---
title: "Send thread message"
method: POST
path: "/v1/threads/{threadId}/message"
tags: ["threads"]
---

# Send thread message

`POST /v1/threads/{threadId}/message`

Send a message to an existing thread.

## Path parameters

- `threadId` string, required

## Request body

- SendThreadMessageBody
  - `impersonateUserEmail` string, email
  - `messageId` string
  - `message` string, required
  - `mode` 'interrupt' | 'queue'
  - `model` 'claude-fable-5' | 'claude-opus-5' | 'claude-sonnet-5' | 'claude-opus-4-8' | 'claude-opus-4-7' | 'claude-opus-4-6' | 'claude-opus-4-5' | 'claude-sonnet-4-6' | 'claude-haiku-4-5' | 'gpt-5.6-sol' | 'gpt-5.6-terra' | 'gpt-5.6-luna' | 'gpt-5.5' | 'gpt-5.5-pro' | 'gpt-5.4' | 'gpt-5.4-mini' | 'gpt-5.3-codex' | 'gpt-5.3-codex-spark' | 'gemini-3.1-pro-preview' | 'gemini-3-flash-preview' | 'grok-4-1-fast' | 'grok-4-5' | 'composer-2.5-fast' | 'glm-5.2' | 'glm-5.1' | 'glm-5v-turbo' | 'deepseek-v4-pro' | 'glm-5-turbo' | 'glm-4.7' | 'kimi-k3' | 'kimi-k2.7-code' | 'kimi-k2.6' | 'qwen3-coder'
  - `speed` 'fast' | 'standard'
  - `reasoning` object
    - `mode` 'off' | 'on' | 'none' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh' | 'max', required
  - `buildModel` 'claude-fable-5' | 'claude-opus-5' | 'claude-sonnet-5' | 'claude-opus-4-8' | 'claude-opus-4-7' | 'claude-opus-4-6' | 'claude-opus-4-5' | 'claude-sonnet-4-6' | 'claude-haiku-4-5' | 'gpt-5.6-sol' | 'gpt-5.6-terra' | 'gpt-5.6-luna' | 'gpt-5.5' | 'gpt-5.5-pro' | 'gpt-5.4' | 'gpt-5.4-mini' | 'gpt-5.3-codex' | 'gpt-5.3-codex-spark' | 'gemini-3.1-pro-preview' | 'gemini-3-flash-preview' | 'grok-4-1-fast' | 'grok-4-5' | 'composer-2.5-fast' | 'glm-5.2' | 'glm-5.1' | 'glm-5v-turbo' | 'deepseek-v4-pro' | 'glm-5-turbo' | 'glm-4.7' | 'kimi-k3' | 'kimi-k2.7-code' | 'kimi-k2.6' | 'qwen3-coder'
  - `buildSpeed` 'fast' | 'standard'
  - `buildReasoning` object
    - `mode` 'off' | 'on' | 'none' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh' | 'max', required
  - `browserSnapshotIds` string[]
  - `attachmentUrls` string[]

## Response `200`

Success

- SendMessageResponse
  - `id` string, required
  - `status` 'sent' | 'queued' | 'pending', required
  - `inputEventId` string
  - `timelineSequence` string
  - `appendState` 'inserted' | 'already_present'

## Other responses

- `401` — Unauthorized
- `403` — Forbidden
- `404` — Not found
- `409` — Conflict
- `422` — Validation error
- `429` — Too many requests
- `500` — Internal error

## Changes

- **2026-07-26** `c9ea28cb32b6` — 4 info
  - added the new `claude-opus-5` enum value to the request property `buildModel`
  - added the new `claude-opus-5` enum value to the request property `model`
  - added the new `kimi-k3` enum value to the request property `buildModel`
  - added the new `kimi-k3` enum value to the request property `model`

[Change history](https://skmtc.dev/capy/apis/capy-api/changes/v1/threads/:threadId/message/post.md)

---

[API](https://skmtc.dev/capy/apis/capy-api.md) · [All operations](https://skmtc.dev/capy/apis/capy-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/capy/capy-api/revisions/c9ea28cb32b6/schema)