From cbbf64672bb2b0d1fa047d89feef8875d5391df6 Mon Sep 17 00:00:00 2001
From: Guilherme Sehn <guilherme.sehn@therealreal.com>
Date: Wed, 24 Dec 2025 16:49:25 -0300
Subject: [PATCH 1/2] add tests

---
 .../react/src/select/root/SelectRoot.test.tsx | 67 +++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/packages/react/src/select/root/SelectRoot.test.tsx b/packages/react/src/select/root/SelectRoot.test.tsx
index 01d74cd55e0..edca290ddcc 100644
--- a/packages/react/src/select/root/SelectRoot.test.tsx
+++ b/packages/react/src/select/root/SelectRoot.test.tsx
@@ -1488,6 +1488,73 @@ describe('<Select.Root />', () => {
 
         expect(trigger).to.have.attribute('data-filled');
       });
+
+      describe('on multiple selects', () => {
+        it('adds [data-filled] attribute when at least one item is selected', async () => {
+          const { user } = await renderFakeTimers(
+            <Field.Root>
+              <Select.Root multiple>
+                <Select.Trigger data-testid="trigger" />
+                <Select.Portal>
+                  <Select.Positioner>
+                    <Select.Popup>
+                      <Select.Item value="">Select</Select.Item>
+                      <Select.Item value="1">Option 1</Select.Item>
+                      <Select.Item value="2">Option 2</Select.Item>
+                      <Select.Item value="3">Option 3</Select.Item>
+                    </Select.Popup>
+                  </Select.Positioner>
+                </Select.Portal>
+              </Select.Root>
+            </Field.Root>,
+          );
+
+          const trigger = screen.getByTestId('trigger');
+          expect(trigger).not.to.have.attribute('data-filled');
+
+          await user.click(trigger);
+
+          await flushMicrotasks();
+          clock.tick(200);
+
+          const option = screen.getByRole('option', { name: 'Option 1' });
+
+          // Arrow Down to focus the Option 1
+          await user.keyboard('{ArrowDown}');
+          await user.click(option);
+          await flushMicrotasks();
+
+          expect(trigger).to.have.attribute('data-filled', '');
+          await flushMicrotasks();
+
+          const select = screen.getByRole('listbox');
+          expect(select).not.to.have.attribute('data-filled');
+        });
+
+        it('adds [data-filled] attribute when already filled', async () => {
+          await renderFakeTimers(
+            <Field.Root>
+              <Select.Root multiple defaultValue={['1']}>
+                <Select.Trigger data-testid="trigger" />
+                <Select.Portal>
+                  <Select.Positioner>
+                    <Select.Popup>
+                      <Select.Item value="">Select</Select.Item>
+                      <Select.Item value="1">Option 1</Select.Item>
+                      <Select.Item value="2">Option 2</Select.Item>
+                      <Select.Item value="3">Option 3</Select.Item>
+                    </Select.Popup>
+                  </Select.Positioner>
+                </Select.Portal>
+              </Select.Root>
+            </Field.Root>,
+          );
+
+          const trigger = screen.getByTestId('trigger');
+
+          expect(trigger).to.have.attribute('data-filled');
+        });
+      });
     });
 
     it('[data-focused]', async () => {

From 433eef0cc4cffbef16786c71752fd2e889b6cf63 Mon Sep 17 00:00:00 2001
From: Guilherme Sehn <guilherme.sehn@therealreal.com>
Date: Wed, 24 Dec 2025 16:49:31 -0300
Subject: [PATCH 2/2] adjust logic

---
 packages/react/src/select/root/SelectRoot.tsx | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/react/src/select/root/SelectRoot.tsx b/packages/react/src/select/root/SelectRoot.tsx
index f4a0b189ce6..329fe11c2fb 100644
--- a/packages/react/src/select/root/SelectRoot.tsx
+++ b/packages/react/src/select/root/SelectRoot.tsx
@@ -194,8 +194,8 @@ export function SelectRoot<Value, Multiple extends boolean | undefined = false>(
   }, [store, value]);
 
   useIsoLayoutEffect(() => {
-    setFilled(value !== null);
-  }, [value, setFilled]);
+    setFilled(multiple && Array.isArray(value) ? value.length > 0 : value !== null);
+  }, [value, multiple, setFilled]);
 
   useIsoLayoutEffect(
     function syncSelectedIndex() {