diff --git a/.size-limit.js b/.size-limit.js
index 5ccf34d416c0..10aa99dd8954 100644
--- a/.size-limit.js
+++ b/.size-limit.js
@@ -150,7 +150,7 @@ module.exports = [
     name: 'CDN Bundle',
     path: createCDNPath('bundle.min.js'),
     gzip: true,
-    limit: '27 KB',
+    limit: '27.5 KB',
   },
   {
     name: 'CDN Bundle (incl. Tracing)',
@@ -183,7 +183,7 @@ module.exports = [
     path: createCDNPath('bundle.tracing.min.js'),
     gzip: false,
     brotli: false,
-    limit: '123 KB',
+    limit: '124 KB',
   },
   {
     name: 'CDN Bundle (incl. Tracing, Replay) - uncompressed',
diff --git a/dev-packages/e2e-tests/test-applications/cloudflare-workers/tests/index.test.ts b/dev-packages/e2e-tests/test-applications/cloudflare-workers/tests/index.test.ts
index ad63c1a0d307..8c09693c81ed 100644
--- a/dev-packages/e2e-tests/test-applications/cloudflare-workers/tests/index.test.ts
+++ b/dev-packages/e2e-tests/test-applications/cloudflare-workers/tests/index.test.ts
@@ -1,5 +1,6 @@
 import { expect, test } from '@playwright/test';
-import { waitForError } from '@sentry-internal/test-utils';
+import { waitForError, waitForRequest } from '@sentry-internal/test-utils';
+import { SDK_VERSION } from '@sentry/cloudflare';
 import { WebSocket } from 'ws';
 
 test('Index page', async ({ baseURL }) => {
@@ -69,3 +70,15 @@ test('Websocket.webSocketClose', async ({ baseURL }) => {
   expect(event.exception?.values?.[0]?.value).toBe('Should be recorded in Sentry: webSocketClose');
   expect(event.exception?.values?.[0]?.mechanism?.type).toBe('auto.faas.cloudflare.durable_object');
 });
+
+test('sends user-agent header with SDK name and version in envelope requests', async ({ baseURL }) => {
+  const requestPromise = waitForRequest('cloudflare-workers', () => true);
+
+  await fetch(`${baseURL}/throwException`);
+
+  const request = await requestPromise;
+
+  expect(request.rawProxyRequestHeaders).toMatchObject({
+    'user-agent': `sentry.javascript.cloudflare/${SDK_VERSION}`,
+  });
+});
diff --git a/dev-packages/e2e-tests/test-applications/node-express/tests/misc.test.ts b/dev-packages/e2e-tests/test-applications/node-express/tests/misc.test.ts
new file mode 100644
index 000000000000..427c70b6fa21
--- /dev/null
+++ b/dev-packages/e2e-tests/test-applications/node-express/tests/misc.test.ts
@@ -0,0 +1,15 @@
+import { expect, test } from '@playwright/test';
+import { waitForRequest } from '@sentry-internal/test-utils';
+import { SDK_VERSION } from '@sentry/node';
+
+test('sends user-agent header with SDK name and version in envelope requests', async ({ baseURL }) => {
+  const requestPromise = waitForRequest('node-express', () => true);
+
+  await fetch(`${baseURL}/test-exception/123`);
+
+  const request = await requestPromise;
+
+  expect(request.rawProxyRequestHeaders).toMatchObject({
+    'user-agent': `sentry.javascript.node/${SDK_VERSION}`,
+  });
+});
diff --git a/dev-packages/test-utils/src/event-proxy-server.ts b/dev-packages/test-utils/src/event-proxy-server.ts
index 0becf5a743f2..08fa39db950f 100644
--- a/dev-packages/test-utils/src/event-proxy-server.ts
+++ b/dev-packages/test-utils/src/event-proxy-server.ts
@@ -24,6 +24,7 @@ interface EventProxyServerOptions {
 interface SentryRequestCallbackData {
   envelope: Envelope;
   rawProxyRequestBody: string;
+  rawProxyRequestHeaders: Record<string, string | string[] | undefined>;
   rawSentryResponseBody: string;
   sentryResponseStatusCode?: number;
 }
@@ -182,6 +183,7 @@ export async function startEventProxyServer(options: EventProxyServerOptions): P
     const data: SentryRequestCallbackData = {
       envelope: parseEnvelope(proxyRequestBody),
       rawProxyRequestBody: proxyRequestBody,
+      rawProxyRequestHeaders: proxyRequest.headers,
       rawSentryResponseBody: '',
       sentryResponseStatusCode: 200,
     };
diff --git a/packages/browser/src/transports/types.ts b/packages/browser/src/transports/types.ts
index fd8c4a93fdd6..a304e9f93d66 100644
--- a/packages/browser/src/transports/types.ts
+++ b/packages/browser/src/transports/types.ts
@@ -3,6 +3,4 @@ import type { BaseTransportOptions } from '@sentry/core';
 export interface BrowserTransportOptions extends BaseTransportOptions {
   /** Fetch API init parameters. Used by the FetchTransport */
   fetchOptions?: RequestInit;
-  /** Custom headers for the transport. Used by the XHRTransport and FetchTransport */
-  headers?: { [key: string]: string };
 }
diff --git a/packages/bun/src/transports/index.ts b/packages/bun/src/transports/index.ts
index 7a27846548b3..20df5bb4b521 100644
--- a/packages/bun/src/transports/index.ts
+++ b/packages/bun/src/transports/index.ts
@@ -1,15 +1,10 @@
 import type { BaseTransportOptions, Transport, TransportMakeRequestResponse, TransportRequest } from '@sentry/core';
 import { createTransport, suppressTracing } from '@sentry/core';
 
-export interface BunTransportOptions extends BaseTransportOptions {
-  /** Custom headers for the transport. Used by the XHRTransport and FetchTransport */
-  headers?: { [key: string]: string };
-}
-
 /**
  * Creates a Transport that uses the Fetch API to send events to Sentry.
  */
-export function makeFetchTransport(options: BunTransportOptions): Transport {
+export function makeFetchTransport(options: BaseTransportOptions): Transport {
   function makeRequest(request: TransportRequest): PromiseLike<TransportMakeRequestResponse> {
     const requestOptions: RequestInit = {
       body: request.body,
diff --git a/packages/bun/src/types.ts b/packages/bun/src/types.ts
index 755eb3e48a0a..afec75d1ee8d 100644
--- a/packages/bun/src/types.ts
+++ b/packages/bun/src/types.ts
@@ -1,5 +1,4 @@
-import type { ClientOptions, Options, TracePropagationTargets } from '@sentry/core';
-import type { BunTransportOptions } from './transports';
+import type { BaseTransportOptions, ClientOptions, Options, TracePropagationTargets } from '@sentry/core';
 
 export interface BaseBunOptions {
   /**
@@ -43,10 +42,10 @@ export interface BaseBunOptions {
  * Configuration options for the Sentry Bun SDK
  * @see @sentry/core Options for more information.
  */
-export interface BunOptions extends Options<BunTransportOptions>, BaseBunOptions {}
+export interface BunOptions extends Options<BaseTransportOptions>, BaseBunOptions {}
 
 /**
  * Configuration options for the Sentry Bun SDK Client class
  * @see BunClient for more information.
  */
-export interface BunClientOptions extends ClientOptions<BunTransportOptions>, BaseBunOptions {}
+export interface BunClientOptions extends ClientOptions<BaseTransportOptions>, BaseBunOptions {}
diff --git a/packages/cloudflare/src/transport.ts b/packages/cloudflare/src/transport.ts
index 2ac401505fbb..eee54bd7a790 100644
--- a/packages/cloudflare/src/transport.ts
+++ b/packages/cloudflare/src/transport.ts
@@ -4,8 +4,6 @@ import { createTransport, SENTRY_BUFFER_FULL_ERROR, suppressTracing } from '@sen
 export interface CloudflareTransportOptions extends BaseTransportOptions {
   /** Fetch API init parameters. */
   fetchOptions?: RequestInit;
-  /** Custom headers for the transport. */
-  headers?: { [key: string]: string };
 }
 
 const DEFAULT_TRANSPORT_BUFFER_SIZE = 30;
diff --git a/packages/core/src/server-runtime-client.ts b/packages/core/src/server-runtime-client.ts
index 9d037eb3b7c3..988e642d0a27 100644
--- a/packages/core/src/server-runtime-client.ts
+++ b/packages/core/src/server-runtime-client.ts
@@ -4,6 +4,7 @@ import { getIsolationScope } from './currentScopes';
 import { DEBUG_BUILD } from './debug-build';
 import type { Scope } from './scope';
 import { registerSpanErrorInstrumentation } from './tracing';
+import { addUserAgentToTransportHeaders } from './transports/userAgent';
 import type { CheckIn, MonitorConfig, SerializedCheckIn } from './types-hoist/checkin';
 import type { Event, EventHint } from './types-hoist/event';
 import type { ClientOptions } from './types-hoist/options';
@@ -36,6 +37,8 @@ export class ServerRuntimeClient<
     // Server clients always support tracing
     registerSpanErrorInstrumentation();
 
+    addUserAgentToTransportHeaders(options);
+
     super(options);
   }
 
diff --git a/packages/core/src/transports/userAgent.ts b/packages/core/src/transports/userAgent.ts
new file mode 100644
index 000000000000..5508640a855c
--- /dev/null
+++ b/packages/core/src/transports/userAgent.ts
@@ -0,0 +1,22 @@
+import type { ClientOptions } from '../types-hoist/options';
+
+/**
+ * Takes the SDK metadata and adds the user-agent header to the transport options.
+ * This ensures that the SDK sends the user-agent header with SDK name and version to
+ * all requests made by the transport.
+ *
+ * @see https://develop.sentry.dev/sdk/overview/#user-agent
+ */
+export function addUserAgentToTransportHeaders(options: ClientOptions): void {
+  const sdkMetadata = options._metadata?.sdk;
+  const sdkUserAgent =
+    sdkMetadata?.name && sdkMetadata?.version ? `${sdkMetadata?.name}/${sdkMetadata?.version}` : undefined;
+
+  options.transportOptions = {
+    ...options.transportOptions,
+    headers: {
+      ...(sdkUserAgent && { 'user-agent': sdkUserAgent }),
+      ...options.transportOptions?.headers,
+    },
+  };
+}
diff --git a/packages/core/src/types-hoist/transport.ts b/packages/core/src/types-hoist/transport.ts
index 8e0035c93137..320ed98b00e4 100644
--- a/packages/core/src/types-hoist/transport.ts
+++ b/packages/core/src/types-hoist/transport.ts
@@ -30,6 +30,11 @@ export interface BaseTransportOptions extends InternalBaseTransportOptions {
   // transport does not care about dsn specific - client should take care of
   // parsing and figuring that out
   url: string;
+
+  /**
+   * Custom HTTP headers to be added to requests made by the transport.
+   */
+  headers?: { [key: string]: string };
 }
 
 export interface Transport {
diff --git a/packages/core/test/lib/server-runtime-client.test.ts b/packages/core/test/lib/server-runtime-client.test.ts
index 525ee514c1a2..3c5fe874af9f 100644
--- a/packages/core/test/lib/server-runtime-client.test.ts
+++ b/packages/core/test/lib/server-runtime-client.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it, test, vi } from 'vitest';
-import { createTransport, Scope } from '../../src';
+import { applySdkMetadata, createTransport, Scope } from '../../src';
 import type { ServerRuntimeClientOptions } from '../../src/server-runtime-client';
 import { ServerRuntimeClient } from '../../src/server-runtime-client';
 import type { Event, EventHint } from '../../src/types-hoist/event';
@@ -205,4 +205,35 @@ describe('ServerRuntimeClient', () => {
       ]);
     });
   });
+
+  describe('user-agent header', () => {
+    it('sends user-agent header with SDK name and version', () => {
+      const options = getDefaultClientOptions({ dsn: PUBLIC_DSN });
+
+      // this is done in all `init` functions of the respective SDKs:
+      applySdkMetadata(options, 'core');
+
+      client = new ServerRuntimeClient(options);
+
+      expect(client.getOptions().transportOptions?.headers).toEqual({
+        'user-agent': 'sentry.javascript.core/0.0.0-unknown.0',
+      });
+    });
+
+    it('prefers user-passed headers (including user-agent)', () => {
+      const options = getDefaultClientOptions({
+        dsn: PUBLIC_DSN,
+        transportOptions: { headers: { 'x-custom-header': 'custom-value', 'user-agent': 'custom-user-agent' } },
+      });
+
+      applySdkMetadata(options, 'core');
+
+      client = new ServerRuntimeClient(options);
+
+      expect(client.getOptions().transportOptions?.headers).toEqual({
+        'user-agent': 'custom-user-agent',
+        'x-custom-header': 'custom-value',
+      });
+    });
+  });
 });
diff --git a/packages/deno/src/transports/index.ts b/packages/deno/src/transports/index.ts
index c5b6594b1c4d..521011fea6b8 100644
--- a/packages/deno/src/transports/index.ts
+++ b/packages/deno/src/transports/index.ts
@@ -1,15 +1,10 @@
 import type { BaseTransportOptions, Transport, TransportMakeRequestResponse, TransportRequest } from '@sentry/core';
 import { consoleSandbox, createTransport, debug, suppressTracing } from '@sentry/core';
 
-export interface DenoTransportOptions extends BaseTransportOptions {
-  /** Custom headers for the transport. Used by the XHRTransport and FetchTransport */
-  headers?: { [key: string]: string };
-}
-
 /**
  * Creates a Transport that uses the Fetch API to send events to Sentry.
  */
-export function makeFetchTransport(options: DenoTransportOptions): Transport {
+export function makeFetchTransport(options: BaseTransportOptions): Transport {
   const url = new URL(options.url);
 
   Deno.permissions
diff --git a/packages/deno/src/types.ts b/packages/deno/src/types.ts
index 1659e7a635e1..69eee4ae6313 100644
--- a/packages/deno/src/types.ts
+++ b/packages/deno/src/types.ts
@@ -1,5 +1,4 @@
-import type { ClientOptions, Options, TracePropagationTargets } from '@sentry/core';
-import type { DenoTransportOptions } from './transports';
+import type { BaseTransportOptions, ClientOptions, Options, TracePropagationTargets } from '@sentry/core';
 
 export interface BaseDenoOptions {
   /**
@@ -44,10 +43,10 @@ export interface BaseDenoOptions {
  * Configuration options for the Sentry Deno SDK
  * @see @sentry/core Options for more information.
  */
-export interface DenoOptions extends Options<DenoTransportOptions>, BaseDenoOptions {}
+export interface DenoOptions extends Options<BaseTransportOptions>, BaseDenoOptions {}
 
 /**
  * Configuration options for the Sentry Deno SDK Client class
  * @see DenoClient for more information.
  */
-export interface DenoClientOptions extends ClientOptions<DenoTransportOptions>, BaseDenoOptions {}
+export interface DenoClientOptions extends ClientOptions<BaseTransportOptions>, BaseDenoOptions {}
diff --git a/packages/node-core/src/transports/http.ts b/packages/node-core/src/transports/http.ts
index 49897dfa22b1..3319353aff14 100644
--- a/packages/node-core/src/transports/http.ts
+++ b/packages/node-core/src/transports/http.ts
@@ -14,8 +14,6 @@ import { HttpsProxyAgent } from '../proxy';
 import type { HTTPModule } from './http-module';
 
 export interface NodeTransportOptions extends BaseTransportOptions {
-  /** Define custom headers */
-  headers?: Record<string, string>;
   /** Set a proxy that should be used for outbound requests. */
   proxy?: string;
   /** HTTPS proxy CA certificates */
diff --git a/packages/node-core/test/sdk/client.test.ts b/packages/node-core/test/sdk/client.test.ts
index 01623f49f0a3..0bcef2669095 100644
--- a/packages/node-core/test/sdk/client.test.ts
+++ b/packages/node-core/test/sdk/client.test.ts
@@ -32,6 +32,11 @@ describe('NodeClient', () => {
       dsn: expect.any(String),
       integrations: [],
       transport: options.transport,
+      transportOptions: {
+        headers: {
+          'user-agent': `sentry.javascript.node/${SDK_VERSION}`,
+        },
+      },
       stackParser: options.stackParser,
       _metadata: {
         sdk: {
diff --git a/packages/node/test/sdk/client.test.ts b/packages/node/test/sdk/client.test.ts
index 7f57d4772212..ff58698a7931 100644
--- a/packages/node/test/sdk/client.test.ts
+++ b/packages/node/test/sdk/client.test.ts
@@ -31,6 +31,11 @@ describe('NodeClient', () => {
       dsn: expect.any(String),
       integrations: [],
       transport: options.transport,
+      transportOptions: {
+        headers: {
+          'user-agent': `sentry.javascript.node/${SDK_VERSION}`,
+        },
+      },
       stackParser: options.stackParser,
       _metadata: {
         sdk: {
diff --git a/packages/vercel-edge/src/transports/index.ts b/packages/vercel-edge/src/transports/index.ts
index bb8ea807764c..668fb6a4c236 100644
--- a/packages/vercel-edge/src/transports/index.ts
+++ b/packages/vercel-edge/src/transports/index.ts
@@ -4,8 +4,6 @@ import { createTransport, SENTRY_BUFFER_FULL_ERROR, suppressTracing } from '@sen
 export interface VercelEdgeTransportOptions extends BaseTransportOptions {
   /** Fetch API init parameters. */
   fetchOptions?: RequestInit;
-  /** Custom headers for the transport. */
-  headers?: { [key: string]: string };
 }
 
 const DEFAULT_TRANSPORT_BUFFER_SIZE = 30;