diff --git a/README.md b/README.md
index d8552c0..326276f 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,7 @@ craken workspace list
 craken workspace create --name test0
 craken channel send --workspace test0 --channel general hello
 craken dm send --workspace test0 --target orca hello
+craken wiki save --workspace test0 --existing-title Home --content-file ./home.md --base-version 12
 craken workspace tail --workspace test0 --pretty
 craken commands --format text
 craken do workspaces.list
diff --git a/docs/architecture.md b/docs/architecture.md
index 784bbf3..bc33d69 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -4,6 +4,8 @@
 
 The Worker remains the source of truth for product behavior. Dedicated commands call stable API routes directly, while `commands`, `do`, and raw HTTP commands discover and invoke the server-owned `/api/client` catalog so new routes and command syntax are usable before a CLI release is needed.
 
+Wiki saves follow the service's optimistic concurrency contract. Creating a missing page can omit `--base-version`; updating an existing page should read the page first, edit against the returned `latestVersionNumber`, and pass that number as `--base-version`. A stale base version returns the server's 409 conflict payload so scripts can re-read, merge, and retry.
+
 The default help fetches `/api/client` once and renders the server-owned command syntax, descriptions, examples, and operation routes available to the selected bearer session. Authentication and generic transport flags stay local bootstrap behavior; the product command surface belongs to the Worker so API changes do not require a CLI release just to discover or invoke new operations.
 
 The profile file is intentionally compatible with the prior Node CLI:
diff --git a/internal/craken/command_test.go b/internal/craken/command_test.go
index b5b89c7..be19c15 100644
--- a/internal/craken/command_test.go
+++ b/internal/craken/command_test.go
@@ -441,12 +441,12 @@ func TestWikiSaveAndAgentPlanCheck(t *testing.T) {
 		switch r.Method + " " + r.URL.Path {
 		case "GET /api/workspaces":
 			writeJSON(t, w, map[string]any{"workspaces": []map[string]any{{"id": "workspace-id", "name": "test0"}}})
-		case "POST /api/workspaces/workspace-id/wiki/pages":
+		case "PATCH /api/workspaces/workspace-id/wiki/pages/Home":
 			var body map[string]any
 			if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 				t.Fatal(err)
 			}
-			if body["title"] != "Home" || body["content"] != "# Home\n" {
+			if body["title"] != "Home" || body["content"] != "# Home\n" || body["baseVersionNumber"] != float64(12) {
 				t.Fatalf("unexpected wiki body %#v", body)
 			}
 			writeJSON(t, w, map[string]any{"page": body})
@@ -465,7 +465,7 @@ func TestWikiSaveAndAgentPlanCheck(t *testing.T) {
 	}))
 	defer server.Close()
 
-	err := Run(context.Background(), "dev", []string{"wiki", "save", "--token", "test-token", "--base-url", server.URL, "--workspace", "test0", "--title", "Home", "--content-file", contentPath}, strings.NewReader(""), &bytes.Buffer{}, &bytes.Buffer{})
+	err := Run(context.Background(), "dev", []string{"wiki", "save", "--token", "test-token", "--base-url", server.URL, "--workspace", "test0", "--existing-title", "Home", "--title", "Home", "--content-file", contentPath, "--base-version", "12"}, strings.NewReader(""), &bytes.Buffer{}, &bytes.Buffer{})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -478,6 +478,38 @@ func TestWikiSaveAndAgentPlanCheck(t *testing.T) {
 	}
 }
 
+func TestWikiSaveReportsBaseVersionConflict(t *testing.T) {
+	configDir := t.TempDir()
+	t.Setenv("CRAKEN_CONFIG_DIR", configDir)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.Method + " " + r.URL.Path {
+		case "GET /api/workspaces":
+			writeJSON(t, w, map[string]any{"workspaces": []map[string]any{{"id": "workspace-id", "name": "test0"}}})
+		case "PATCH /api/workspaces/workspace-id/wiki/pages/Home":
+			w.WriteHeader(http.StatusConflict)
+			writeJSON(t, w, map[string]any{
+				"conflict": map[string]any{
+					"currentVersionNumber":      13,
+					"receivedBaseVersionNumber": 12,
+					"reason":                    "stale_base_version",
+				},
+				"error": "Wiki page update for \"Home\" conflicted: baseVersionNumber 12 does not match current version 13.",
+			})
+		default:
+			t.Fatalf("unexpected request %s %s", r.Method, r.URL.Path)
+		}
+	}))
+	defer server.Close()
+
+	err := Run(context.Background(), "dev", []string{"wiki", "save", "--token", "test-token", "--base-url", server.URL, "--workspace", "test0", "--existing-title", "Home", "--content", "stale", "--base-version", "12"}, strings.NewReader(""), &bytes.Buffer{}, &bytes.Buffer{})
+	if err == nil {
+		t.Fatal("expected stale wiki save to fail")
+	}
+	if message := err.Error(); !strings.Contains(message, "failed with 409") || !strings.Contains(message, "stale_base_version") {
+		t.Fatalf("expected 409 conflict details, got %q", message)
+	}
+}
+
 func TestFileUploadUsesMultipartAndFolderCreate(t *testing.T) {
 	configDir := t.TempDir()
 	t.Setenv("CRAKEN_CONFIG_DIR", configDir)
diff --git a/internal/craken/util.go b/internal/craken/util.go
index 7bfbd24..b3d03aa 100644
--- a/internal/craken/util.go
+++ b/internal/craken/util.go
@@ -120,6 +120,18 @@ func numberOption(cmd command, name string, fallback int) (int, error) {
 	return parsed, nil
 }
 
+func positiveNumberOption(cmd command, name string) (*int, error) {
+	value := cmd.string(name, "")
+	if value == "" {
+		return nil, nil
+	}
+	parsed, err := strconv.Atoi(value)
+	if err != nil || parsed < 1 {
+		return nil, fmt.Errorf("expected positive integer, got %s", value)
+	}
+	return &parsed, nil
+}
+
 func boolOption(cmd command, name string) bool {
 	return cmd.Flags[name] || cmd.string(name, "") != ""
 }
diff --git a/internal/craken/wiki_agent.go b/internal/craken/wiki_agent.go
index 9be2ae6..f7f4c52 100644
--- a/internal/craken/wiki_agent.go
+++ b/internal/craken/wiki_agent.go
@@ -35,14 +35,25 @@ func runWiki(ctx context.Context, client *client, cmd command, stdout io.Writer)
 		if err != nil {
 			return err
 		}
+		baseVersionNumber, err := positiveNumberOption(cmd, "base-version")
+		if err != nil {
+			return err
+		}
 		if existing := cmd.string("existing-title", ""); existing != "" {
-			return printClientJSON(ctx, client, stdout, "PATCH", wikiPagePath(workspaceID, existing), compact(map[string]any{"content": content, "title": cmd.string("title", existing)}))
+			return printClientJSON(
+				ctx,
+				client,
+				stdout,
+				"PATCH",
+				wikiPagePath(workspaceID, existing),
+				wikiSaveBody(content, cmd.string("title", existing), baseVersionNumber),
+			)
 		}
 		title, err := cmd.required("title")
 		if err != nil {
 			return err
 		}
-		return printClientJSON(ctx, client, stdout, "POST", workspacePath(workspaceID)+"/wiki/pages", map[string]any{"content": content, "title": title})
+		return printClientJSON(ctx, client, stdout, "POST", workspacePath(workspaceID)+"/wiki/pages", wikiSaveBody(content, title, baseVersionNumber))
 	case "delete":
 		title, err := cmd.required("title", "page")
 		if err != nil {
@@ -89,6 +100,14 @@ func runWiki(ctx context.Context, client *client, cmd command, stdout io.Writer)
 	}
 }
 
+func wikiSaveBody(content string, title string, baseVersionNumber *int) map[string]any {
+	body := map[string]any{"content": content, "title": title}
+	if baseVersionNumber != nil {
+		body["baseVersionNumber"] = *baseVersionNumber
+	}
+	return body
+}
+
 func runAgent(ctx context.Context, client *client, cmd command, stdout io.Writer) error {
 	if cmd.Action == "plan-check" {
 		previous, err := jsonOption(cmd, "previous-json", "previous-file", false)