diff --git a/schema/draft/schema.json b/schema/draft/schema.json
index f1139948d..5d866c53e 100644
--- a/schema/draft/schema.json
+++ b/schema/draft/schema.json
@@ -27,6 +27,11 @@
         "AudioContent": {
             "description": "Audio provided to or from an LLM.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -54,6 +59,11 @@
         },
         "BlobResourceContents": {
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "blob": {
                     "description": "A base64-encoded string representing the binary data of the item.",
                     "format": "byte",
@@ -616,6 +626,11 @@
         "EmbeddedResource": {
             "description": "The contents of a resource, embedded into a prompt or tool call result.\n\nIt is up to the client how best to render embedded resources for the benefit\nof the LLM and/or the user.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -735,6 +750,11 @@
         "ImageContent": {
             "description": "An image provided to or from an LLM.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -964,6 +984,7 @@
                     "additionalProperties": {},
                     "properties": {
                         "_meta": {
+                            "additionalProperties": {},
                             "properties": {
                                 "progressToken": {
                                     "$ref": "#/definitions/ProgressToken",
@@ -1153,6 +1174,7 @@
                     "additionalProperties": {},
                     "properties": {
                         "_meta": {
+                            "additionalProperties": {},
                             "properties": {
                                 "progressToken": {
                                     "$ref": "#/definitions/ProgressToken",
@@ -1419,6 +1441,7 @@
                     "additionalProperties": {},
                     "properties": {
                         "_meta": {
+                            "additionalProperties": {},
                             "properties": {
                                 "progressToken": {
                                     "$ref": "#/definitions/ProgressToken",
@@ -1502,6 +1525,11 @@
         "Prompt": {
             "description": "A prompt or prompt template that the server offers.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "arguments": {
                     "description": "A list of arguments to use for templating the prompt.",
                     "items": {
@@ -1665,6 +1693,7 @@
                     "additionalProperties": {},
                     "properties": {
                         "_meta": {
+                            "additionalProperties": {},
                             "properties": {
                                 "progressToken": {
                                     "$ref": "#/definitions/ProgressToken",
@@ -1692,6 +1721,11 @@
         "Resource": {
             "description": "A known resource that the server is capable of reading.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -1727,6 +1761,11 @@
         "ResourceContents": {
             "description": "The contents of a specific resource or sub-resource.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "mimeType": {
                     "description": "The MIME type of this resource, if known.",
                     "type": "string"
@@ -1745,6 +1784,11 @@
         "ResourceLink": {
             "description": "A resource that the server is capable of reading, included in a prompt or tool call result.\n\nNote: resource links returned by tools are not guaranteed to appear in the results of `resources/list` requests.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -1809,6 +1853,11 @@
         "ResourceTemplate": {
             "description": "A template description for resources available on the server.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -1905,6 +1954,11 @@
         "Root": {
             "description": "Represents a root directory or file that the server can operate on.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "name": {
                     "description": "An optional name for the root. This can be used to provide a human-readable\nidentifier for the root, which may be useful for display purposes or for\nreferencing the root in other parts of the application.",
                     "type": "string"
@@ -2195,6 +2249,11 @@
         "TextContent": {
             "description": "Text provided to or from an LLM.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/Annotations",
                     "description": "Optional annotations for the client."
@@ -2216,6 +2275,11 @@
         },
         "TextResourceContents": {
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "mimeType": {
                     "description": "The MIME type of this resource, if known.",
                     "type": "string"
@@ -2239,6 +2303,11 @@
         "Tool": {
             "description": "Definition for a tool the client can call.",
             "properties": {
+                "_meta": {
+                    "additionalProperties": {},
+                    "description": "Reserved field for additional metadata.",
+                    "type": "object"
+                },
                 "annotations": {
                     "$ref": "#/definitions/ToolAnnotations",
                     "description": "Optional additional tool information."
diff --git a/schema/draft/schema.ts b/schema/draft/schema.ts
index fdbb02894..5b9ae8a39 100644
--- a/schema/draft/schema.ts
+++ b/schema/draft/schema.ts
@@ -30,6 +30,7 @@ export interface Request {
        * If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
        */
       progressToken?: ProgressToken;
+      [key: string]: unknown;
     };
     [key: string]: unknown;
   };
@@ -472,6 +473,11 @@ export interface Resource {
    * This can be used by Hosts to display file sizes and estimate context window usage.
    */
   size?: number;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -508,6 +514,11 @@ export interface ResourceTemplate {
    * Optional annotations for the client.
    */
   annotations?: Annotations;
+  
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -524,6 +535,11 @@ export interface ResourceContents {
    * The MIME type of this resource, if known.
    */
   mimeType?: string;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 export interface TextResourceContents extends ResourceContents {
@@ -601,6 +617,11 @@ export interface Prompt {
    * A list of arguments to use for templating the prompt.
    */
   arguments?: PromptArgument[];
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -660,6 +681,11 @@ export interface EmbeddedResource {
    * Optional annotations for the client.
    */
   annotations?: Annotations;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 /**
  * An optional notification from the server to the client, informing it that the list of prompts it offers has changed. This may be issued by servers without any previous subscription from the client.
@@ -825,6 +851,11 @@ export interface Tool {
    * Optional additional tool information.
    */
   annotations?: ToolAnnotations;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /* Logging */
@@ -994,6 +1025,11 @@ export interface TextContent {
    * Optional annotations for the client.
    */
   annotations?: Annotations;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -1018,6 +1054,11 @@ export interface ImageContent {
    * Optional annotations for the client.
    */
   annotations?: Annotations;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -1042,6 +1083,11 @@ export interface AudioContent {
    * Optional annotations for the client.
    */
   annotations?: Annotations;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**
@@ -1243,6 +1289,11 @@ export interface Root {
    * referencing the root in other parts of the application.
    */
   name?: string;
+
+  /**
+   * Reserved field for additional metadata.
+   */
+  _meta?: { [key: string]: unknown };
 }
 
 /**