diff --git a/packages/sdk/openapi.json b/packages/sdk/openapi.json
index 6e350a71e..62296d37f 100644
--- a/packages/sdk/openapi.json
+++ b/packages/sdk/openapi.json
@@ -1568,6 +1568,77 @@
         ]
       }
     },
+    "/experimental/session/{sessionID}/background": {
+      "post": {
+        "tags": ["experimental"],
+        "operationId": "experimental.session.background",
+        "parameters": [
+          {
+            "name": "sessionID",
+            "in": "path",
+            "schema": {
+              "type": "string",
+              "pattern": "^ses"
+            },
+            "required": true
+          },
+          {
+            "name": "directory",
+            "in": "query",
+            "schema": {
+              "type": "string"
+            },
+            "required": false
+          },
+          {
+            "name": "workspace",
+            "in": "query",
+            "schema": {
+              "type": "string"
+            },
+            "required": false
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Backgrounded subagents",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "boolean",
+                  "description": "Backgrounded subagents"
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "BadRequest | InvalidRequestError",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "anyOf": [
+                    {
+                      "$ref": "#/components/schemas/effect_HttpApiError_BadRequest"
+                    },
+                    {
+                      "$ref": "#/components/schemas/InvalidRequestError"
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        },
+        "description": "Detach any synchronous subagents currently blocking the session and continue them in the background.",
+        "summary": "Background subagents",
+        "x-codeSamples": [
+          {
+            "lang": "js",
+            "source": "import { createOpencodeClient } from \"@opencode-ai/sdk\n\nconst client = createOpencodeClient()\nawait client.experimental.session.background({\n  ...\n})"
+          }
+        ]
+      }
+    },
     "/experimental/resource": {
       "get": {
         "tags": ["experimental"],