diff --git a/.size-limit.js b/.size-limit.js
index 8b506b8f683b..4903d38fef62 100644
--- a/.size-limit.js
+++ b/.size-limit.js
@@ -79,7 +79,7 @@ module.exports = [
     path: 'packages/browser/build/npm/esm/index.js',
     import: createImport('init', 'browserTracingIntegration', 'replayIntegration', 'replayCanvasIntegration'),
     gzip: true,
-    limit: '78.1 KB',
+    limit: '78.2 KB',
   },
   {
     name: '@sentry/browser (incl. Tracing, Replay, Feedback)',
diff --git a/packages/browser-utils/src/metrics/browserMetrics.ts b/packages/browser-utils/src/metrics/browserMetrics.ts
index 278ce9c9784e..09714e90c11f 100644
--- a/packages/browser-utils/src/metrics/browserMetrics.ts
+++ b/packages/browser-utils/src/metrics/browserMetrics.ts
@@ -1,5 +1,5 @@
 /* eslint-disable max-lines */
-import { SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN, getActiveSpan, startInactiveSpan } from '@sentry/core';
+import { SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN, getActiveSpan } from '@sentry/core';
 import { setMeasurement } from '@sentry/core';
 import type { Measurements, Span, SpanAttributes, StartSpanOptions } from '@sentry/types';
 import { browserPerformanceTimeOrigin, getComponentName, htmlTreeAsString, logger, parseUrl } from '@sentry/utils';
diff --git a/packages/nextjs/src/client/index.ts b/packages/nextjs/src/client/index.ts
index c50bbce37305..a1e6aba11308 100644
--- a/packages/nextjs/src/client/index.ts
+++ b/packages/nextjs/src/client/index.ts
@@ -16,7 +16,7 @@ export * from '@sentry/react';
 export { captureUnderscoreErrorException } from '../common/pages-router-instrumentation/_error';
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __rewriteFramesAssetPrefixPath__: string;
+  _sentryRewriteFramesAssetPrefixPath: string;
 };
 
 // Treeshakable guard to remove all code related to tracing
@@ -64,7 +64,10 @@ function getDefaultIntegrations(options: BrowserOptions): Integration[] {
 
   // This value is injected at build time, based on the output directory specified in the build config. Though a default
   // is set there, we set it here as well, just in case something has gone wrong with the injection.
-  const assetPrefixPath = globalWithInjectedValues.__rewriteFramesAssetPrefixPath__ || '';
+  const assetPrefixPath =
+    process.env._sentryRewriteFramesAssetPrefixPath ||
+    globalWithInjectedValues._sentryRewriteFramesAssetPrefixPath ||
+    '';
   customDefaultIntegrations.push(nextjsClientStackFrameNormalizationIntegration({ assetPrefixPath }));
 
   return customDefaultIntegrations;
diff --git a/packages/nextjs/src/client/tunnelRoute.ts b/packages/nextjs/src/client/tunnelRoute.ts
index 3c93b93e41f2..59ce4cfe82b7 100644
--- a/packages/nextjs/src/client/tunnelRoute.ts
+++ b/packages/nextjs/src/client/tunnelRoute.ts
@@ -4,14 +4,14 @@ import { GLOBAL_OBJ, dsnFromString, logger } from '@sentry/utils';
 import { DEBUG_BUILD } from '../common/debug-build';
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __sentryRewritesTunnelPath__?: string;
+  _sentryRewritesTunnelPath?: string;
 };
 
 /**
  * Applies the `tunnel` option to the Next.js SDK options based on `withSentryConfig`'s `tunnelRoute` option.
  */
 export function applyTunnelRouteOption(options: BrowserOptions): void {
-  const tunnelRouteOption = globalWithInjectedValues.__sentryRewritesTunnelPath__;
+  const tunnelRouteOption = process.env._sentryRewritesTunnelPath || globalWithInjectedValues._sentryRewritesTunnelPath;
   if (tunnelRouteOption && options.dsn) {
     const dsnComponents = dsnFromString(options.dsn);
     if (!dsnComponents) {
diff --git a/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts b/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
index 6c37859a851d..143bf6fef6ef 100644
--- a/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
+++ b/packages/nextjs/src/common/devErrorSymbolicationEventProcessor.ts
@@ -11,7 +11,7 @@ type OriginalStackFrameResponse = {
 };
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __sentryBasePath?: string;
+  _sentryBasePath?: string;
 };
 
 async function resolveStackFrame(
@@ -32,7 +32,7 @@ async function resolveStackFrame(
       params.append(key, (frame[key as keyof typeof frame] ?? '').toString());
     });
 
-    let basePath = globalWithInjectedValues.__sentryBasePath ?? '';
+    let basePath = process.env._sentryBasePath ?? globalWithInjectedValues._sentryBasePath ?? '';
 
     // Prefix the basepath with a slash if it doesn't have one
     if (basePath !== '' && !basePath.match(/^\//)) {
diff --git a/packages/nextjs/src/config/types.ts b/packages/nextjs/src/config/types.ts
index d887369606b6..14be35215cf2 100644
--- a/packages/nextjs/src/config/types.ts
+++ b/packages/nextjs/src/config/types.ts
@@ -47,6 +47,8 @@ export type NextConfigObject = {
     clientTraceMetadata?: string[];
   };
   productionBrowserSourceMaps?: boolean;
+  // https://nextjs.org/docs/pages/api-reference/next-config-js/env
+  env?: Record<string, string>;
 };
 
 export type SentryBuildOptions = {
@@ -548,7 +550,7 @@ export type ModuleRuleUseProperty = {
  * Global with values we add when we inject code into people's pages, for use at runtime.
  */
 export type EnhancedGlobal = typeof GLOBAL_OBJ & {
-  __rewriteFramesDistDir__?: string;
+  _sentryRewriteFramesDistDir?: string;
   SENTRY_RELEASE?: { id: string };
   SENTRY_RELEASES?: { [key: string]: { id: string } };
 };
diff --git a/packages/nextjs/src/config/webpack.ts b/packages/nextjs/src/config/webpack.ts
index 6b96b96ecec1..b83008a4817e 100644
--- a/packages/nextjs/src/config/webpack.ts
+++ b/packages/nextjs/src/config/webpack.ts
@@ -562,6 +562,8 @@ function setUpModuleRules(newConfig: WebpackConfigObject): WebpackConfigObjectWi
 /**
  * Adds loaders to inject values on the global object based on user configuration.
  */
+// TODO(v9): Remove this loader and replace it with a nextConfig.env (https://web.archive.org/web/20240917153554/https://nextjs.org/docs/app/api-reference/next-config-js/env) or define based (https://github.com/vercel/next.js/discussions/71476) approach.
+// In order to remove this loader though we need to make sure the minimum supported Next.js version includes this PR (https://github.com/vercel/next.js/pull/61194), otherwise the nextConfig.env based approach will not work, as our SDK code is not processed by Next.js.
 function addValueInjectionLoader(
   newConfig: WebpackConfigObjectWithModuleRules,
   userNextConfig: NextConfigObject,
@@ -572,7 +574,7 @@ function addValueInjectionLoader(
 
   const isomorphicValues = {
     // `rewritesTunnel` set by the user in Next.js config
-    __sentryRewritesTunnelPath__:
+    _sentryRewritesTunnelPath:
       userSentryOptions.tunnelRoute !== undefined && userNextConfig.output !== 'export'
         ? `${userNextConfig.basePath ?? ''}${userSentryOptions.tunnelRoute}`
         : undefined,
@@ -582,21 +584,21 @@ function addValueInjectionLoader(
     SENTRY_RELEASE: buildContext.dev
       ? undefined
       : { id: userSentryOptions.release?.name ?? getSentryRelease(buildContext.buildId) },
-    __sentryBasePath: buildContext.dev ? userNextConfig.basePath : undefined,
+    _sentryBasePath: buildContext.dev ? userNextConfig.basePath : undefined,
   };
 
   const serverValues = {
     ...isomorphicValues,
     // Make sure that if we have a windows path, the backslashes are interpreted as such (rather than as escape
     // characters)
-    __rewriteFramesDistDir__: userNextConfig.distDir?.replace(/\\/g, '\\\\') || '.next',
+    _sentryRewriteFramesDistDir: userNextConfig.distDir?.replace(/\\/g, '\\\\') || '.next',
   };
 
   const clientValues = {
     ...isomorphicValues,
     // Get the path part of `assetPrefix`, minus any trailing slash. (We use a placeholder for the origin if
     // `assetPrefix` doesn't include one. Since we only care about the path, it doesn't matter what it is.)
-    __rewriteFramesAssetPrefixPath__: assetPrefix
+    _sentryRewriteFramesAssetPrefixPath: assetPrefix
       ? new URL(assetPrefix, 'http://dogs.are.great').pathname.replace(/\/$/, '')
       : '',
   };
diff --git a/packages/nextjs/src/config/withSentryConfig.ts b/packages/nextjs/src/config/withSentryConfig.ts
index 4f5205fecfcb..539e75c20596 100644
--- a/packages/nextjs/src/config/withSentryConfig.ts
+++ b/packages/nextjs/src/config/withSentryConfig.ts
@@ -20,6 +20,7 @@ let showedExportModeTunnelWarning = false;
  * @param sentryBuildOptions Additional options to configure instrumentation and
  * @returns The modified config to be exported
  */
+// TODO(v9): Always return an async function here to allow us to do async things like grabbing a deterministic build ID.
 export function withSentryConfig<C>(nextConfig?: C, sentryBuildOptions: SentryBuildOptions = {}): C {
   const castNextConfig = (nextConfig as NextConfig) || {};
   if (typeof castNextConfig === 'function') {
@@ -73,6 +74,8 @@ function getFinalConfigObject(
     }
   }
 
+  setUpBuildTimeVariables(incomingUserNextConfigObject, userSentryOptions);
+
   const nextJsVersion = getNextjsVersion();
 
   // Add the `clientTraceMetadata` experimental option based on Next.js version. The option got introduced in Next.js version 15.0.0 (actually 14.3.0-canary.64).
@@ -253,6 +256,43 @@ function setUpTunnelRewriteRules(userNextConfig: NextConfigObject, tunnelPath: s
   };
 }
 
+// TODO(v9): Inject the release into all the bundles. This is breaking because grabbing the build ID if the user provides
+// it in `generateBuildId` (https://nextjs.org/docs/app/api-reference/next-config-js/generateBuildId) is async but we do
+// not turn the next config function in the type it was passed.
+function setUpBuildTimeVariables(userNextConfig: NextConfigObject, userSentryOptions: SentryBuildOptions): void {
+  const assetPrefix = userNextConfig.assetPrefix || userNextConfig.basePath || '';
+  const basePath = userNextConfig.basePath ?? '';
+  const rewritesTunnelPath =
+    userSentryOptions.tunnelRoute !== undefined && userNextConfig.output !== 'export'
+      ? `${basePath}${userSentryOptions.tunnelRoute}`
+      : undefined;
+
+  const buildTimeVariables: Record<string, string> = {
+    // Make sure that if we have a windows path, the backslashes are interpreted as such (rather than as escape
+    // characters)
+    _sentryRewriteFramesDistDir: userNextConfig.distDir?.replace(/\\/g, '\\\\') || '.next',
+    // Get the path part of `assetPrefix`, minus any trailing slash. (We use a placeholder for the origin if
+    // `assetPrefix` doesn't include one. Since we only care about the path, it doesn't matter what it is.)
+    _sentryRewriteFramesAssetPrefixPath: assetPrefix
+      ? new URL(assetPrefix, 'http://dogs.are.great').pathname.replace(/\/$/, '')
+      : '',
+  };
+
+  if (rewritesTunnelPath) {
+    buildTimeVariables._sentryRewritesTunnelPath = rewritesTunnelPath;
+  }
+
+  if (basePath) {
+    buildTimeVariables._sentryBasePath = basePath;
+  }
+
+  if (typeof userNextConfig.env === 'object') {
+    userNextConfig.env = { ...buildTimeVariables, ...userNextConfig.env };
+  } else if (userNextConfig.env === undefined) {
+    userNextConfig.env = buildTimeVariables;
+  }
+}
+
 function getNextjsVersion(): string | undefined {
   const nextjsPackageJsonPath = resolveNextjsPackageJson();
   if (nextjsPackageJsonPath) {
diff --git a/packages/nextjs/src/edge/index.ts b/packages/nextjs/src/edge/index.ts
index fff4236bf3be..5bfc8cca054b 100644
--- a/packages/nextjs/src/edge/index.ts
+++ b/packages/nextjs/src/edge/index.ts
@@ -21,7 +21,7 @@ export { captureUnderscoreErrorException } from '../common/pages-router-instrume
 export type EdgeOptions = VercelEdgeOptions;
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __rewriteFramesDistDir__?: string;
+  _sentryRewriteFramesDistDir?: string;
 };
 
 /** Inits the Sentry NextJS SDK on the Edge Runtime. */
@@ -36,7 +36,7 @@ export function init(options: VercelEdgeOptions = {}): void {
 
   // This value is injected at build time, based on the output directory specified in the build config. Though a default
   // is set there, we set it here as well, just in case something has gone wrong with the injection.
-  const distDirName = globalWithInjectedValues.__rewriteFramesDistDir__;
+  const distDirName = process.env._sentryRewriteFramesDistDir || globalWithInjectedValues._sentryRewriteFramesDistDir;
 
   if (distDirName) {
     customDefaultIntegrations.push(distDirRewriteFramesIntegration({ distDirName }));
diff --git a/packages/nextjs/src/edge/rewriteFramesIntegration.ts b/packages/nextjs/src/edge/rewriteFramesIntegration.ts
index 84d5a41b0922..15a541311ed1 100644
--- a/packages/nextjs/src/edge/rewriteFramesIntegration.ts
+++ b/packages/nextjs/src/edge/rewriteFramesIntegration.ts
@@ -3,7 +3,7 @@ import type { IntegrationFn, StackFrame } from '@sentry/types';
 import { GLOBAL_OBJ, escapeStringForRegex } from '@sentry/utils';
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __rewriteFramesDistDir__?: string;
+  _sentryRewriteFramesDistDir?: string;
 };
 
 type StackFrameIteratee = (frame: StackFrame) => StackFrame;
@@ -14,9 +14,8 @@ interface RewriteFramesOptions {
 }
 
 export const customRewriteFramesIntegration = ((options?: RewriteFramesOptions) => {
-  // This value is injected at build time, based on the output directory specified in the build config. Though a default
-  // is set there, we set it here as well, just in case something has gone wrong with the injection.
-  const distDirName = globalWithInjectedValues.__rewriteFramesDistDir__;
+  // This value is injected at build time, based on the output directory specified in the build config.
+  const distDirName = process.env._sentryRewriteFramesDistDir || globalWithInjectedValues._sentryRewriteFramesDistDir;
 
   if (distDirName) {
     const distDirAbsPath = distDirName.replace(/(\/|\\)$/, ''); // We strip trailing slashes because "app:///_next" also doesn't have one
diff --git a/packages/nextjs/src/server/index.ts b/packages/nextjs/src/server/index.ts
index 7aade8cbd5c3..bdff0de922b2 100644
--- a/packages/nextjs/src/server/index.ts
+++ b/packages/nextjs/src/server/index.ts
@@ -42,8 +42,8 @@ export * from '@sentry/node';
 export { captureUnderscoreErrorException } from '../common/pages-router-instrumentation/_error';
 
 const globalWithInjectedValues = GLOBAL_OBJ as typeof GLOBAL_OBJ & {
-  __rewriteFramesDistDir__?: string;
-  __sentryRewritesTunnelPath__?: string;
+  _sentryRewriteFramesDistDir?: string;
+  _sentryRewritesTunnelPath?: string;
 };
 
 /**
@@ -109,7 +109,7 @@ export function init(options: NodeOptions): NodeClient | undefined {
 
   // This value is injected at build time, based on the output directory specified in the build config. Though a default
   // is set there, we set it here as well, just in case something has gone wrong with the injection.
-  const distDirName = globalWithInjectedValues.__rewriteFramesDistDir__;
+  const distDirName = process.env._sentryRewriteFramesDistDir || globalWithInjectedValues._sentryRewriteFramesDistDir;
   if (distDirName) {
     customDefaultIntegrations.push(distDirRewriteFramesIntegration({ distDirName }));
   }
@@ -212,8 +212,10 @@ export function init(options: NodeOptions): NodeClient | undefined {
 
           // Filter out transactions for requests to the tunnel route
           if (
-            globalWithInjectedValues.__sentryRewritesTunnelPath__ &&
-            event.transaction === `POST ${globalWithInjectedValues.__sentryRewritesTunnelPath__}`
+            (globalWithInjectedValues._sentryRewritesTunnelPath &&
+              event.transaction === `POST ${globalWithInjectedValues._sentryRewritesTunnelPath}`) ||
+            (process.env._sentryRewritesTunnelPath &&
+              event.transaction === `POST ${process.env._sentryRewritesTunnelPath}`)
           ) {
             return null;
           }
diff --git a/packages/nextjs/src/server/rewriteFramesIntegration.ts b/packages/nextjs/src/server/rewriteFramesIntegration.ts
index 6438ccb0d922..33bc7d90cb99 100644
--- a/packages/nextjs/src/server/rewriteFramesIntegration.ts
+++ b/packages/nextjs/src/server/rewriteFramesIntegration.ts
@@ -4,7 +4,7 @@ import type { IntegrationFn, StackFrame } from '@sentry/types';
 import { escapeStringForRegex } from '@sentry/utils';
 
 const globalWithInjectedValues = global as typeof global & {
-  __rewriteFramesDistDir__?: string;
+  _sentryRewriteFramesDistDir?: string;
 };
 
 type StackFrameIteratee = (frame: StackFrame) => StackFrame;
@@ -17,7 +17,7 @@ interface RewriteFramesOptions {
 export const customRewriteFramesIntegration = ((options?: RewriteFramesOptions) => {
   // This value is injected at build time, based on the output directory specified in the build config. Though a default
   // is set there, we set it here as well, just in case something has gone wrong with the injection.
-  const distDirName = globalWithInjectedValues.__rewriteFramesDistDir__;
+  const distDirName = process.env._sentryRewriteFramesDistDir || globalWithInjectedValues._sentryRewriteFramesDistDir;
 
   if (distDirName) {
     // nextjs always puts the build directory at the project root level, which is also where you run `next start` from, so
diff --git a/packages/nextjs/test/serverSdk.test.ts b/packages/nextjs/test/serverSdk.test.ts
index 1129bcdbbf2b..fed88fe25d33 100644
--- a/packages/nextjs/test/serverSdk.test.ts
+++ b/packages/nextjs/test/serverSdk.test.ts
@@ -6,7 +6,7 @@ import { GLOBAL_OBJ } from '@sentry/utils';
 import { init } from '../src/server';
 
 // normally this is set as part of the build process, so mock it here
-(GLOBAL_OBJ as typeof GLOBAL_OBJ & { __rewriteFramesDistDir__: string }).__rewriteFramesDistDir__ = '.next';
+(GLOBAL_OBJ as typeof GLOBAL_OBJ & { _sentryRewriteFramesDistDir: string })._sentryRewriteFramesDistDir = '.next';
 
 const nodeInit = jest.spyOn(SentryNode, 'init');
 
diff --git a/packages/nextjs/test/utils/tunnelRoute.test.ts b/packages/nextjs/test/utils/tunnelRoute.test.ts
index 576898c061b2..05aa992f39e6 100644
--- a/packages/nextjs/test/utils/tunnelRoute.test.ts
+++ b/packages/nextjs/test/utils/tunnelRoute.test.ts
@@ -3,16 +3,16 @@ import type { BrowserOptions } from '@sentry/react';
 import { applyTunnelRouteOption } from '../../src/client/tunnelRoute';
 
 const globalWithInjectedValues = global as typeof global & {
-  __sentryRewritesTunnelPath__?: string;
+  _sentryRewritesTunnelPath?: string;
 };
 
 beforeEach(() => {
-  globalWithInjectedValues.__sentryRewritesTunnelPath__ = undefined;
+  globalWithInjectedValues._sentryRewritesTunnelPath = undefined;
 });
 
 describe('applyTunnelRouteOption()', () => {
   it('Correctly applies `tunnelRoute` option when conditions are met', () => {
-    globalWithInjectedValues.__sentryRewritesTunnelPath__ = '/my-error-monitoring-route';
+    globalWithInjectedValues._sentryRewritesTunnelPath = '/my-error-monitoring-route';
     const options: any = {
       dsn: 'https://11111111111111111111111111111111@o2222222.ingest.sentry.io/3333333',
     } as BrowserOptions;
@@ -23,7 +23,7 @@ describe('applyTunnelRouteOption()', () => {
   });
 
   it("Doesn't apply `tunnelRoute` when DSN is missing", () => {
-    globalWithInjectedValues.__sentryRewritesTunnelPath__ = '/my-error-monitoring-route';
+    globalWithInjectedValues._sentryRewritesTunnelPath = '/my-error-monitoring-route';
     const options: any = {
       // no dsn
     } as BrowserOptions;
@@ -34,7 +34,7 @@ describe('applyTunnelRouteOption()', () => {
   });
 
   it("Doesn't apply `tunnelRoute` when DSN is invalid", () => {
-    globalWithInjectedValues.__sentryRewritesTunnelPath__ = '/my-error-monitoring-route';
+    globalWithInjectedValues._sentryRewritesTunnelPath = '/my-error-monitoring-route';
     const options: any = {
       dsn: 'invalidDsn',
     } as BrowserOptions;
@@ -55,7 +55,7 @@ describe('applyTunnelRouteOption()', () => {
   });
 
   it("Doesn't `tunnelRoute` option when DSN is not a SaaS DSN", () => {
-    globalWithInjectedValues.__sentryRewritesTunnelPath__ = '/my-error-monitoring-route';
+    globalWithInjectedValues._sentryRewritesTunnelPath = '/my-error-monitoring-route';
     const options: any = {
       dsn: 'https://11111111111111111111111111111111@example.com/3333333',
     } as BrowserOptions;
@@ -66,7 +66,7 @@ describe('applyTunnelRouteOption()', () => {
   });
 
   it('Correctly applies `tunnelRoute` option to region DSNs', () => {
-    globalWithInjectedValues.__sentryRewritesTunnelPath__ = '/my-error-monitoring-route';
+    globalWithInjectedValues._sentryRewritesTunnelPath = '/my-error-monitoring-route';
     const options: any = {
       dsn: 'https://11111111111111111111111111111111@o2222222.ingest.us.sentry.io/3333333',
     } as BrowserOptions;