diff --git a/backend/internal/cli/session.go b/backend/internal/cli/session.go
index cae02f0cb5..b46c07e456 100644
--- a/backend/internal/cli/session.go
+++ b/backend/internal/cli/session.go
@@ -36,10 +36,20 @@ type sessionClaimPROptions struct {
 	noTakeover bool
 }
 
+type sessionMergePolicyOptions struct {
+	project            string
+	json               bool
+	terminateOnPRMerge bool
+}
+
 type sessionRenameRequest struct {
 	DisplayName string `json:"displayName"`
 }
 
+type sessionMergePolicyRequest struct {
+	TerminateOnPRMerge bool `json:"terminateOnPrMerge"`
+}
+
 type sessionDTO struct {
 	ID           string          `json:"id"`
 	ProjectID    string          `json:"projectId"`
@@ -82,6 +92,13 @@ type renameSessionResponse struct {
 	DisplayName string `json:"displayName"`
 }
 
+type setMergePolicyResponse struct {
+	OK                 bool       `json:"ok"`
+	SessionID          string     `json:"sessionId"`
+	TerminateOnPRMerge bool       `json:"terminateOnPrMerge"`
+	Session            sessionDTO `json:"session"`
+}
+
 type cleanupSkippedSession struct {
 	SessionID string `json:"sessionId"`
 	Reason    string `json:"reason"`
@@ -146,6 +163,7 @@ func newSessionCommand(ctx *commandContext) *cobra.Command {
 	cmd.AddCommand(newSessionKillCommand(ctx))
 	cmd.AddCommand(newSessionRestoreCommand(ctx))
 	cmd.AddCommand(newSessionRenameCommand(ctx))
+	cmd.AddCommand(newSessionSetMergePolicyCommand(ctx))
 	cmd.AddCommand(newSessionCleanupCommand(ctx))
 	cmd.AddCommand(newSessionClaimPRCommand(ctx))
 	return cmd
@@ -243,6 +261,30 @@ func newSessionRenameCommand(ctx *commandContext) *cobra.Command {
 	return cmd
 }
 
+func newSessionSetMergePolicyCommand(ctx *commandContext) *cobra.Command {
+	var opts sessionMergePolicyOptions
+	cmd := &cobra.Command{
+		Use:   "set-merge-policy <id>",
+		Short: "Set whether the session auto-terminates when its PR merges",
+		Args:  oneSessionIDArg,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if !cmd.Flags().Changed("terminate-on-pr-merge") {
+				return usageError{errors.New("--terminate-on-pr-merge is required (true or false)")}
+			}
+			id, err := normalizeSessionID(args[0])
+			if err != nil {
+				return err
+			}
+			return ctx.setSessionMergePolicy(cmd.Context(), cmd, id, opts)
+		},
+	}
+	f := cmd.Flags()
+	addSessionProjectFlag(f, &opts.project, "Project id to scope the lookup")
+	f.BoolVar(&opts.terminateOnPRMerge, "terminate-on-pr-merge", false, "Terminate the session when its claimed PR merges (required)")
+	f.BoolVar(&opts.json, "json", false, "Output as JSON")
+	return cmd
+}
+
 func newSessionCleanupCommand(ctx *commandContext) *cobra.Command {
 	var opts sessionCleanupOptions
 	cmd := &cobra.Command{
@@ -494,6 +536,32 @@ func (c *commandContext) renameSession(ctx context.Context, cmd *cobra.Command,
 	return err
 }
 
+func (c *commandContext) setSessionMergePolicy(ctx context.Context, cmd *cobra.Command, id string, opts sessionMergePolicyOptions) error {
+	if opts.project != "" {
+		if _, err := c.fetchScopedSession(ctx, id, opts.project); err != nil {
+			return err
+		}
+	}
+	var res setMergePolicyResponse
+	req := sessionMergePolicyRequest{TerminateOnPRMerge: opts.terminateOnPRMerge}
+	if err := c.patchJSON(ctx, "sessions/"+url.PathEscape(id)+"/merge-policy", req, &res); err != nil {
+		return err
+	}
+	if opts.json {
+		return writeJSON(cmd.OutOrStdout(), res)
+	}
+	sessionID := res.SessionID
+	if sessionID == "" {
+		sessionID = id
+	}
+	policy := "keep session after PR merge"
+	if res.TerminateOnPRMerge {
+		policy = "terminate session when PR merges"
+	}
+	_, err := fmt.Fprintf(cmd.OutOrStdout(), "session %s merge policy: %s\n", sessionID, policy)
+	return err
+}
+
 func (c *commandContext) cleanupSessions(ctx context.Context, cmd *cobra.Command, opts sessionCleanupOptions) error {
 	candidates, err := c.previewCleanupSessions(ctx, opts.project)
 	if err != nil {
diff --git a/backend/internal/cli/session_test.go b/backend/internal/cli/session_test.go
index 6b3ba04b0a..c9bddfb1c3 100644
--- a/backend/internal/cli/session_test.go
+++ b/backend/internal/cli/session_test.go
@@ -3,6 +3,7 @@ package cli
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -95,6 +96,13 @@ func sessionCommandServer(t *testing.T) (*httptest.Server, *sessionRequestLog) {
 				return
 			}
 			_, _ = io.WriteString(w, `{"ok":true,"sessionId":"demo-1","displayName":`+jsonQuote(req.DisplayName)+`}`)
+		case r.Method == http.MethodPatch && r.URL.Path == "/api/v1/sessions/demo-1/merge-policy":
+			var req sessionMergePolicyRequest
+			if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+				http.Error(w, err.Error(), http.StatusBadRequest)
+				return
+			}
+			_, _ = io.WriteString(w, `{"ok":true,"sessionId":"demo-1","terminateOnPrMerge":`+fmt.Sprintf("%t", req.TerminateOnPRMerge)+`,"session":`+sessionJSON("demo-1", "demo", "worker", "working", false)+`}`)
 		default:
 			http.NotFound(w, r)
 		}
@@ -432,9 +440,60 @@ func TestSessionRename_SuccessWithProjectScope(t *testing.T) {
 	}
 }
 
+func TestSessionSetMergePolicy_Success(t *testing.T) {
+	cfg := setConfigEnv(t)
+	srv, log := sessionCommandServer(t)
+	writeRunFileFor(t, cfg, srv)
+
+	out, errOut, err := executeCLI(t, Deps{
+		ProcessAlive: func(int) bool { return true },
+	}, "session", "set-merge-policy", "demo-1", "--terminate-on-pr-merge", "-p", "demo")
+	if err != nil {
+		t.Fatalf("session set-merge-policy failed: %v\nstderr=%s", err, errOut)
+	}
+	if !strings.Contains(out, "session demo-1 merge policy: terminate session when PR merges") {
+		t.Fatalf("unexpected set-merge-policy output:\n%s", out)
+	}
+	want := []string{"GET /api/v1/sessions/demo-1", "PATCH /api/v1/sessions/demo-1/merge-policy"}
+	if got := log.all(); !reflect.DeepEqual(got, want) {
+		t.Fatalf("requests = %#v, want %#v", got, want)
+	}
+}
+
+func TestSessionSetMergePolicy_DisableAndJSON(t *testing.T) {
+	cfg := setConfigEnv(t)
+	srv, _ := sessionCommandServer(t)
+	writeRunFileFor(t, cfg, srv)
+
+	out, errOut, err := executeCLI(t, Deps{
+		ProcessAlive: func(int) bool { return true },
+	}, "session", "set-merge-policy", "demo-1", "--terminate-on-pr-merge=false", "--json")
+	if err != nil {
+		t.Fatalf("session set-merge-policy --json failed: %v\nstderr=%s", err, errOut)
+	}
+	var got setMergePolicyResponse
+	if err := json.Unmarshal([]byte(out), &got); err != nil {
+		t.Fatalf("set-merge-policy --json output is not decodable: %v\noutput=%s", err, out)
+	}
+	if !got.OK || got.SessionID != "demo-1" || got.TerminateOnPRMerge {
+		t.Fatalf("unexpected merge policy JSON: %#v", got)
+	}
+}
+
+func TestSessionSetMergePolicy_MissingFlagIsUsageError(t *testing.T) {
+	setConfigEnv(t)
+	_, errOut, err := executeCLI(t, Deps{}, "session", "set-merge-policy", "demo-1")
+	if err == nil {
+		t.Fatal("expected missing --terminate-on-pr-merge to fail")
+	}
+	if got := ExitCode(err); got != 2 {
+		t.Fatalf("exit code = %d, want 2 (err=%v stderr=%s)", got, err, errOut)
+	}
+}
+
 func TestSessionCommands_MissingIDIsUsageError(t *testing.T) {
 	setConfigEnv(t)
-	for _, sub := range []string{"get", "kill", "restore"} {
+	for _, sub := range []string{"get", "kill", "restore", "set-merge-policy"} {
 		t.Run(sub, func(t *testing.T) {
 			_, _, err := executeCLI(t, Deps{}, "session", sub)
 			if err == nil {
diff --git a/docs/cli/README.md b/docs/cli/README.md
index 3302f0f941..583a2ff8da 100644
--- a/docs/cli/README.md
+++ b/docs/cli/README.md
@@ -51,6 +51,7 @@ Every product command resolves to a daemon HTTP route. Run `ao <command>
 | `ao session kill <id>`              | `POST /api/v1/sessions/{id}/kill`              |
 | `ao session restore <id>`           | `POST /api/v1/sessions/{id}/restore`           |
 | `ao session rename <id> <name>`     | `PATCH /api/v1/sessions/{id}`                  |
+| `ao session set-merge-policy <id>`  | `PATCH /api/v1/sessions/{id}/merge-policy`     |
 | `ao session cleanup`                | `POST /api/v1/sessions/cleanup`                |
 | `ao session claim-pr <id> <pr-ref>` | `POST /api/v1/sessions/{id}/pr/claim`          |
 | `ao orchestrator ls`                | `GET /api/v1/orchestrators`                    |