microsoft · DonJayamanne · Jun 3, 2026 · Jun 3, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -31,6 +31,7 @@ Spec version: `0.3.0`
   `changeset/operationStatusChanged` action so servers can reflect an
   operation's execution lifecycle (`idle → running → error`) back into
   changeset state.
+- Added optional `_meta` provider metadata to `AgentCustomization`.
 - Renamed the `UserMessage` type to `Message` and surfaced it consistently
   across turn state (`Turn.message`, `ActiveTurn.message`, `PendingMessage.message`)
   and the actions that carry it (`session/turnStarted`,

diff --git a/clients/go/CHANGELOG.md b/clients/go/CHANGELOG.md
@@ -15,9 +15,11 @@ tag whose matching `## [X.Y.Z]` heading is missing from this file.
 ## [Unreleased]
 
 ### Added
+
 - `status` and `error` fields on `ChangesetOperation` and the
   `changeset/operationStatusChanged` action, tracking the
   `idle → running → error` lifecycle of a changeset operation.
+- `AgentCustomization._meta` provider metadata field.
 
 ## [0.1.0] — 2026-05-28
 

diff --git a/clients/go/ahptypes/state.generated.go b/clients/go/ahptypes/state.generated.go
@@ -1696,6 +1696,10 @@ type AgentCustomization struct {
 	// Short description of what the agent specializes in and when to
 	// invoke it. Sourced from the agent file's frontmatter `description`.
 	Description *string `json:"description,omitempty"`
+	// Additional provider-specific metadata for this custom agent.
+	//
+	// Mirrors the MCP `_meta` convention.
+	Meta map[string]json.RawMessage `json:"_meta,omitempty"`
 }
 
 // A skill contributed by a plugin or directory.

diff --git a/clients/kotlin/CHANGELOG.md b/clients/kotlin/CHANGELOG.md
@@ -16,9 +16,11 @@ versions (`*-SNAPSHOT`) are explicitly rejected by the publish pipeline; bump
 ## [Unreleased]
 
 ### Added
+
 - `status` and `error` fields on `ChangesetOperation` and the
   `changeset/operationStatusChanged` action, tracking the
   `idle → running → error` lifecycle of a changeset operation.
+- `AgentCustomization._meta` provider metadata field.
 
 ## [0.2.0] — 2026-05-28
 

diff --git a/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt b/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt
@@ -2481,7 +2481,14 @@ data class AgentCustomization(
      * Short description of what the agent specializes in and when to
      * invoke it. Sourced from the agent file's frontmatter `description`.
      */
-    val description: String? = null
+    val description: String? = null,
+    /**
+     * Additional provider-specific metadata for this custom agent.
+     * 
+     * Mirrors the MCP `_meta` convention.
+     */
+    @SerialName("_meta")
+    val meta: Map<String, JsonElement>? = null
 )
 
 @Serializable

diff --git a/clients/rust/CHANGELOG.md b/clients/rust/CHANGELOG.md
@@ -16,9 +16,11 @@ matching `## [X.Y.Z]` heading is missing from this file.
 ## [Unreleased]
 
 ### Added
+
 - `status` and `error` fields on `ChangesetOperation` and the
   `changeset/operationStatusChanged` action, tracking the
   `idle → running → error` lifecycle of a changeset operation.
+- `AgentCustomization._meta` provider metadata field.
 
 ## [0.2.0] — 2026-05-28
 

diff --git a/clients/rust/crates/ahp-types/src/state.rs b/clients/rust/crates/ahp-types/src/state.rs
@@ -2075,6 +2075,11 @@ pub struct AgentCustomization {
     /// invoke it. Sourced from the agent file's frontmatter `description`.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub description: Option<String>,
+    /// Additional provider-specific metadata for this custom agent.
+    ///
+    /// Mirrors the MCP `_meta` convention.
+    #[serde(rename = "_meta", default, skip_serializing_if = "Option::is_none")]
+    pub meta: Option<JsonObject>,
 }
 
 /// A skill contributed by a plugin or directory.

diff --git a/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift b/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift
@@ -2665,6 +2665,21 @@ public struct AgentCustomization: Codable, Sendable {
     /// Short description of what the agent specializes in and when to
     /// invoke it. Sourced from the agent file's frontmatter `description`.
     public var description: String?
+    /// Additional provider-specific metadata for this custom agent.
+    /// 
+    /// Mirrors the MCP `_meta` convention.
+    public var meta: [String: AnyCodable]?
+
+    enum CodingKeys: String, CodingKey {
+        case id
+        case uri
+        case name
+        case icons
+        case range
+        case type
+        case description
+        case meta = "_meta"
+    }
 
     public init(
         id: String,
@@ -2673,7 +2688,8 @@ public struct AgentCustomization: Codable, Sendable {
         icons: [Icon]? = nil,
         range: TextRange? = nil,
         type: CustomizationType,
-        description: String? = nil
+        description: String? = nil,
+        meta: [String: AnyCodable]? = nil
     ) {
         self.id = id
         self.uri = uri
@@ -2682,6 +2698,7 @@ public struct AgentCustomization: Codable, Sendable {
         self.range = range
         self.type = type
         self.description = description
+        self.meta = meta
     }
 }
 

diff --git a/clients/swift/CHANGELOG.md b/clients/swift/CHANGELOG.md
@@ -18,9 +18,11 @@ the tag matches the version pinned in [`VERSION`](VERSION).
 ## [Unreleased]
 
 ### Added
+
 - `status` and `error` fields on `ChangesetOperation` and the
   `changeset/operationStatusChanged` action, tracking the
   `idle → running → error` lifecycle of a changeset operation.
+- `AgentCustomization._meta` provider metadata field.
 
 ## [0.2.0] — 2026-05-28
 

diff --git a/clients/typescript/CHANGELOG.md b/clients/typescript/CHANGELOG.md
@@ -21,9 +21,11 @@ hotfix escape hatch.
 ## [Unreleased]
 
 ### Added
+
 - `status` and `error` fields on `ChangesetOperation` and the
   `changeset/operationStatusChanged` action, tracking the
   `idle → running → error` lifecycle of a changeset operation.
+- `AgentCustomization._meta` provider metadata field.
 
 ## [0.2.0] — 2026-05-28
 

diff --git a/schema/actions.schema.json b/schema/actions.schema.json
@@ -4431,6 +4431,11 @@
         "description": {
           "type": "string",
           "description": "Short description of what the agent specializes in and when to\ninvoke it. Sourced from the agent file's frontmatter `description`."
+        },
+        "_meta": {
+          "type": "object",
+          "additionalProperties": {},
+          "description": "Additional provider-specific metadata for this custom agent.\n\nMirrors the MCP `_meta` convention."
         }
       },
       "required": [

diff --git a/schema/commands.schema.json b/schema/commands.schema.json
@@ -4082,6 +4082,11 @@
         "description": {
           "type": "string",
           "description": "Short description of what the agent specializes in and when to\ninvoke it. Sourced from the agent file's frontmatter `description`."
+        },
+        "_meta": {
+          "type": "object",
+          "additionalProperties": {},
+          "description": "Additional provider-specific metadata for this custom agent.\n\nMirrors the MCP `_meta` convention."
         }
       },
       "required": [

diff --git a/schema/errors.schema.json b/schema/errors.schema.json
@@ -3014,6 +3014,11 @@
         "description": {
           "type": "string",
           "description": "Short description of what the agent specializes in and when to\ninvoke it. Sourced from the agent file's frontmatter `description`."
+        },
+        "_meta": {
+          "type": "object",
+          "additionalProperties": {},
+          "description": "Additional provider-specific metadata for this custom agent.\n\nMirrors the MCP `_meta` convention."
         }
       },
       "required": [

diff --git a/schema/notifications.schema.json b/schema/notifications.schema.json
@@ -3142,6 +3142,11 @@
         "description": {
           "type": "string",
           "description": "Short description of what the agent specializes in and when to\ninvoke it. Sourced from the agent file's frontmatter `description`."
+        },
+        "_meta": {
+          "type": "object",
+          "additionalProperties": {},
+          "description": "Additional provider-specific metadata for this custom agent.\n\nMirrors the MCP `_meta` convention."
         }
       },
       "required": [

diff --git a/schema/state.schema.json b/schema/state.schema.json
@@ -2925,6 +2925,11 @@
         "description": {
           "type": "string",
           "description": "Short description of what the agent specializes in and when to\ninvoke it. Sourced from the agent file's frontmatter `description`."
+        },
+        "_meta": {
+          "type": "object",
+          "additionalProperties": {},
+          "description": "Additional provider-specific metadata for this custom agent.\n\nMirrors the MCP `_meta` convention."
         }
       },
       "required": [

diff --git a/types/channels-session/state.ts b/types/channels-session/state.ts
@@ -1525,6 +1525,12 @@ export interface AgentCustomization extends CustomizationBase {
    * invoke it. Sourced from the agent file's frontmatter `description`.
    */
   description?: string;
+  /**
+   * Additional provider-specific metadata for this custom agent.
+   *
+   * Mirrors the MCP `_meta` convention.
+   */
+  _meta?: Record<string, unknown>;
 }
 
 /**