diff --git a/docs/changelog/118958.yaml b/docs/changelog/118958.yaml
new file mode 100644
index 0000000000000..fb0fd6388ab61
--- /dev/null
+++ b/docs/changelog/118958.yaml
@@ -0,0 +1,5 @@
+pr: 118958
+summary: Add missing timeouts to rest-api-spec SLM APIs
+area: ILM+SLM
+type: bug
+issues: []
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.delete_lifecycle.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.delete_lifecycle.json
index 12202a7a2a7b1..1d66312f053c7 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.delete_lifecycle.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.delete_lifecycle.json
@@ -25,6 +25,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_lifecycle.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_lifecycle.json
index 1395a3d3275ae..71f1727a8638b 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_lifecycle.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_lifecycle.json
@@ -25,6 +25,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_retention.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_retention.json
index f6ce3e75cc379..4166122d5bf1d 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_retention.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.execute_retention.json
@@ -19,6 +19,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_lifecycle.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_lifecycle.json
index 94d0772a405da..406fee6015522 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_lifecycle.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_lifecycle.json
@@ -31,6 +31,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_stats.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_stats.json
index aa693ad31711c..05281ff46cb8d 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_stats.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_stats.json
@@ -19,6 +19,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_status.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_status.json
index 92ba1b4c321e6..404f92f55921f 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_status.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.get_status.json
@@ -19,6 +19,15 @@
         }
       ]
     },
-    "params":{}
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    }
   }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.put_lifecycle.json b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.put_lifecycle.json
index 7e7babb987c79..621ed870ffdbe 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/slm.put_lifecycle.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/slm.put_lifecycle.json
@@ -26,7 +26,16 @@
         }
       ]
     },
-    "params":{},
+    "params":{
+      "master_timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout for connection to master node"
+      },
+      "timeout":{
+        "type":"time",
+        "description":"Explicit operation timeout"
+      }
+    },
     "body":{
       "description":"The snapshot lifecycle policy definition to register"
     }