> ## Documentation Index
> Fetch the complete documentation index at: https://ara-90a60a07.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# 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: `run`
## OpenAPI
````yaml /openapi.json post /v3/organizations/{orgId}/sessions/{sessionId}/messages
openapi: 3.1.0
info:
title: Reason Machines API
version: 3.0.0
description: >-
The Reason HTTP API. Drive cloud software-engineering agents: open sessions
against your repositories, stream their work, and manage the secrets,
knowledge, skills, and automations they run with.
Authenticate with a Reason API key sent as a bearer token. New keys use
`reason_`; legacy `ara_` keys remain accepted. Every resource is scoped to
an organization; resolve your `org_id` once with `GET /v3/self`.
servers:
- url: https://api.reasonmachines.ai
security:
- araApiKey: []
tags:
- name: Devices
description: >-
Owned Mac and headless Device identity, bounded enrollment and root
grants.
- name: Account
description: Verify a key and resolve the organization it belongs to.
- name: Projects
description: >-
Discover existing workspace projects to target when creating and listing
sessions.
- name: Sessions
description: >-
A session is one run of an agent against a repository: it reproduces the
task, writes the code, verifies it, and opens a pull request or merge
request.
- name: Secrets
description: >-
Encrypted credentials injected into the agent's sandbox. Write-only:
values can be set but never read back.
- name: Knowledge
description: Durable notes the agent consults while it works.
- name: Memory
description: >-
Editable repository notes that are projected into native memory; generated
memory remains read-only.
- name: Skills
description: >-
Reusable instruction bundles Reason selects semantically from their
descriptions for matching agent tasks.
- name: Automations
description: Recurring or one-time triggers that open sessions on a timetable.
- name: Change Request Reviews
description: >-
Automated senior-engineer reviews posted on pull requests and merge
requests.
- name: Repositories
description: Connected repositories, their indexing state, and generated wikis.
- name: Git Connections
description: Linked source-control accounts and the repositories they expose.
- name: Consumption
description: 'Billing-aligned usage: daily consumption and billing cycles.'
- name: Metrics
description: Aggregate analytics over sessions, change requests, and usage.
- name: Audit Logs
description: An append-only record of changes made within the organization.
- name: Organizations
description: The top-level tenant. Create, read, update, and delete organizations.
- name: Members
description: People in an organization and their pending invites.
- name: Service Users
description: Machine principals that own API keys for headless access.
- name: Roles
description: Role assignments that govern what each member can do.
- name: Attachments
description: >-
Files uploaded to the organization and shared with sessions, downloaded
via short-lived signed URLs.
- name: Guardrails
description: >-
Per-repository automation limits and the violations recorded when a limit
is hit.
- name: MCP Servers
description: >-
Org-level Model Context Protocol servers exposed to the agent. Secret
values are write-only.
- name: Settings
description: 'Organization configuration: namespaced settings and the run tag policy.'
- name: Blueprints
description: >-
Read-only declarative manifests of an organization's agents (identity, run
config, triggers, suite), with credentials redacted.
- name: IP Access List
description: >-
Source-network allow-list that, when enabled, restricts the organization's
API surface to a set of CIDR ranges.
- name: Groups
description: Manually-curated member groups carrying optional per-day resource limits.
- name: Provider Credentials
description: >-
Configure Bring-Your-Own-Key (BYOK) API keys and subscription credentials
for model providers. Secret values are write-only.
paths:
/v3/organizations/{orgId}/sessions/{sessionId}/messages:
parameters:
- $ref: '#/components/parameters/orgId'
- name: sessionId
description: The session id.
in: path
required: true
schema:
type: string
post:
tags:
- Sessions
summary: Send a message
description: >-
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: `run`
operationId: sendSessionMessage
requestBody:
required: true
content:
application/json:
schema:
type: object
properties:
message:
type: string
description: Follow-up instruction, at most 2 MiB when UTF-8 encoded.
client_message_id:
type: string
minLength: 1
maxLength: 160
description: >-
Caller-generated idempotency key. Reusing it for the same
Session returns the original accepted turn.
model:
type: string
description: >-
Optional 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.
reasoning_effort:
type: string
enum:
- minimal
- low
- medium
- high
- xhigh
- max
description: >-
Optional reasoning effort override applied to the
continuation run.
required:
- message
example:
message: Also bump the timeout to 30s while you're in there.
client_message_id: follow-up-018f6f3a
responses:
'200':
description: Message accepted and delivered or queued for a continuation.
content:
application/json:
schema:
$ref: '#/components/schemas/SendSessionMessageResponse'
'400':
description: >-
The message was empty, or a supplied `model` / `reasoning_effort`
override was not valid.
content:
application/json:
schema:
type: object
required:
- error
properties:
error:
type: string
enum:
- message_required
- invalid_model
- invalid_reasoning_effort
'402':
description: >-
An active paid plan or valid trial is required
(ara_subscription_required).
content:
application/json:
schema:
type: object
required:
- error
- reason
- message
properties:
error:
type: string
enum:
- quota_exhausted
reason:
type: string
message:
type: string
'403':
description: >-
The caller lacks a required scope, including devices:use for Device
execution, or does not own the subagent Session and its parent
(subagent_message_forbidden).
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
'404':
$ref: '#/components/responses/NotFound'
'409':
description: >-
The subagent Session lineage is invalid (subagent_lineage_invalid),
its execution target is temporarily unavailable, the Session is
briefly unavailable while a newly attached repository becomes
executable, a model override requires a finished Session, or the
supplied idempotency key was previously used for a different
message.
content:
application/json:
schema:
type: object
required:
- error
- message
properties:
error:
type: string
message:
type: string
'503':
description: >-
Session writes are disabled, runtime preflight is unavailable, or
the message could not be recorded with its required steering audit
entry.
content:
application/json:
schema:
type: object
required:
- error
properties:
error:
type: string
enum:
- cloud_agents_disabled
- runtime_preflight_unavailable
- steering_audit_unavailable
security:
- araApiKey:
- run
components:
parameters:
orgId:
name: orgId
in: path
required: true
description: Organization id or slug. Resolve it with `GET /v3/self`.
schema:
type: string
schemas:
SendSessionMessageResponse:
type: object
properties:
ok:
type: boolean
delivery:
type: string
continuation_session_id:
description: >-
The stable logical Session id after an accepted follow-up. Continue
polling this id; Ara may run the turn in a hidden execution Attempt.
type:
- string
- 'null'
required:
- ok
Error:
type: object
properties:
error:
type: string
message:
type: string
required_scope:
type: string
description: >-
The capability required when the request was denied for a missing
scope.
responses:
NotFound:
description: Resource not found.
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
example:
error: session_not_found
securitySchemes:
araApiKey:
type: http
scheme: bearer
bearerFormat: 'reason_ (legacy: ara_)'
description: >-
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:debug is privileged: it expands diagnostic session events only
for organization owners/admins.
````