diff --git a/changelog.d/fixes/12647-background-degradation-deletions.md b/changelog.d/fixes/12647-background-degradation-deletions.md
new file mode 100644
index 0000000000..5339d07594
--- /dev/null
+++ b/changelog.d/fixes/12647-background-degradation-deletions.md
@@ -0,0 +1 @@
+- **fix(config):** Persist deletions of built-in background-degradation entries — when a stored settings record exists its `degradationMap` is now authoritative instead of being merged under the defaults, so an entry the user removed in the dashboard no longer reappears on the next apply or restart ([#12424](https://github.com/diegosouzapw/OmniRoute/issues/12424))
diff --git a/src/lib/config/runtimeSettings.ts b/src/lib/config/runtimeSettings.ts
index 0cb93c8fee..ed5930cbb7 100644
--- a/src/lib/config/runtimeSettings.ts
+++ b/src/lib/config/runtimeSettings.ts
@@ -323,10 +323,11 @@ async function applyBackgroundDegradationSection(backgroundDegradation: JsonReco
 
   setBackgroundDegradationConfig({
     enabled: backgroundDegradation.enabled === true,
-    degradationMap: {
-      ...getDefaultDegradationMap(),
-      ...normalizeStringRecord(backgroundDegradation.degradationMap),
-    },
+    // #12424: a present stored record is authoritative for degradationMap — do NOT back-fill
+    // defaults, or a key the user deleted (absent from the stored map) resurrects on every
+    // apply/restart. Mirrors detectionPatterns below, which already treats a present stored
+    // value as authoritative and only falls back to defaults when it is empty.
+    degradationMap: normalizeStringRecord(backgroundDegradation.degradationMap),
     detectionPatterns:
       normalizeStringArray(backgroundDegradation.detectionPatterns).length > 0
         ? normalizeStringArray(backgroundDegradation.detectionPatterns)
diff --git a/tests/unit/settings/background-degradation-deletions-12424.test.ts b/tests/unit/settings/background-degradation-deletions-12424.test.ts
new file mode 100644
index 0000000000..f5b157a723
--- /dev/null
+++ b/tests/unit/settings/background-degradation-deletions-12424.test.ts
@@ -0,0 +1,57 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+process.env.DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-bgdeg-12424-"));
+
+const { applyRuntimeSettings, resetRuntimeSettingsStateForTests } = await import(
+  "../../../src/lib/config/runtimeSettings.ts"
+);
+const {
+  getBackgroundDegradationConfig,
+  getDefaultDegradationMap,
+  getDefaultDetectionPatterns,
+  setBackgroundDegradationConfig,
+} = await import("../../../open-sse/services/backgroundTaskDetector.ts");
+
+// Issue #12424: deleting a built-in background-degradation entry through the dashboard
+// did not persist — the runtime loader merged defaults *under* the stored map, so a key
+// the user removed (absent from the stored record) was indistinguishable from one never
+// touched and always came back on the next apply/restart.
+test("stored degradationMap that omits a default key does not resurrect it (#12424)", async () => {
+  resetRuntimeSettingsStateForTests();
+  setBackgroundDegradationConfig({
+    enabled: false,
+    degradationMap: getDefaultDegradationMap(),
+    detectionPatterns: getDefaultDetectionPatterns(),
+  });
+
+  const defaults = getDefaultDegradationMap();
+  const deletedKey = "gpt-5";
+  const keptKey = "gpt-4o";
+  assert.ok(
+    defaults[deletedKey] && defaults[keptKey],
+    "fixture assumes these default keys exist in DEFAULT_DEGRADATION_MAP"
+  );
+
+  // The stored map is every default except the one the user deleted.
+  const stored: Record<string, string> = { ...defaults };
+  delete stored[deletedKey];
+
+  await applyRuntimeSettings(
+    { backgroundDegradation: JSON.stringify({ enabled: true, degradationMap: stored }) },
+    { force: true, source: "test" }
+  );
+
+  const applied = getBackgroundDegradationConfig().degradationMap;
+
+  // The entries the user kept still apply…
+  assert.equal(applied[keptKey], defaults[keptKey], "a kept default entry still applies");
+  // …and the one they deleted stays deleted instead of being back-filled from defaults.
+  assert.ok(
+    !(deletedKey in applied),
+    `deleted default '${deletedKey}' must not be re-added from defaults`
+  );
+});