diff --git a/.changeset/preserve-request-meta-envelope-keys.md b/.changeset/preserve-request-meta-envelope-keys.md
new file mode 100644
index 0000000000..d45a2c825a
--- /dev/null
+++ b/.changeset/preserve-request-meta-envelope-keys.md
@@ -0,0 +1,6 @@
+---
+'@modelcontextprotocol/core-internal': patch
+'@modelcontextprotocol/server': patch
+---
+
+Publish `RequestMetaEnvelope` with its wire keys intact, so `ctx.mcpReq.envelope?.[CLIENT_CAPABILITIES_META_KEY]` is typed as `ClientCapabilities | undefined`. The 2.4.0 declaration emit dropped the computed keys and published the type as `{}`.
diff --git a/packages/core-internal/src/types/types.ts b/packages/core-internal/src/types/types.ts
index 61cc7f9b36..601e4b2ecf 100644
--- a/packages/core-internal/src/types/types.ts
+++ b/packages/core-internal/src/types/types.ts
@@ -4,17 +4,7 @@
 
 import type * as z from 'zod/v4';
 
-import type {
-    CLIENT_CAPABILITIES_META_KEY,
-    CLIENT_INFO_META_KEY,
-    INTERNAL_ERROR,
-    INVALID_PARAMS,
-    INVALID_REQUEST,
-    LOG_LEVEL_META_KEY,
-    METHOD_NOT_FOUND,
-    PARSE_ERROR,
-    PROTOCOL_VERSION_META_KEY
-} from './constants';
+import type { INTERNAL_ERROR, INVALID_PARAMS, INVALID_REQUEST, METHOD_NOT_FOUND, PARSE_ERROR } from './constants';
 import type {
     AnnotationsSchema,
     AudioContentSchema,
@@ -240,20 +230,22 @@ export type NotificationParams = Infer<typeof NotificationsParamsSchema>;
  * The per-request `_meta` envelope carried by every request under protocol revision
  * 2026-07-28 (protocol version, client info, client capabilities, optional log level).
  *
- * Neutral hand-written shape keyed by the public meta-key constants — never
- * inferred from a wire-module schema (this neutral layer does not import from
+ * Neutral hand-written shape whose keys are the public meta-key constant
+ * values, written as string literals so the tsdown declaration bundler
+ * cannot drop them (it published this type as `{}` in 2.4.0). Never inferred
+ * from a wire-module schema (this neutral layer does not import from
  * `wire/rev*`). A `type` alias rather than an interface so it stays assignable
  * to `_meta`'s string-indexed object slot.
  */
 export type RequestMetaEnvelope = {
-    [PROTOCOL_VERSION_META_KEY]: string;
+    'io.modelcontextprotocol/protocolVersion': string;
     /**
      * Optional since spec PR #3002: clients SHOULD send it, servers must not
      * require it (and should not rely on it for behavior or security).
      */
-    [CLIENT_INFO_META_KEY]?: Implementation;
-    [CLIENT_CAPABILITIES_META_KEY]: ClientCapabilities;
-    [LOG_LEVEL_META_KEY]?: LoggingLevel;
+    'io.modelcontextprotocol/clientInfo'?: Implementation;
+    'io.modelcontextprotocol/clientCapabilities': ClientCapabilities;
+    'io.modelcontextprotocol/logLevel'?: LoggingLevel;
 };
 
 /* Empty result */
diff --git a/packages/core-internal/test/types/requestMetaEnvelope.test.ts b/packages/core-internal/test/types/requestMetaEnvelope.test.ts
new file mode 100644
index 0000000000..922aa3c33b
--- /dev/null
+++ b/packages/core-internal/test/types/requestMetaEnvelope.test.ts
@@ -0,0 +1,21 @@
+import { describe, expectTypeOf, it } from 'vitest';
+
+import {
+    CLIENT_CAPABILITIES_META_KEY,
+    CLIENT_INFO_META_KEY,
+    LOG_LEVEL_META_KEY,
+    PROTOCOL_VERSION_META_KEY
+} from '../../src/types/constants';
+import type { ClientCapabilities, Implementation, LoggingLevel, RequestMetaEnvelope } from '../../src/types/types';
+
+describe('RequestMetaEnvelope', () => {
+    it('is keyed by the public meta-key constants', () => {
+        expectTypeOf<keyof RequestMetaEnvelope>().toEqualTypeOf<
+            typeof PROTOCOL_VERSION_META_KEY | typeof CLIENT_INFO_META_KEY | typeof CLIENT_CAPABILITIES_META_KEY | typeof LOG_LEVEL_META_KEY
+        >();
+        expectTypeOf<RequestMetaEnvelope[typeof PROTOCOL_VERSION_META_KEY]>().toEqualTypeOf<string>();
+        expectTypeOf<RequestMetaEnvelope[typeof CLIENT_INFO_META_KEY]>().toEqualTypeOf<Implementation | undefined>();
+        expectTypeOf<RequestMetaEnvelope[typeof CLIENT_CAPABILITIES_META_KEY]>().toEqualTypeOf<ClientCapabilities>();
+        expectTypeOf<RequestMetaEnvelope[typeof LOG_LEVEL_META_KEY]>().toEqualTypeOf<LoggingLevel | undefined>();
+    });
+});
diff --git a/scripts/smoke-dist-types.mjs b/scripts/smoke-dist-types.mjs
index 71584b92cc..e352d4c619 100644
--- a/scripts/smoke-dist-types.mjs
+++ b/scripts/smoke-dist-types.mjs
@@ -18,12 +18,16 @@ try {
             "import { AjvJsonSchemaValidator } from '@modelcontextprotocol/client/validators/ajv';",
             "import { CfWorkerJsonSchemaValidator as ClientCf } from '@modelcontextprotocol/client/validators/cf-worker';",
             "import { StdioClientTransport } from '@modelcontextprotocol/client/stdio';",
-            "import { McpServer } from '@modelcontextprotocol/server';",
+            "import { CLIENT_CAPABILITIES_META_KEY, McpServer } from '@modelcontextprotocol/server';",
+            "import type { ClientCapabilities, RequestMetaEnvelope } from '@modelcontextprotocol/server';",
             "import { AjvJsonSchemaValidator as ServerAjv } from '@modelcontextprotocol/server/validators/ajv';",
             "import { CfWorkerJsonSchemaValidator as ServerCf } from '@modelcontextprotocol/server/validators/cf-worker';",
             "import { StdioServerTransport } from '@modelcontextprotocol/server/stdio';",
             "export const c = new Client({ name: 'smoke', version: '1.0.0' });",
             "export const s = new McpServer({ name: 'smoke', version: '1.0.0' });",
+            'declare const envelope: Partial<RequestMetaEnvelope> | undefined;',
+            'const capabilities = envelope?.[CLIENT_CAPABILITIES_META_KEY];',
+            'export const _caps: ClientCapabilities | undefined = capabilities;',
             'export type T = ClientSchema;',
             'export { AjvJsonSchemaValidator, ServerAjv, ClientCf, ServerCf, StdioClientTransport, StdioServerTransport };',
             ''
@@ -77,10 +81,14 @@ try {
         [
             "import { Client } from '@modelcontextprotocol/client';",
             "import { StdioClientTransport } from '@modelcontextprotocol/client/stdio';",
-            "import { McpServer } from '@modelcontextprotocol/server';",
+            "import { CLIENT_CAPABILITIES_META_KEY, McpServer } from '@modelcontextprotocol/server';",
+            "import type { ClientCapabilities, RequestMetaEnvelope } from '@modelcontextprotocol/server';",
             "import { StdioServerTransport } from '@modelcontextprotocol/server/stdio';",
             "export const c = new Client({ name: 'smoke', version: '1.0.0' });",
             "export const s = new McpServer({ name: 'smoke', version: '1.0.0' });",
+            'declare const envelope: Partial<RequestMetaEnvelope> | undefined;',
+            'const capabilities = envelope?.[CLIENT_CAPABILITIES_META_KEY];',
+            'export const _caps: ClientCapabilities | undefined = capabilities;',
             'export { StdioClientTransport, StdioServerTransport };',
             ''
         ].join('\n')