diff --git a/.prettierignore b/.prettierignore
index f2ddf012c98e..f616ea97e557 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,2 +1,3 @@
 *.md
 .nxcache
+packages/browser-integration-tests/fixtures/loader.js
diff --git a/packages/browser-integration-tests/.eslintrc.js b/packages/browser-integration-tests/.eslintrc.js
index 47e485f9068a..a19cfba8812a 100644
--- a/packages/browser-integration-tests/.eslintrc.js
+++ b/packages/browser-integration-tests/.eslintrc.js
@@ -13,6 +13,14 @@ module.exports = {
     'fixtures/**',
     'tmp/**',
   ],
+  overrides: [
+    {
+      files: ['loader-suites/**/{subject,init}.js'],
+      globals: {
+        Sentry: true,
+      },
+    },
+  ],
   parserOptions: {
     sourceType: 'module',
   },
diff --git a/packages/browser-integration-tests/fixtures/loader.js b/packages/browser-integration-tests/fixtures/loader.js
index 5ae0a94ebda8..a6fa24465a4f 100644
--- a/packages/browser-integration-tests/fixtures/loader.js
+++ b/packages/browser-integration-tests/fixtures/loader.js
@@ -1,4 +1,4 @@
-!function(e,n,r,t,i,o,a,c,s){for(var f=s,forceLoad=!1,u=0;u<document.scripts.length;u++)if(document.scripts[u].src.indexOf(o)>-1){f&&"no"===document.scripts[u].getAttribute("data-lazy")&&(f=!1);break}var p=!1,d=[],l=function(e){("e"in e||"p"in e||e.f&&e.f.indexOf("capture")>-1||e.f&&e.f.indexOf("showReportDialog")>-1)&&f&&h(d),l.data.push(e)};function _(){l({e:[].slice.call(arguments)})}function v(e){l({p:"reason"in e?e.reason:"detail"in e&&"reason"in e.detail?e.detail.reason:e})}function h(o){if(!p){p=!0;var s=n.scripts[0],f=n.createElement("script");f.src=a,f.crossOrigin="anonymous",f.addEventListener("load",(function(){try{e.removeEventListener(r,_),e.removeEventListener(t,v),e.SENTRY_SDK_SOURCE="loader";var n=e[i],a=n.init;n.init=function(e){var r=c;for(var t in e)Object.prototype.hasOwnProperty.call(e,t)&&(r[t]=e[t]);!function(e,n){var r=e.integrations||[];if(!Array.isArray(r))return;var t=r.map((function(e){return e.name}));e.tracesSampleRate&&-1===t.indexOf("BrowserTracing")&&r.push(new n.BrowserTracing);(e.replaysSessionSampleRate||e.replaysOnErrorSampleRate)&&-1===t.indexOf("Replay")&&r.push(new n.Replay);e.integrations=r}(r,n),a(r)},function(n,r){try{for(var t=0;t<n.length;t++)"function"==typeof n[t]&&n[t]();var i=l.data,o=!(void 0===(u=e.__SENTRY__)||!u.hub||!u.hub.getClient());i.sort((function(e){return"init"===e.f?-1:0}));var a=!1;for(t=0;t<i.length;t++)if(i[t].f){a=!0;var c=i[t];!1===o&&"init"!==c.f&&r.init(),o=!0,r[c.f].apply(r,c.a)}!1===o&&!1===a&&r.init();var s=e.onerror,f=e.onunhandledrejection;for(t=0;t<i.length;t++)"e"in i[t]&&s?s.apply(e,i[t].e):"p"in i[t]&&f&&f.apply(e,[i[t].p])}catch(e){console.error(e)}var u}(o,n)}catch(e){console.error(e)}})),s.parentNode.insertBefore(f,s)}}l.data=[],e[i]=e[i]||{},e[i].onLoad=function(e){d.push(e),f&&!forceLoad||h(d)},e[i].forceLoad=function(){forceLoad=!0,f&&setTimeout((function(){h(d)}))},["init","addBreadcrumb","captureMessage","captureException","captureEvent","configureScope","withScope","showReportDialog"].forEach((function(n){e[i][n]=function(){l({f:n,a:arguments})}})),e.addEventListener(r,_),e.addEventListener(t,v),f||setTimeout((function(){h(d)}))}
+!function(n,e,r,t,i,o,a,c,u){for(var s=u,f=0;f<document.scripts.length;f++)if(document.scripts[f].src.indexOf(o)>-1){s&&"no"===document.scripts[f].getAttribute("data-lazy")&&(s=!1);break}var p=[];function l(n){return"e"in n}function d(n){return"p"in n}function _(n){return"f"in n}var v=[];function h(n){s&&(l(n)||d(n)||_(n)&&n.f.indexOf("capture")>-1||_(n)&&n.f.indexOf("showReportDialog")>-1)&&O(),v.push(n)}function y(){h({e:[].slice.call(arguments)})}function E(n){h({p:"reason"in n?n.reason:"detail"in n&&"reason"in n.detail?n.detail.reason:n})}function m(){try{n.SENTRY_SDK_SOURCE="loader";var e=n[i],o=e.init;e.init=function(i){n.removeEventListener(r,y),n.removeEventListener(t,E);var a=c;for(var u in i)Object.prototype.hasOwnProperty.call(i,u)&&(a[u]=i[u]);!function(n,e){var r=n.integrations||[];if(!Array.isArray(r))return;var t=r.map((function(n){return n.name}));n.tracesSampleRate&&-1===t.indexOf("BrowserTracing")&&r.push(new e.BrowserTracing);(n.replaysSessionSampleRate||n.replaysOnErrorSampleRate)&&-1===t.indexOf("Replay")&&r.push(new e.Replay);n.integrations=r}(a,e),o(a)},setTimeout((function(){return function(e){try{for(var r=0;r<p.length;r++)"function"==typeof p[r]&&p[r]();for(r=0;r<v.length;r++){_(o=v[r])&&"init"===o.f&&e.init.apply(e,o.a)}R()||e.init();var t=n.onerror,i=n.onunhandledrejection;for(r=0;r<v.length;r++){var o;if(_(o=v[r])){if("init"===o.f)continue;e[o.f].apply(e,o.a)}else l(o)&&t?t.apply(n,o.e):d(o)&&i&&i.apply(n,[o.p])}}catch(n){console.error(n)}}(e)}))}catch(n){console.error(n)}}var g=!1;function O(){if(!g){g=!0;var n=e.scripts[0],r=e.createElement("script");r.src=a,r.crossOrigin="anonymous",r.addEventListener("load",m,{once:!0,passive:!0}),n.parentNode.insertBefore(r,n)}}function R(){var e=n.__SENTRY__;return!(void 0===e||!e.hub||!e.hub.getClient())}n[i]=n[i]||{},n[i].onLoad=function(n){R()?n():p.push(n)},n[i].forceLoad=function(){setTimeout((function(){O()}))},["init","addBreadcrumb","captureMessage","captureException","captureEvent","configureScope","withScope","showReportDialog"].forEach((function(e){n[i][e]=function(){h({f:e,a:arguments})}})),n.addEventListener(r,y),n.addEventListener(t,E),s||setTimeout((function(){O()}))}
 (
   window,
   document,
diff --git a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/init.js b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/init.js
index aa799f411980..8b137891791f 100644
--- a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/init.js
@@ -1,3 +1 @@
-import * as Sentry from '@sentry/browser';
 
-window.Sentry = Sentry;
diff --git a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/pageloadTransaction/init.js b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/pageloadTransaction/init.js
index a44e16bcf7d9..a8dad11a125f 100644
--- a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/pageloadTransaction/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/pageloadTransaction/init.js
@@ -1,4 +1 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
 window._testBaseTimestamp = performance.timeOrigin / 1000;
diff --git a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/replay/init.js b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/replay/init.js
index aa799f411980..8b137891791f 100644
--- a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/replay/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/replay/init.js
@@ -1,3 +1 @@
-import * as Sentry from '@sentry/browser';
 
-window.Sentry = Sentry;
diff --git a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/sdkLoadedInMeanwhile/subject.js b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/sdkLoadedInMeanwhile/subject.js
index 8b78a79beadb..46296b3b8c05 100644
--- a/packages/browser-integration-tests/loader-suites/loader/noOnLoad/sdkLoadedInMeanwhile/subject.js
+++ b/packages/browser-integration-tests/loader-suites/loader/noOnLoad/sdkLoadedInMeanwhile/subject.js
@@ -3,7 +3,7 @@ setTimeout(() => {
   cdnScript.src = '/cdn.bundle.js';
 
   cdnScript.addEventListener('load', () => {
-    window.Sentry.init({
+    Sentry.init({
       dsn: 'https://public@dsn.ingest.sentry.io/1337',
       replaysSessionSampleRate: 0.42,
     });
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/init.js
index 71a703f2f9e1..8c8c99e30367 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/init.js
@@ -1,7 +1,5 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 Sentry.onLoad(function () {
+  // You _have_ to call Sentry.init() before calling Sentry.captureException() in Sentry.onLoad()!
+  Sentry.init();
   Sentry.captureException('Test exception');
 });
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/test.ts b/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/test.ts
index b63a8d6db1e4..b3cf79bde5c2 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/test.ts
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/captureExceptionInOnLoad/test.ts
@@ -4,6 +4,14 @@ import { sentryTest } from '../../../../utils/fixtures';
 import { envelopeRequestParser, waitForErrorRequestOnUrl } from '../../../../utils/helpers';
 
 sentryTest('captureException works inside of onLoad', async ({ getLocalTestUrl, page }) => {
+  await page.route('https://dsn.ingest.sentry.io/**/*', route => {
+    return route.fulfill({
+      status: 200,
+      contentType: 'application/json',
+      body: JSON.stringify({ id: 'test-id' }),
+    });
+  });
+
   const url = await getLocalTestUrl({ testDir: __dirname });
   const req = await waitForErrorRequestOnUrl(page, url);
 
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customBrowserTracing/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/customBrowserTracing/init.js
index cf30bc698e53..269593b620f1 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/customBrowserTracing/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customBrowserTracing/init.js
@@ -1,6 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
 window._testBaseTimestamp = performance.timeOrigin / 1000;
 
 Sentry.onLoad(function () {
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/init.js
new file mode 100644
index 000000000000..4a9e000fd1c2
--- /dev/null
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/init.js
@@ -0,0 +1,20 @@
+window.__sentryOnLoad = 0;
+
+setTimeout(() => {
+  Sentry.onLoad(function () {
+    window.__hadSentry = window.sentryIsLoaded();
+
+    Sentry.init({
+      sampleRate: 0.5,
+    });
+
+    window.__sentryOnLoad++;
+  });
+});
+
+window.sentryIsLoaded = () => {
+  const __sentry = window.__SENTRY__;
+
+  // If there is a global __SENTRY__ that means that in any of the callbacks init() was already invoked
+  return !!(!(typeof __sentry === 'undefined') && __sentry.hub && __sentry.hub.getClient());
+};
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/test.ts b/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/test.ts
new file mode 100644
index 000000000000..eeea9de48fb2
--- /dev/null
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customInit/test.ts
@@ -0,0 +1,34 @@
+import { expect } from '@playwright/test';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { LOADER_CONFIGS } from '../../../../utils/generatePlugin';
+
+const bundle = process.env.PW_BUNDLE || '';
+const isLazy = LOADER_CONFIGS[bundle]?.lazy;
+
+sentryTest('always calls onLoad init correctly', async ({ getLocalTestUrl, page }) => {
+  await page.route('https://dsn.ingest.sentry.io/**/*', route => {
+    return route.fulfill({
+      status: 200,
+      contentType: 'application/json',
+      body: JSON.stringify({ id: 'test-id' }),
+    });
+  });
+
+  const url = await getLocalTestUrl({ testDir: __dirname });
+
+  await page.goto(url);
+
+  // We want to test that if we are _not_ lazy, we are correctly calling onLoad init()
+  // But if we are lazy and call `forceLoad`, we also call the onLoad init() correctly
+  if (isLazy) {
+    expect(await page.evaluate('window.__sentryOnLoad')).toEqual(0);
+    await page.evaluate('Sentry.forceLoad()');
+  }
+
+  await page.waitForFunction('window.__sentryOnLoad && window.sentryIsLoaded()');
+
+  expect(await page.evaluate('window.__hadSentry')).toEqual(false);
+  expect(await page.evaluate('window.__sentryOnLoad')).toEqual(1);
+  expect(await page.evaluate('Sentry.getCurrentHub().getClient().getOptions().sampleRate')).toEqual(0.5);
+});
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrations/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrations/init.js
index a5440c1979c5..5d2920680cfc 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrations/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrations/init.js
@@ -1,7 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 class CustomIntegration {
   constructor() {
     this.name = 'CustomIntegration';
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrationsFunction/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrationsFunction/init.js
index 4c1e600794d5..0836f8b3b887 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrationsFunction/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customIntegrationsFunction/init.js
@@ -1,7 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 class CustomIntegration {
   constructor() {
     this.name = 'CustomIntegration';
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/customReplay/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/customReplay/init.js
index 64d2463ed668..921209ce14dc 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/customReplay/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/customReplay/init.js
@@ -1,7 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 Sentry.onLoad(function () {
   Sentry.init({
     integrations: [
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/init.js
index 5a9398da8d47..e63705186b2f 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/init.js
@@ -1,7 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 Sentry.onLoad(function () {
   Sentry.init({});
 });
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/init.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/subject.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/subject.js
new file mode 100644
index 000000000000..1dcef58798cc
--- /dev/null
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/subject.js
@@ -0,0 +1,7 @@
+Sentry.forceLoad();
+
+setTimeout(() => {
+  Sentry.onLoad(function () {
+    Sentry.captureException('Test exception');
+  });
+}, 200);
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/test.ts b/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/test.ts
new file mode 100644
index 000000000000..46bbf81f3c58
--- /dev/null
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/onLoadLate/test.ts
@@ -0,0 +1,21 @@
+import { expect } from '@playwright/test';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { envelopeRequestParser, waitForErrorRequestOnUrl } from '../../../../utils/helpers';
+
+sentryTest('late onLoad call is handled', async ({ getLocalTestUrl, page }) => {
+  await page.route('https://dsn.ingest.sentry.io/**/*', route => {
+    return route.fulfill({
+      status: 200,
+      contentType: 'application/json',
+      body: JSON.stringify({ id: 'test-id' }),
+    });
+  });
+
+  const url = await getLocalTestUrl({ testDir: __dirname });
+  const req = await waitForErrorRequestOnUrl(page, url);
+
+  const eventData = envelopeRequestParser(req);
+
+  expect(eventData.message).toBe('Test exception');
+});
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/pageloadTransaction/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/pageloadTransaction/init.js
index dcb6c3e90d0d..7c0fceed58a4 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/pageloadTransaction/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/pageloadTransaction/init.js
@@ -1,6 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
 window._testBaseTimestamp = performance.timeOrigin / 1000;
 
 Sentry.onLoad(function () {
diff --git a/packages/browser-integration-tests/loader-suites/loader/onLoad/replay/init.js b/packages/browser-integration-tests/loader-suites/loader/onLoad/replay/init.js
index 5a9398da8d47..e63705186b2f 100644
--- a/packages/browser-integration-tests/loader-suites/loader/onLoad/replay/init.js
+++ b/packages/browser-integration-tests/loader-suites/loader/onLoad/replay/init.js
@@ -1,7 +1,3 @@
-import * as Sentry from '@sentry/browser';
-
-window.Sentry = Sentry;
-
 Sentry.onLoad(function () {
   Sentry.init({});
 });