diff --git a/crates/workspace/src/multi_workspace_tests.rs b/crates/workspace/src/multi_workspace_tests.rs
index 9cab28c0ca4ab34b2189985e898285dd82dd4f32..5f15f6422dd584234db89f8986d6c0eb5c32d635 100644
--- a/crates/workspace/src/multi_workspace_tests.rs
+++ b/crates/workspace/src/multi_workspace_tests.rs
@@ -1,9 +1,12 @@
+use std::path::PathBuf;
+
 use super::*;
 use fs::FakeFs;
 use gpui::TestAppContext;
 use project::{DisableAiSettings, ProjectGroupKey};
 use serde_json::json;
 use settings::SettingsStore;
+use util::path;
 
 fn init_test(cx: &mut TestAppContext) {
     cx.update(|cx| {
@@ -152,6 +155,51 @@ async fn test_project_group_keys_add_workspace(cx: &mut TestAppContext) {
     });
 }
 
+#[gpui::test]
+async fn test_open_new_window_does_not_open_sidebar_on_existing_window(cx: &mut TestAppContext) {
+    init_test(cx);
+
+    let app_state = cx.update(AppState::test);
+    let fs = app_state.fs.as_fake();
+    fs.insert_tree(path!("/project_a"), json!({ "file.txt": "" }))
+        .await;
+    fs.insert_tree(path!("/project_b"), json!({ "file.txt": "" }))
+        .await;
+
+    let project = Project::test(app_state.fs.clone(), [path!("/project_a").as_ref()], cx).await;
+
+    let window = cx.add_window(|window, cx| MultiWorkspace::test_new(project, window, cx));
+
+    window
+        .read_with(cx, |mw, _cx| {
+            assert!(!mw.sidebar_open(), "sidebar should start closed",);
+        })
+        .unwrap();
+
+    cx.update(|cx| {
+        open_paths(
+            &[PathBuf::from(path!("/project_b"))],
+            app_state,
+            OpenOptions {
+                open_mode: OpenMode::NewWindow,
+                ..OpenOptions::default()
+            },
+            cx,
+        )
+    })
+    .await
+    .unwrap();
+
+    window
+        .read_with(cx, |mw, _cx| {
+            assert!(
+                !mw.sidebar_open(),
+                "opening a project in a new window must not open the sidebar on the original window",
+            );
+        })
+        .unwrap();
+}
+
 #[gpui::test]
 async fn test_project_group_keys_duplicate_not_added(cx: &mut TestAppContext) {
     init_test(cx);
diff --git a/crates/workspace/src/workspace.rs b/crates/workspace/src/workspace.rs
index f9330f07ee3d057f33aa660fd491d2e61642d658..b7fa93b2945630b2e691579a7111dedee745b0e6 100644
--- a/crates/workspace/src/workspace.rs
+++ b/crates/workspace/src/workspace.rs
@@ -9329,6 +9329,12 @@ pub struct OpenOptions {
     pub open_in_dev_container: bool,
 }
 
+impl OpenOptions {
+    fn should_reuse_existing_window(&self) -> bool {
+        self.open_new_workspace.is_none() && self.open_mode != OpenMode::NewWindow
+    }
+}
+
 /// The result of opening a workspace via [`open_paths`], [`Workspace::new_local`],
 /// or [`Workspace::open_workspace_for_paths`].
 pub struct OpenResult {
@@ -9476,7 +9482,7 @@ pub fn open_paths(
 
         // Fallback: if no workspace contains the paths and all paths are files,
         // prefer an existing local workspace window (active window first).
-        if open_options.open_new_workspace.is_none() && existing.is_none() {
+        if open_options.should_reuse_existing_window() && existing.is_none() {
             let all_paths = abs_paths.iter().map(|path| app_state.fs.metadata(path));
             let all_metadatas = futures::future::join_all(all_paths)
                 .await
@@ -9509,7 +9515,7 @@ pub fn open_paths(
         // workspace matched, check the user's setting to decide whether to add
         // the directory as a new workspace in the active window's MultiWorkspace
         // or open a new window.
-        if open_options.open_new_workspace.is_none() && existing.is_none() {
+        if open_options.should_reuse_existing_window() && existing.is_none() {
             let use_existing_window = open_options.force_existing_window
                 || cx.update(|cx| {
                     WorkspaceSettings::get_global(cx).cli_default_open_behavior