diff --git a/.changeset/chat-agent-action-trigger-type.md b/.changeset/chat-agent-action-trigger-type.md
new file mode 100644
index 000000000..050951c02
--- /dev/null
+++ b/.changeset/chat-agent-action-trigger-type.md
@@ -0,0 +1,5 @@
+---
+"@trigger.dev/sdk": patch
+---
+
+Include `"action"` in the `ChatTaskPayload.trigger` union. `run()` is invoked with `trigger: "action"` after `onAction` processes a typed action, but the type previously omitted it. Users can now cleanly short-circuit the LLM call for actions that don't need a response (e.g. user-initiated compaction): `if (trigger === "action") return;`.
diff --git a/packages/trigger-sdk/src/v3/ai.ts b/packages/trigger-sdk/src/v3/ai.ts
index ab6709181..398ef7db7 100644
--- a/packages/trigger-sdk/src/v3/ai.ts
+++ b/packages/trigger-sdk/src/v3/ai.ts
@@ -626,8 +626,12 @@ export type ChatTaskPayload<TClientData = unknown> = {
    * - `"submit-message"`: A new user message
    * - `"regenerate-message"`: Regenerate the last assistant response
    * - `"preload"`: Run was preloaded before the first message (only on turn 0)
+   * - `"action"`: A typed action from the frontend (see `actionSchema` + `onAction`).
+   *   The action has already been applied before `run()` fires — check `trigger === "action"`
+   *   to short-circuit the LLM call when an action doesn't need a response.
+   * - `"close"`: The chat session is being closed (internal; `run()` is not called).
    */
-  trigger: "submit-message" | "regenerate-message" | "preload" | "close";
+  trigger: "submit-message" | "regenerate-message" | "preload" | "action" | "close";
 
   /** The ID of the message to regenerate (only for `"regenerate-message"`) */
   messageId?: string;