diff --git a/acceptance/task_test.go b/acceptance/task_test.go
index f2ad65ce..9b1071ce 100644
--- a/acceptance/task_test.go
+++ b/acceptance/task_test.go
@@ -101,7 +101,7 @@ func TestTaskRunHappyPath(t *testing.T) {
 	params := body["parameters"].(map[string]interface{})
 	assert.Equal(t, params["custom-prompt"], "Fix the flaky test")
 	assert.Equal(t, params["run-pipeline-as-a-tool"], true)
-	assert.Equal(t, params["create-new-branch"], false)
+	assert.Equal(t, params["create-new-branch"], true)
 
 	// Verify auth header
 	assert.Assert(t, runReqs[0].Header.Get("Circle-Token") != "",
@@ -138,7 +138,7 @@ func TestTaskRunBranchOverride(t *testing.T) {
 	assert.Equal(t, body["checkout_branch"], "feature/my-branch")
 }
 
-func TestTaskRunNewBranch(t *testing.T) {
+func TestTaskRunNewBranchFalse(t *testing.T) {
 	cci := fakes.NewFakeCircleCI()
 	srv := httptest.NewServer(cci)
 	defer srv.Close()
@@ -153,7 +153,7 @@ func TestTaskRunNewBranch(t *testing.T) {
 		"task", "run",
 		"--definition", "dev",
 		"--prompt", "Add types",
-		"--new-branch",
+		"--new-branch=false",
 	}, env, workDir)
 
 	assert.Equal(t, result.ExitCode, 0, "stderr: %s", result.Stderr)
@@ -167,7 +167,7 @@ func TestTaskRunNewBranch(t *testing.T) {
 	assert.NilError(t, err)
 
 	params := body["parameters"].(map[string]interface{})
-	assert.Equal(t, params["create-new-branch"], true)
+	assert.Equal(t, params["create-new-branch"], false)
 }
 
 func TestTaskRunPipelineAsToolDefault(t *testing.T) {
diff --git a/docs/CLI.md b/docs/CLI.md
index de24f629..1f3a3e28 100644
--- a/docs/CLI.md
+++ b/docs/CLI.md
@@ -42,7 +42,7 @@ chunk
 │   │   --definition <name|uuid>    # Definition name or UUID (required)
 │   │   --prompt <text>             # Prompt text (required)
 │   │   --branch <branch>           # Branch override
-│   │   --new-branch                # Create a new branch
+│   │   --new-branch                # Create a new branch (default: true; pass =false to commit on checkout branch)
 │   │   --no-pipeline-as-tool       # Disable pipeline-as-tool mode
 │   │   --json                      # Output as JSON
 │   └── config                      # Set up .chunk/run.json for this repository
@@ -146,6 +146,8 @@ chunk
 - `build-prompt` does not write intermediate files by default. Pass `--debug` to write the raw details JSON, analysis markdown, and PR rankings CSV alongside the prompt — useful when diagnosing unexpected prompt output.
 - `task run` defaults to pipeline-as-tool mode; use `--no-pipeline-as-tool`
   to disable.
+- `task run` creates a new branch by default (`create-new-branch: true`);
+  pass `--new-branch=false` to commit on the checkout branch instead.
 - `config set` user keys: `model`. Project keys (`.chunk/config.json`): `orgID`,
   `validation.sidecarImage`. Credentials use `chunk auth set`, not `config set`.
 - **Org ID resolution** for `sidecar create`, `sidecar list`, and other sidecar
diff --git a/internal/cmd/task.go b/internal/cmd/task.go
index 08cd51f2..534fea65 100644
--- a/internal/cmd/task.go
+++ b/internal/cmd/task.go
@@ -92,7 +92,7 @@ func newTaskRunCmd() *cobra.Command {
 	cmd.Flags().StringVar(&definition, "definition", "", "Definition name or UUID")
 	cmd.Flags().StringVar(&prompt, "prompt", "", "Prompt text")
 	cmd.Flags().StringVar(&branch, "branch", "", "Checkout branch override")
-	cmd.Flags().BoolVar(&newBranch, "new-branch", false, "Create a new branch")
+	cmd.Flags().BoolVar(&newBranch, "new-branch", true, "Create a new branch (default true; pass =false to commit on the checkout branch)")
 	cmd.Flags().BoolVar(&noPipelineAsTool, "no-pipeline-as-tool", false, "Disable running pipeline as a tool")
 	cmd.Flags().BoolVar(&jsonOut, "json", false, "Output as JSON")
 
diff --git a/internal/task/task_test.go b/internal/task/task_test.go
index 80511898..fd84be53 100644
--- a/internal/task/task_test.go
+++ b/internal/task/task_test.go
@@ -276,6 +276,7 @@ func TestTriggerRunHappyPath(t *testing.T) {
 		Definition:     "dev",
 		Prompt:         "Fix tests",
 		PipelineAsTool: true,
+		NewBranch:      true,
 	})
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
@@ -324,11 +325,40 @@ func TestTriggerRunHappyPath(t *testing.T) {
 	if params["run-pipeline-as-a-tool"] != true {
 		t.Fatalf("run-pipeline-as-a-tool = %v, want true", params["run-pipeline-as-a-tool"])
 	}
-	if params["create-new-branch"] != false {
-		t.Fatalf("create-new-branch = %v, want false", params["create-new-branch"])
+	if params["create-new-branch"] != true {
+		t.Fatalf("create-new-branch = %v, want true", params["create-new-branch"])
 	}
 }
 
+func TestTriggerRunNoNewBranch(t *testing.T) {
+	cci, client := newFakeAndClient(t)
+	cfg := testCfg()
+
+	_, err := TriggerRun(context.Background(), client, cfg, RunParams{
+		Definition: "dev",
+		Prompt:     "Add feature",
+		NewBranch:  false,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	for _, r := range cci.Recorder.AllRequests() {
+		if r.URL.Path == "/api/v2/agents/org/org-111/project/proj-222/runs" {
+			var body map[string]interface{}
+			if err := json.Unmarshal(r.Body, &body); err != nil {
+				t.Fatalf("unmarshal: %v", err)
+			}
+			params := body["parameters"].(map[string]interface{})
+			if params["create-new-branch"] != false {
+				t.Fatalf("create-new-branch = %v, want false", params["create-new-branch"])
+			}
+			return
+		}
+	}
+	t.Fatal("no request to trigger run endpoint")
+}
+
 func TestTriggerRunBranchOverride(t *testing.T) {
 	cci, client := newFakeAndClient(t)
 	cfg := testCfg()