diff --git a/.changeset/silver-lemons-behave.md b/.changeset/silver-lemons-behave.md
new file mode 100644
index 0000000000..39d518f0ba
--- /dev/null
+++ b/.changeset/silver-lemons-behave.md
@@ -0,0 +1,5 @@
+---
+'posthog-js': patch
+---
+
+Fix delayed event flushing after `opt_in_capturing()` (fixes cookieless mode needing reload before events are captured)
diff --git a/packages/browser/src/__tests__/cookieless.test.ts b/packages/browser/src/__tests__/cookieless.test.ts
index bd5ddefc31..92063b98df 100644
--- a/packages/browser/src/__tests__/cookieless.test.ts
+++ b/packages/browser/src/__tests__/cookieless.test.ts
@@ -310,5 +310,32 @@ describe('cookieless', () => {
             expect(beforeSendMock.mock.calls[3][0].properties.$cookieless_mode).toEqual(true)
             expect(posthog.sessionRecording).toBeFalsy()
         })
+
+        it('should restart autocapture after opt_in_capturing in cookieless mode', async () => {
+            const { posthog } = await setup({
+                cookieless_mode: 'on_reject',
+            })
+
+            // Mock the autocapture startIfEnabled method
+            const mockStartIfEnabled = jest.fn()
+            const originalStartIfEnabled = posthog.autocapture?.startIfEnabled
+            if (posthog.autocapture) {
+                posthog.autocapture.startIfEnabled = mockStartIfEnabled
+            }
+
+            // Clear any previous startIfEnabled calls
+            mockStartIfEnabled.mockClear()
+
+            // Opt in
+            posthog.opt_in_capturing()
+
+            // Autocapture should be restarted immediately after opt-in
+            expect(mockStartIfEnabled).toHaveBeenCalledTimes(1)
+
+            // Restore original method
+            if (posthog.autocapture && originalStartIfEnabled) {
+                posthog.autocapture.startIfEnabled = originalStartIfEnabled
+            }
+        })
     })
 })
diff --git a/packages/browser/src/posthog-core.ts b/packages/browser/src/posthog-core.ts
index 72cabc87ba..21b5cbc8b1 100644
--- a/packages/browser/src/posthog-core.ts
+++ b/packages/browser/src/posthog-core.ts
@@ -2925,6 +2925,9 @@ export class PostHog {
             this.surveys.loadIfEnabled()
         }
 
+        // Restart autocapture after opting in
+        this.autocapture?.startIfEnabled()
+
         // Don't capture if captureEventName is null or false
         if (isUndefined(options?.captureEventName) || options?.captureEventName) {
             this.capture(options?.captureEventName ?? '$opt_in', options?.captureProperties, { send_instantly: true })