diff --git a/cmd/volcano/grant_test.go b/cmd/volcano/grant_test.go
index 335a3a5e..67d93812 100644
--- a/cmd/volcano/grant_test.go
+++ b/cmd/volcano/grant_test.go
@@ -170,3 +170,24 @@ func TestGrantIsRefusedOnAccountCommandsBeforeAnyRequest(t *testing.T) {
 		})
 	}
 }
+
+// testFunctionID is the function the invoke tests call.
+const testFunctionID = "99999999-9999-4999-8999-999999999999"
+
+// Invoke sends the grant itself to the data-plane invoke route. It never
+// lists, reads or creates the CLI's service key (runAsWorker fails any
+// /service-keys request). Hosting accepts a grant there from C6 on.
+func TestGrantInvokesWithTheGrantAndNoServiceKey(t *testing.T) {
+	run := runAsWorker(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == http.MethodPost && r.URL.Path == "/functions/"+testFunctionID+"/invoke" {
+			respondExitTestJSON(w, http.StatusOK, `{"ok":true}`)
+			return
+		}
+		respondExitTestJSON(w, http.StatusForbidden, `{"error":"delegated grants cannot be used on this endpoint","code":"grant_route_not_allowed"}`)
+	}, "cloud", "functions", "invoke", "--id", testFunctionID, "--json")
+
+	assert.Equal(t, 0, run.code, run.stderr)
+	assert.Equal(t, []string{"POST /functions/" + testFunctionID + "/invoke"}, run.requests)
+	assert.Equal(t, []string{"Bearer " + testGrant}, run.auth)
+	assert.JSONEq(t, `{"ok":true}`, run.stdout)
+}
diff --git a/internal/cmd/cloud/cloud.go b/internal/cmd/cloud/cloud.go
index 6ec304fd..51d7fe4d 100644
--- a/internal/cmd/cloud/cloud.go
+++ b/internal/cmd/cloud/cloud.go
@@ -65,7 +65,7 @@ func NewResourceCommands(deps cliruntime.Deps) []*cobra.Command {
 		domainscmd.New(deps),
 		durablecmd.New(deps),
 		frontendscmd.New(deps),
-		functionscmd.NewWithOptions(deps, functionscmd.WithInvokeTokenProvider(dataPlaneKeys.ServiceKeyForProject)),
+		functionscmd.NewWithOptions(deps, functionscmd.WithInvokeTokenProvider(dataPlaneKeys.InvokeToken)),
 		lavaflowcmd.New(deps),
 		logscmd.New(deps),
 		notificationscmd.New(deps),
diff --git a/internal/dataplane/service_key.go b/internal/dataplane/service_key.go
index dae659ef..3e3bc6cb 100644
--- a/internal/dataplane/service_key.go
+++ b/internal/dataplane/service_key.go
@@ -10,6 +10,7 @@ import (
 
 	"github.com/Kong/volcano-cli/internal/api"
 	"github.com/Kong/volcano-cli/internal/apiclient"
+	"github.com/Kong/volcano-cli/internal/config"
 	cliruntime "github.com/Kong/volcano-cli/internal/runtime"
 	clisession "github.com/Kong/volcano-cli/internal/session"
 )
@@ -50,6 +51,16 @@ func NewService(deps cliruntime.Deps) Service {
 	}
 }
 
+// InvokeToken returns the bearer for the function invoke route. A pg-
+// delegated grant invokes with itself, as a service key does; any other
+// credential gets the reserved service key, as before.
+func (s Service) InvokeToken(ctx context.Context, project *clisession.ProjectSession) (string, error) {
+	if project != nil && project.Config != nil && config.IsDelegatedGrant(project.Config.Token()) {
+		return strings.TrimSpace(project.Config.Token()), nil
+	}
+	return s.ServiceKeyForProject(ctx, project)
+}
+
 // ServiceKey returns the reserved service key for the current project, creating
 // it when it does not already exist.
 func (s Service) ServiceKey(ctx context.Context) (string, error) {
diff --git a/internal/dataplane/service_key_test.go b/internal/dataplane/service_key_test.go
index 2e86f924..36614fa8 100644
--- a/internal/dataplane/service_key_test.go
+++ b/internal/dataplane/service_key_test.go
@@ -185,3 +185,52 @@ func serviceKeyPayload(id, name, keyValue string) map[string]any {
 		"updated_at":  "2026-05-20T00:00:00Z",
 	}
 }
+
+// A delegated grant invokes with itself. Invoke never lists, reads or creates
+// the reserved service key under a grant, so a grant never causes a
+// long-lived key.
+func TestInvokeTokenUsesADelegatedGrantDirectly(t *testing.T) {
+	setServiceKeyTestHome(t)
+	saveServiceKeyTestConfig(t)
+	t.Setenv("VOLCANO_TOKEN", cliconfig.DelegatedGrantPrefix+"grant-secret")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Errorf("a grant must not reach the API to get an invoke token: %s %s", r.Method, r.URL.Path)
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	service := NewService(cliruntime.Deps{HTTPClient: server.Client(), APIBaseURL: server.URL})
+	project, err := service.sessions.CurrentProject()
+	require.NoError(t, err)
+
+	token, err := service.InvokeToken(t.Context(), project)
+	require.NoError(t, err)
+	assert.Equal(t, cliconfig.DelegatedGrantPrefix+"grant-secret", token)
+}
+
+// Any other credential still gets the reserved service key for invoke.
+func TestInvokeTokenUsesTheServiceKeyForOtherCredentials(t *testing.T) {
+	setServiceKeyTestHome(t)
+	saveServiceKeyTestConfig(t)
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "Bearer platform-token", r.Header.Get("Authorization"))
+		if r.Method == http.MethodGet && r.URL.Path == "/projects/"+testProjectID+"/service-keys" {
+			writeServiceKeyJSON(t, w, http.StatusOK, map[string]any{
+				"data":     []any{serviceKeyPayload("11111111-1111-4111-8111-111111111111", CLIServiceKeyName, "sk-existing")},
+				"has_more": false, "page": 1, "limit": 100, "total": 1,
+			})
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	service := NewService(cliruntime.Deps{HTTPClient: server.Client(), APIBaseURL: server.URL})
+	project, err := service.sessions.CurrentProject()
+	require.NoError(t, err)
+	token, err := service.InvokeToken(t.Context(), project)
+	require.NoError(t, err)
+	assert.Equal(t, "sk-existing", token)
+}