Introduce implementation information to the initialize phase

docs/protocol/initialization.mdx

@@ -28,6 +28,8 @@ Before a Session can be created, Clients **MUST** initialize the connection by c
 - The latest [protocol version](#protocol-version) supported
 - The [capabilities](#client-capabilities) supported
 
+They **SHOULD** also provide a name and version to the Agent.
+
 ```json
 {
   "jsonrpc": "2.0",
@@ -41,12 +43,17 @@ Before a Session can be created, Clients **MUST** initialize the connection by c
         "writeTextFile": true
       },
       "terminal": true
+    },
+    "clientInfo": {
+      "name": "my-client",
+      "title": "My Client",
+      "version": "1.0.0"
     }
   }
 }
 ```
 
-The Agent **MUST** respond with the chosen [protocol version](#protocol-version) and the [capabilities](#agent-capabilities) it supports:
+The Agent **MUST** respond with the chosen [protocol version](#protocol-version) and the [capabilities](#agent-capabilities) it supports. It **SHOULD** also provide a name and version to the Client as well:
 
 ```json
 {
@@ -66,6 +73,11 @@ The Agent **MUST** respond with the chosen [protocol version](#protocol-version)
         "sse": true
       }
     },
+    "agentInfo": {
+      "name": "my-agent",
+      "title": "My Agent",
+      "version": "1.0.0"
+    },
     "authMethods": []
   }
 }
@@ -174,6 +186,29 @@ Note: This transport has been deprecated by the MCP spec.
 
 </ResponseField>
 
+## Implementation Information
+
+Both Clients and Agents **SHOULD** provide information about their implementation in the `clientInfo` and `agentInfo` fields respectively. Both take the following three fields:
+
+<ParamField path="name" type="string">
+  Intended for programmatic or logical use, but can be used as a display name
+  fallback if title isn’t present.
+</ParamField>
+
+<ParamField path="title" type="string">
+  Intended for UI and end-user contexts — optimized to be human-readable and
+  easily understood. If not provided, the name should be used for display.
+</ParamField>
+
+<ParamField path="version" type="string">
+  Version of the implementation. Can be displayed to the user or used for
+  debugging or metrics purposes.
+</ParamField>
+
+<Info>
+  Note: in future versions of the protocol, this information will be required.
+</Info>
+
 ---
 
 Once the connection is initialized, you're ready to [create a session](./session-setup) and begin the conversation with the Agent.

docs/protocol/schema.mdx

@@ -90,6 +90,12 @@ See protocol docs: [Initialization](https://agentclientprotocol.com/protocol/ini
 
     - Default: `{"fs":{"readTextFile":false,"writeTextFile":false},"terminal":false}`
 
+</ResponseField>
+<ResponseField name="clientInfo" type={<><span><a href="#implementation">Implementation</a></span><span> | null</span></>} >
+  Information about the Client name and version sent to the Agent.
+
+Note: in future versions of the protocol, this will be required.
+
 </ResponseField>
 <ResponseField name="protocolVersion" type={<a href="#protocolversion">ProtocolVersion</a>} required>
   The latest protocol version supported by the client.
@@ -115,6 +121,12 @@ See protocol docs: [Initialization](https://agentclientprotocol.com/protocol/ini
 
     - Default: `{"loadSession":false,"mcpCapabilities":{"http":false,"sse":false},"promptCapabilities":{"audio":false,"embeddedContext":false,"image":false}}`
 
+</ResponseField>
+<ResponseField name="agentInfo" type={<><span><a href="#implementation">Implementation</a></span><span> | null</span></>} >
+  Information about the Agent name and version sent to the Client.
+
+Note: in future versions of the protocol, this will be required.
+
 </ResponseField>
 <ResponseField name="authMethods" type={<><span><a href="#authmethod">AuthMethod</a></span><span>[]</span></>} >
   Authentication methods supported by the agent.
@@ -1491,6 +1503,31 @@ An HTTP header to set when making requests to the MCP server.
   The value to set for the HTTP header.
 </ResponseField>
 
+## <span class="font-mono">Implementation</span>
+
+Describes the name and version of an MCP implementation, with an optional
+title for UI representation.
+
+**Type:** Object
+
+**Properties:**
+
+<ResponseField name="name" type={"string"} required>
+  Intended for programmatic or logical use, but can be used as a display
+name fallback if title isn’t present.
+</ResponseField>
+<ResponseField name="title" type={"string | null"} >
+  Intended for UI and end-user contexts — optimized to be human-readable
+and easily understood.
+
+If not provided, the name should be used for display.
+
+</ResponseField>
+<ResponseField name="version" type={"string"} required>
+  Version of the implementation. Can be displayed to the user or used
+for debugging or metrics purposes.
+</ResponseField>
+
 ## <span class="font-mono">McpCapabilities</span>
 
 MCP capabilities supported by the agent

docs/v2-changes.md

@@ -0,0 +1,9 @@
+# Proposal for changes in an ACP v2
+
+A WIP document to keep track of ideas and proposals for breaking changes that would require a version bump in the protocol.
+
+## Proposed Changes
+
+- Make `clientInfo` and `agentInfo` required in the `initialize` request.
+
+## Agreed on Changes

rust/agent.rs

@@ -29,6 +29,11 @@ pub struct InitializeRequest {
     /// Capabilities supported by the client.
     #[serde(default)]
     pub client_capabilities: ClientCapabilities,
+    /// Information about the Client name and version sent to the Agent.
+    ///
+    /// Note: in future versions of the protocol, this will be required.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub client_info: Option<Implementation>,
     /// Extension point for implementations
     #[serde(skip_serializing_if = "Option::is_none", rename = "_meta")]
     pub meta: Option<serde_json::Value>,
@@ -54,11 +59,34 @@ pub struct InitializeResponse {
     /// Authentication methods supported by the agent.
     #[serde(default)]
     pub auth_methods: Vec<AuthMethod>,
+    /// Information about the Agent name and version sent to the Client.
+    ///
+    /// Note: in future versions of the protocol, this will be required.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub agent_info: Option<Implementation>,
     /// Extension point for implementations
     #[serde(skip_serializing_if = "Option::is_none", rename = "_meta")]
     pub meta: Option<serde_json::Value>,
 }
 
+/// Describes the name and version of an MCP implementation, with an optional
+/// title for UI representation.
+#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+#[serde(rename_all = "camelCase")]
+pub struct Implementation {
+    /// Intended for programmatic or logical use, but can be used as a display
+    /// name fallback if title isn’t present.
+    name: String,
+    /// Intended for UI and end-user contexts — optimized to be human-readable
+    /// and easily understood.
+    ///
+    /// If not provided, the name should be used for display.
+    title: Option<String>,
+    /// Version of the implementation. Can be displayed to the user or used
+    /// for debugging or metrics purposes.
+    version: String,
+}
+
 // Authentication
 
 /// Request parameters for the authenticate method.

rust/bin/generate.rs

@@ -17,7 +17,7 @@ struct AgentOutgoingMessage(JsonRpcMessage<OutgoingMessage<AgentSide, ClientSide
 #[schemars(extend("x-docs-ignore" = true))]
 struct ClientOutgoingMessage(JsonRpcMessage<OutgoingMessage<ClientSide, AgentSide>>);
 
-#[expect(dead_code, clippy::large_enum_variant)]
+#[expect(dead_code)]
 #[derive(JsonSchema)]
 #[serde(untagged)]
 enum AcpTypes {

schema/schema.json

@@ -958,6 +958,25 @@
       "required": ["name", "value"],
       "type": "object"
     },
+    "Implementation": {
+      "description": "Describes the name and version of an MCP implementation, with an optional\ntitle for UI representation.",
+      "properties": {
+        "name": {
+          "description": "Intended for programmatic or logical use, but can be used as a display\nname fallback if title isn’t present.",
+          "type": "string"
+        },
+        "title": {
+          "description": "Intended for UI and end-user contexts — optimized to be human-readable\nand easily understood.\n\nIf not provided, the name should be used for display.",
+          "type": ["string", "null"]
+        },
+        "version": {
+          "description": "Version of the implementation. Can be displayed to the user or used\nfor debugging or metrics purposes.",
+          "type": "string"
+        }
+      },
+      "required": ["name", "version"],
+      "type": "object"
+    },
     "InitializeRequest": {
       "description": "Request parameters for the initialize method.\n\nSent by the client to establish connection and negotiate capabilities.\n\nSee protocol docs: [Initialization](https://agentclientprotocol.com/protocol/initialization)",
       "properties": {
@@ -975,6 +994,17 @@
           },
           "description": "Capabilities supported by the client."
         },
+        "clientInfo": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/Implementation"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "description": "Information about the Client name and version sent to the Agent.\n\nNote: in future versions of the protocol, this will be required."
+        },
         "protocolVersion": {
           "$ref": "#/$defs/ProtocolVersion",
           "description": "The latest protocol version supported by the client."
@@ -1007,6 +1037,17 @@
           },
           "description": "Capabilities supported by the agent."
         },
+        "agentInfo": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/Implementation"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "description": "Information about the Agent name and version sent to the Client.\n\nNote: in future versions of the protocol, this will be required."
+        },
         "authMethods": {
           "default": [],
           "description": "Authentication methods supported by the agent.",