reaches the running turn or starts the next one; the response's delivery says which.
Up to 10 attachments; maximum 64 MiB per file and 80 MiB total decoded bytes. The endpoint's request-body limit also applies to the encoded payload.
- Option 1
- Option 2
Show child attributes
Show child attributes
Caller-generated idempotency key. Reusing it for the same Session returns the original accepted turn.
1 - 160Optional model id from GET /agent-auth/models to retry this session on. A model override always starts a new continuation run, because a run's model is fixed at its first execution. Omit or use auto to keep the session's current model.
How much reasoning the model should use for the follow-up turn. Higher effort trades time and token usage for more deliberation; supported levels depend on the selected model. Omit to retain the Session's effort setting.
minimal, low, medium, high, xhigh, max Same as the create field, for this and later turns: the follow-up goes on with the provider's other accounts, then Reason, when the Session's subscription or key runs out. A Session that already rolls over keeps doing so.
While a turn runs: steer (the default) hands the message to the running turn; queue holds it until the turn ends and then runs it as the next one. A queued message can be sent at once or withdrawn with its message_id (POST .../messages/{messageId}/steer, DELETE .../messages/{messageId}/queued). Not combinable with target.
steer, queue Moves the Session: this message's turn, and every later one, runs on this target instead of the one the Session was on. Same shape and admission as the create target (cloud, a Device and root, or a named Machine). Only the conversation moves; files on the previous machine do not, unless they were pushed to the Session branch. A move starts a new continuation run, so the Session must have finished its current turn. Any target other than cloud needs the devices:use scope.
- Option 1
- Option 2
- Option 3
- Option 4
Show child attributes
Show child attributes
Response
Message accepted and delivered or queued for a continuation.
True: the message was accepted.
How the message was delivered: steered_live (into the running turn), queued_for_next_turn or held_in_queue (waits for the turn to end), started_continuation_run or reattached_warm_session (started a new turn), applied_to_queued_run, saved_for_follow_up (saved; see held_reason), queue_cancelled or continuation_blocked.
The stable logical Session id after an accepted follow-up. Continue polling this id; Reason may run the turn in a hidden execution Attempt.
Set for a message sent with delivery queue: the id to send it at once or withdraw it while it waits.
The message's idempotency key: the client_message_id sent, or the one the server gave it. Resending the message with it returns this accepted turn instead of adding another.
Present when delivery is saved_for_follow_up and the message is waiting instead of starting. session_machine_transition_pending: the Session's machine is changing; the message is delivered when the change settles, so do not send it again. If the change has not settled after 10 minutes the message is marked not delivered instead.

