diff --git a/packages/shared/pkg/featureflags/client.go b/packages/shared/pkg/featureflags/client.go
index d4dd591c6c..7722228808 100644
--- a/packages/shared/pkg/featureflags/client.go
+++ b/packages/shared/pkg/featureflags/client.go
@@ -159,6 +159,10 @@ func NewClientWithLogLevel(deploymentEnvironment, serviceName, serviceVersion st
 		return nil, firecrackerVersionsEnvErr
 	}
 
+	if extraCompatibleNodeModelsEnvErr != nil {
+		return nil, extraCompatibleNodeModelsEnvErr
+	}
+
 	cfg := ldclient.Config{
 		ApplicationInfo:  applicationInfo(deploymentEnvironment, serviceName, serviceVersion),
 		Logging:          ldcomponents.Logging().MinLevel(logLevel),
@@ -412,4 +416,4 @@ func (c *Client) allContexts(ctx context.Context, contexts []ldcontext.Context)
 	}
 
 	return append(all, contexts...)
-}
+}
\ No newline at end of file
diff --git a/packages/shared/pkg/featureflags/flags.go b/packages/shared/pkg/featureflags/flags.go
index 592bd2e195..9ae0a20839 100644
--- a/packages/shared/pkg/featureflags/flags.go
+++ b/packages/shared/pkg/featureflags/flags.go
@@ -1182,6 +1182,32 @@ func FirecrackerVersionsFallback(base map[string]string, raw string) (map[string
 // A malformed override keeps the baked map here and fails NewClient, so the service stops with the message instead of a package-init panic.
 var firecrackerVersionsFallback, firecrackerVersionsEnvErr = FirecrackerVersionsFallback(FirecrackerVersionMap, env.GetEnv(FirecrackerVersionsEnv, ""))
 
+// ExtraCompatibleNodeModelsEnv overrides the extra-compatible-node-models fallback where
+// there is no LaunchDarkly: a JSON object of build CPU model to the node CPU models that
+// build may run on, e.g. {"106":["173"]}. Pairs are one-way and architecture and family
+// must still match at placement; this only decides where the value comes from, not the rule.
+// LaunchDarkly, where present, still overrides it.
+const ExtraCompatibleNodeModelsEnv = "EXTRA_COMPATIBLE_NODE_MODELS"
+
+// parseExtraCompatibleNodeModels turns the ExtraCompatibleNodeModelsEnv raw value into the
+// flag fallback. Empty is null (no extra pairs). A malformed value fails NewClient via
+// extraCompatibleNodeModelsEnvErr, like FirecrackerVersions, so the service stops with the
+// message instead of silently placing on the base compatibility rule.
+func parseExtraCompatibleNodeModels(raw string) (ldvalue.Value, error) {
+	if strings.TrimSpace(raw) == "" {
+		return ldvalue.Null(), nil
+	}
+
+	var m map[string][]string
+	if err := json.Unmarshal([]byte(raw), &m); err != nil {
+		return ldvalue.Null(), fmt.Errorf("%s: expected a JSON object of build model to node models: %w", ExtraCompatibleNodeModelsEnv, err)
+	}
+
+	return ldvalue.FromJSONMarshal(m), nil
+}
+
+var extraCompatibleNodeModelsValue, extraCompatibleNodeModelsEnvErr = parseExtraCompatibleNodeModels(env.GetEnv(ExtraCompatibleNodeModelsEnv, ""))
+
 // BuildIoEngine Sync is used by default as there seems to be a bad interaction between Async and a lot of io operations.
 var (
 	BuildFirecrackerVersion = NewStringFlag("build-firecracker-version", env.GetEnv("DEFAULT_FIRECRACKER_VERSION", DefaultFirecrackerVersion))
@@ -1311,7 +1337,7 @@ var (
 	//
 	// Null (the default) or a malformed value adds nothing. It applies to every
 	// placement, and FsOnlyResumeCPUModelFlag still narrows on top of it.
-	ExtraCompatibleNodeModelsFlag = NewJSONFlag("extra-compatible-node-models", ldvalue.Null())
+	ExtraCompatibleNodeModelsFlag = NewJSONFlag("extra-compatible-node-models", extraCompatibleNodeModelsValue)
 
 	DefaultPersistentVolumeType = NewStringFlag("default-persistent-volume-type", "")
 	BuildNodeInfo               = NewJSONFlag("preferred-build-node", ldvalue.Null())
@@ -1828,4 +1854,4 @@ func GetExtraCompatibleNodeModels(ctx context.Context, ff *Client, contexts ...l
 	}
 
 	return extra
-}
+}
\ No newline at end of file
diff --git a/packages/shared/pkg/featureflags/flags_test.go b/packages/shared/pkg/featureflags/flags_test.go
index e792bfab9c..b3e930a53a 100644
--- a/packages/shared/pkg/featureflags/flags_test.go
+++ b/packages/shared/pkg/featureflags/flags_test.go
@@ -498,3 +498,43 @@ func TestResolveFirecrackerVersion_OverriddenLineServesNewRelease(t *testing.T)
 	assert.Equal(t, "v1.14-0.3.1", ResolveFirecrackerVersion(t.Context(), client, "v1.14-0.3.1"))
 	assert.Equal(t, "v1.14.1_431f1fc", ResolveFirecrackerVersion(t.Context(), client, "v1.14.1_431f1fc"))
 }
+
+func TestParseExtraCompatibleNodeModels(t *testing.T) {
+	t.Parallel()
+
+	t.Run("empty is null without error", func(t *testing.T) {
+		t.Parallel()
+		v, err := parseExtraCompatibleNodeModels("")
+		require.NoError(t, err)
+		assert.True(t, v.IsNull())
+	})
+
+	t.Run("whitespace is null without error", func(t *testing.T) {
+		t.Parallel()
+		v, err := parseExtraCompatibleNodeModels("  \n ")
+		require.NoError(t, err)
+		assert.True(t, v.IsNull())
+	})
+
+	t.Run("object parses to the flag value", func(t *testing.T) {
+		t.Parallel()
+		v, err := parseExtraCompatibleNodeModels(`{"106":["173"]}`)
+		require.NoError(t, err)
+
+		td := ldtestdata.DataSource()
+		td.Update(td.Flag(ExtraCompatibleNodeModelsFlag.Key()).ValueForAll(v))
+		client, err := NewClientWithDatasource(td)
+		require.NoError(t, err)
+		t.Cleanup(func() { require.NoError(t, client.Close(context.WithoutCancel(t.Context()))) })
+
+		assert.Equal(t, map[string][]string{"106": {"173"}}, GetExtraCompatibleNodeModels(t.Context(), client))
+	})
+
+	t.Run("malformed JSON errors and is null", func(t *testing.T) {
+		t.Parallel()
+		v, err := parseExtraCompatibleNodeModels(`{"106":`)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), ExtraCompatibleNodeModelsEnv)
+		assert.True(t, v.IsNull())
+	})
+}
\ No newline at end of file