diff --git a/core/src/Microsoft.Bot.Core/Activities/Activity.cs b/core/src/Microsoft.Bot.Core/Activities/Activity.cs
new file mode 100644
index 00000000..4c5931ed
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/Activity.cs
@@ -0,0 +1,325 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Base class for bot activities.
+/// </summary>
+#pragma warning disable CA1056 // URI properties should not be strings
+public class Activity
+#pragma warning restore CA1056 // URI properties should not be strings
+{
+    /// <summary>
+    /// Gets or sets the unique identifier for the activity.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the type of the activity.
+    /// </summary>
+    [JsonPropertyName("type")]
+    public string? Type { get; set; }
+
+    /// <summary>
+    /// Gets or sets the ID of the activity to which this activity is a reply.
+    /// </summary>
+    [JsonPropertyName("replyToId")]
+    public string? ReplyToId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the channel identifier.
+    /// </summary>
+    [JsonPropertyName("channelId")]
+    public string? ChannelId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the account that sent this activity.
+    /// </summary>
+    [JsonPropertyName("from")]
+    public Account? From { get; set; }
+
+    /// <summary>
+    /// Gets or sets the account that should receive this activity.
+    /// </summary>
+    [JsonPropertyName("recipient")]
+    public Account? Recipient { get; set; }
+
+    /// <summary>
+    /// Gets or sets the conversation in which this activity is taking place.
+    /// </summary>
+    [JsonPropertyName("conversation")]
+    public Conversation? Conversation { get; set; }
+
+    /// <summary>
+    /// Gets or sets a reference to another conversation or activity.
+    /// </summary>
+    [JsonPropertyName("relatesTo")]
+    public ConversationReference? RelatesTo { get; set; }
+
+    /// <summary>
+    /// Gets or sets the URL of the service endpoint.
+    /// </summary>
+    [JsonPropertyName("serviceUrl")]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1056:URI properties should not be strings", Justification = "Activity schema uses string for ServiceUrl")]
+    public string? ServiceUrl { get; set; }
+
+    /// <summary>
+    /// Gets or sets the locale of the activity.
+    /// </summary>
+    [JsonPropertyName("locale")]
+    public string? Locale { get; set; }
+
+    /// <summary>
+    /// Gets or sets the timestamp of when the activity was sent.
+    /// </summary>
+    [JsonPropertyName("timestamp")]
+    public DateTime? Timestamp { get; set; }
+
+    /// <summary>
+    /// Gets or sets the local timestamp of when the activity was sent.
+    /// </summary>
+    [JsonPropertyName("localTimestamp")]
+    public DateTime? LocalTimestamp { get; set; }
+
+    /// <summary>
+    /// Gets the collection of entities included in the activity.
+    /// </summary>
+    [JsonPropertyName("entities")]
+    public IList<Entity>? Entities { get; init; }
+
+    /// <summary>
+    /// Gets or sets channel-specific data associated with this activity.
+    /// </summary>
+    [JsonPropertyName("channelData")]
+    public ChannelData? ChannelData { get; set; }
+
+    /// <summary>
+    /// Gets or sets extension data for additional properties.
+    /// </summary>
+    [JsonExtensionData]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Usage", "CA2227:Collection properties should be read only", Justification = "JsonExtensionData requires a setter")]
+    public IDictionary<string, object?>? Properties { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Activity"/> class.
+    /// </summary>
+    public Activity()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Activity"/> class with the specified type.
+    /// </summary>
+    /// <param name="type">The activity type.</param>
+    public Activity(string type)
+    {
+        Type = type;
+    }
+}
+
+/// <summary>
+/// Represents an account.
+/// </summary>
+#pragma warning disable CA1724 // Type names should not match namespaces
+public class Account
+#pragma warning restore CA1724 // Type names should not match namespaces
+{
+    /// <summary>
+    /// Gets or sets the unique identifier for the account.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the Azure Active Directory object ID.
+    /// </summary>
+    [JsonPropertyName("aadObjectId")]
+    public string? AadObjectId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the role of the account. See <see cref="Roles"/> for common values.
+    /// </summary>
+    [JsonPropertyName("role")]
+    public string? Role { get; set; }
+
+    /// <summary>
+    /// Gets or sets the name of the account.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets additional properties.
+    /// </summary>
+    [JsonPropertyName("properties")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public Dictionary<string, object>? Properties { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
+
+/// <summary>
+/// String constants for account roles.
+/// </summary>
+public static class Roles
+{
+    /// <summary>
+    /// Indicates the account is a bot.
+    /// </summary>
+    public const string Bot = "bot";
+
+    /// <summary>
+    /// Indicates the account is a user.
+    /// </summary>
+    public const string User = "user";
+}
+
+/// <summary>
+/// Represents a conversation.
+/// </summary>
+public class Conversation
+{
+    /// <summary>
+    /// Gets or sets the unique identifier for the conversation.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the name of the conversation.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets additional properties.
+    /// </summary>
+    [JsonPropertyName("properties")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public Dictionary<string, object>? Properties { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
+
+/// <summary>
+/// Represents a reference to another conversation or activity.
+/// </summary>
+#pragma warning disable CA1056 // URI properties should not be strings
+public class ConversationReference
+#pragma warning restore CA1056 // URI properties should not be strings
+{
+    /// <summary>
+    /// Gets or sets the activity ID.
+    /// </summary>
+    [JsonPropertyName("activityId")]
+    public string? ActivityId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the user account.
+    /// </summary>
+    [JsonPropertyName("user")]
+    public Account? User { get; set; }
+
+    /// <summary>
+    /// Gets or sets the bot account.
+    /// </summary>
+    [JsonPropertyName("bot")]
+    public Account? Bot { get; set; }
+
+    /// <summary>
+    /// Gets or sets the conversation.
+    /// </summary>
+    [JsonPropertyName("conversation")]
+    public Conversation? Conversation { get; set; }
+
+    /// <summary>
+    /// Gets or sets the channel ID.
+    /// </summary>
+    [JsonPropertyName("channelId")]
+    public string? ChannelId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the service URL.
+    /// </summary>
+    [JsonPropertyName("serviceUrl")]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1056:URI properties should not be strings", Justification = "Activity schema uses string for ServiceUrl")]
+    public string? ServiceUrl { get; set; }
+}
+
+/// <summary>
+/// Represents channel-specific data.
+/// </summary>
+public class ChannelData
+{
+    /// <summary>
+    /// Gets or sets extension data for additional properties.
+    /// </summary>
+    [JsonExtensionData]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IDictionary<string, object?>? Properties { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
+
+/// <summary>
+/// Represents an entity.
+/// </summary>
+public class Entity
+{
+    /// <summary>
+    /// Gets or sets the type of the entity.
+    /// </summary>
+    [JsonPropertyName("type")]
+    public string? Type { get; set; }
+
+    /// <summary>
+    /// Gets or sets extension data for additional properties.
+    /// </summary>
+    [JsonExtensionData]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IDictionary<string, object?>? Properties { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
+
+/// <summary>
+/// Represents an error.
+/// </summary>
+#pragma warning disable CA1716 // Identifiers should not match keywords
+public class Error
+#pragma warning restore CA1716 // Identifiers should not match keywords
+{
+    /// <summary>
+    /// Gets or sets the error code.
+    /// </summary>
+    [JsonPropertyName("code")]
+    public string? Code { get; set; }
+
+    /// <summary>
+    /// Gets or sets the error message.
+    /// </summary>
+    [JsonPropertyName("message")]
+    public string? Message { get; set; }
+
+    /// <summary>
+    /// Gets or sets inner HTTP error details.
+    /// </summary>
+    [JsonPropertyName("innerHttpError")]
+    public InnerHttpError? InnerHttpError { get; set; }
+}
+
+/// <summary>
+/// Represents inner HTTP error details.
+/// </summary>
+public class InnerHttpError
+{
+    /// <summary>
+    /// Gets or sets the HTTP status code.
+    /// </summary>
+    [JsonPropertyName("statusCode")]
+    public int? StatusCode { get; set; }
+
+    /// <summary>
+    /// Gets or sets the response body.
+    /// </summary>
+    [JsonPropertyName("body")]
+    public object? Body { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/ActivityTypes.cs b/core/src/Microsoft.Bot.Core/Activities/ActivityTypes.cs
new file mode 100644
index 00000000..5a941a60
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/ActivityTypes.cs
@@ -0,0 +1,70 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// String constants for activity types.
+/// </summary>
+public static class ActivityTypes
+{
+    /// <summary>
+    /// Message activity type.
+    /// </summary>
+    public const string Message = "message";
+
+    /// <summary>
+    /// Typing activity type.
+    /// </summary>
+    public const string Typing = "typing";
+
+    /// <summary>
+    /// Event activity type.
+    /// </summary>
+    public const string Event = "event";
+
+    /// <summary>
+    /// Command activity type.
+    /// </summary>
+    public const string Command = "command";
+
+    /// <summary>
+    /// Command result activity type.
+    /// </summary>
+    public const string CommandResult = "commandResult";
+
+    /// <summary>
+    /// Installation update activity type.
+    /// </summary>
+    public const string InstallationUpdate = "installationUpdate";
+
+    /// <summary>
+    /// Conversation update activity type.
+    /// </summary>
+    public const string ConversationUpdate = "conversationUpdate";
+
+    /// <summary>
+    /// End of conversation activity type.
+    /// </summary>
+    public const string EndOfConversation = "endOfConversation";
+
+    /// <summary>
+    /// Invoke activity type.
+    /// </summary>
+    public const string Invoke = "invoke";
+
+    /// <summary>
+    /// Message delete activity type.
+    /// </summary>
+    public const string MessageDelete = "messageDelete";
+
+    /// <summary>
+    /// Message update activity type.
+    /// </summary>
+    public const string MessageUpdate = "messageUpdate";
+
+    /// <summary>
+    /// Message reaction activity type.
+    /// </summary>
+    public const string MessageReaction = "messageReaction";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/AdaptiveCardActivity.cs b/core/src/Microsoft.Bot.Core/Activities/AdaptiveCardActivity.cs
new file mode 100644
index 00000000..d8954d40
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/AdaptiveCardActivity.cs
@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an adaptive card invoke activity.
+/// </summary>
+public class AdaptiveCardActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AdaptiveCardActivity"/> class.
+    /// </summary>
+    public AdaptiveCardActivity()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AdaptiveCardActivity"/> class with the specified name.
+    /// </summary>
+    /// <param name="name">The invoke operation name.</param>
+    public AdaptiveCardActivity(string name)
+    {
+        Name = name;
+    }
+}
+
+/// <summary>
+/// Represents an adaptive card action invoke activity.
+/// </summary>
+public class AdaptiveCardActionActivity : AdaptiveCardActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AdaptiveCardActionActivity"/> class.
+    /// </summary>
+    public AdaptiveCardActionActivity() : base("adaptiveCard/action")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/CommandActivity.cs b/core/src/Microsoft.Bot.Core/Activities/CommandActivity.cs
new file mode 100644
index 00000000..fd290ca2
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/CommandActivity.cs
@@ -0,0 +1,49 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a command activity.
+/// </summary>
+public class CommandActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the name of the command.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets the value for this command.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public CommandValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CommandActivity"/> class.
+    /// </summary>
+    public CommandActivity() : base(ActivityTypes.Command)
+    {
+    }
+}
+
+/// <summary>
+/// The value field of a command activity contains metadata related to a command.
+/// An optional extensible data payload may be included if defined by the command activity name.
+/// </summary>
+public class CommandValue
+{
+    /// <summary>
+    /// Gets or sets the channel ID for the command.
+    /// </summary>
+    [JsonPropertyName("channelId")]
+    public string? ChannelId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the data field containing optional parameters specific to this command activity,
+    /// as defined by the name. The value of the data field is a complex type.
+    /// </summary>
+    [JsonPropertyName("data")]
+    public object? Data { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/CommandResultActivity.cs b/core/src/Microsoft.Bot.Core/Activities/CommandResultActivity.cs
new file mode 100644
index 00000000..29a1e16c
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/CommandResultActivity.cs
@@ -0,0 +1,56 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Asynchronous external command result activity.
+/// </summary>
+public class CommandResultActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the name of the command.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets the value for this command result.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public CommandResultValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CommandResultActivity"/> class.
+    /// </summary>
+    public CommandResultActivity() : base(ActivityTypes.CommandResult)
+    {
+    }
+}
+
+/// <summary>
+/// The value field of a <see cref="CommandResultActivity"/> contains metadata related to a command result.
+/// An optional extensible data payload may be included if defined by the command result activity name. 
+/// The presence of an error field indicates that the original command failed to complete.
+/// </summary>
+public class CommandResultValue
+{
+    /// <summary>
+    /// Gets or sets the ID of the command.
+    /// </summary>
+    [JsonPropertyName("commandId")]
+    public string? CommandId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the data field containing optional parameters specific to this command result activity,
+    /// as defined by the name. The value of the data field is a complex type.
+    /// </summary>
+    [JsonPropertyName("data")]
+    public object? Data { get; set; }
+
+    /// <summary>
+    /// Gets or sets the optional error, if the command result indicates a failure.
+    /// </summary>
+    [JsonPropertyName("error")]
+    public Error? Error { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/ConfigActivity.cs b/core/src/Microsoft.Bot.Core/Activities/ConfigActivity.cs
new file mode 100644
index 00000000..c5d3ee52
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/ConfigActivity.cs
@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a config fetch invoke activity.
+/// </summary>
+public class ConfigFetchActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConfigFetchActivity"/> class.
+    /// </summary>
+    public ConfigFetchActivity() : base("config/fetch")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a config submit invoke activity.
+/// </summary>
+public class ConfigSubmitActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConfigSubmitActivity"/> class.
+    /// </summary>
+    public ConfigSubmitActivity() : base("config/submit")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/ConversationUpdateActivity.cs b/core/src/Microsoft.Bot.Core/Activities/ConversationUpdateActivity.cs
new file mode 100644
index 00000000..eee2e3e7
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/ConversationUpdateActivity.cs
@@ -0,0 +1,121 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a conversation update activity.
+/// </summary>
+public class ConversationUpdateActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the updated topic name of the conversation.
+    /// </summary>
+    [JsonPropertyName("topicName")]
+    public string? TopicName { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether the prior history of the channel is disclosed.
+    /// </summary>
+    [JsonPropertyName("historyDisclosed")]
+    public bool? HistoryDisclosed { get; set; }
+
+    /// <summary>
+    /// Gets or sets the collection of members added to the conversation.
+    /// </summary>
+    [JsonPropertyName("membersAdded")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<Account>? MembersAdded { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+
+    /// <summary>
+    /// Gets or sets the collection of members removed from the conversation.
+    /// </summary>
+    [JsonPropertyName("membersRemoved")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<Account>? MembersRemoved { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConversationUpdateActivity"/> class.
+    /// </summary>
+    public ConversationUpdateActivity() : base(ActivityTypes.ConversationUpdate)
+    {
+    }
+}
+
+/// <summary>
+/// String constants for conversation update event types.
+/// </summary>
+public static class ConversationEventTypes
+{
+    /// <summary>
+    /// Channel created event type.
+    /// </summary>
+    public const string ChannelCreated = "channelCreated";
+
+    /// <summary>
+    /// Channel deleted event type.
+    /// </summary>
+    public const string ChannelDeleted = "channelDeleted";
+
+    /// <summary>
+    /// Channel renamed event type.
+    /// </summary>
+    public const string ChannelRenamed = "channelRenamed";
+
+    /// <summary>
+    /// Channel restored event type.
+    /// </summary>
+    public const string ChannelRestored = "channelRestored";
+
+    /// <summary>
+    /// Channel shared event type.
+    /// </summary>
+    public const string ChannelShared = "channelShared";
+
+    /// <summary>
+    /// Channel unshared event type.
+    /// </summary>
+    public const string ChannelUnShared = "channelUnshared";
+
+    /// <summary>
+    /// Channel member added event type.
+    /// </summary>
+    public const string ChannelMemberAdded = "channelMemberAdded";
+
+    /// <summary>
+    /// Channel member removed event type.
+    /// </summary>
+    public const string ChannelMemberRemoved = "channelMemberRemoved";
+
+    /// <summary>
+    /// Team archived event type.
+    /// </summary>
+    public const string TeamArchived = "teamArchived";
+
+    /// <summary>
+    /// Team deleted event type.
+    /// </summary>
+    public const string TeamDeleted = "teamDeleted";
+
+    /// <summary>
+    /// Team hard deleted event type.
+    /// </summary>
+    public const string TeamHardDeleted = "teamHardDeleted";
+
+    /// <summary>
+    /// Team renamed event type.
+    /// </summary>
+    public const string TeamRenamed = "teamRenamed";
+
+    /// <summary>
+    /// Team restored event type.
+    /// </summary>
+    public const string TeamRestored = "teamRestored";
+
+    /// <summary>
+    /// Team unarchived event type.
+    /// </summary>
+    public const string TeamUnarchived = "teamUnarchived";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/EndOfConversationActivity.cs b/core/src/Microsoft.Bot.Core/Activities/EndOfConversationActivity.cs
new file mode 100644
index 00000000..d3f3d4e2
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/EndOfConversationActivity.cs
@@ -0,0 +1,66 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an end of conversation activity.
+/// </summary>
+public class EndOfConversationActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the code for endOfConversation activities that indicates why the conversation ended.
+    /// See <see cref="EndOfConversationCodes"/> for common values.
+    /// </summary>
+    [JsonPropertyName("code")]
+    public string? Code { get; set; }
+
+    /// <summary>
+    /// Gets or sets the text content of the message.
+    /// </summary>
+    [JsonPropertyName("text")]
+    public string? Text { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="EndOfConversationActivity"/> class.
+    /// </summary>
+    public EndOfConversationActivity() : base(ActivityTypes.EndOfConversation)
+    {
+    }
+}
+
+/// <summary>
+/// String constants for end of conversation codes.
+/// </summary>
+public static class EndOfConversationCodes
+{
+    /// <summary>
+    /// Unknown reason for ending the conversation.
+    /// </summary>
+    public const string Unknown = "unknown";
+
+    /// <summary>
+    /// Conversation completed successfully.
+    /// </summary>
+    public const string CompletedSuccessfully = "completedSuccessfully";
+
+    /// <summary>
+    /// User cancelled the conversation.
+    /// </summary>
+    public const string UserCancelled = "userCancelled";
+
+    /// <summary>
+    /// Bot timed out.
+    /// </summary>
+    public const string BotTimedOut = "botTimedOut";
+
+    /// <summary>
+    /// Bot issued an invalid message.
+    /// </summary>
+    public const string BotIssuedInvalidMessage = "botIssuedInvalidMessage";
+
+    /// <summary>
+    /// Channel failed.
+    /// </summary>
+    public const string ChannelFailed = "channelFailed";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/EventActivity.cs b/core/src/Microsoft.Bot.Core/Activities/EventActivity.cs
new file mode 100644
index 00000000..c2d9154a
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/EventActivity.cs
@@ -0,0 +1,63 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an event activity.
+/// </summary>
+public class EventActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the name of the event. See <see cref="EventNames"/> for common values.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="EventActivity"/> class.
+    /// </summary>
+    public EventActivity() : base(ActivityTypes.Event)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="EventActivity"/> class with the specified event name.
+    /// </summary>
+    /// <param name="name">The event name.</param>
+    public EventActivity(string name) : base(ActivityTypes.Event)
+    {
+        Name = name;
+    }
+}
+
+/// <summary>
+/// String constants for event activity names.
+/// </summary>
+public static class EventNames
+{
+    /// <summary>
+    /// Read receipt event name.
+    /// </summary>
+    public const string ReadReceipt = "application/vnd.microsoft.readReceipt";
+
+    /// <summary>
+    /// Meeting start event name.
+    /// </summary>
+    public const string MeetingStart = "application/vnd.microsoft.meetingStart";
+
+    /// <summary>
+    /// Meeting end event name.
+    /// </summary>
+    public const string MeetingEnd = "application/vnd.microsoft.meetingEnd";
+
+    /// <summary>
+    /// Meeting participant join event name.
+    /// </summary>
+    public const string MeetingParticipantJoin = "application/vnd.microsoft.meetingParticipantJoin";
+
+    /// <summary>
+    /// Meeting participant leave event name.
+    /// </summary>
+    public const string MeetingParticipantLeave = "application/vnd.microsoft.meetingParticipantLeave";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/ExecuteActionActivity.cs b/core/src/Microsoft.Bot.Core/Activities/ExecuteActionActivity.cs
new file mode 100644
index 00000000..514f6c3b
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/ExecuteActionActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an execute action invoke activity.
+/// </summary>
+public class ExecuteActionActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ExecuteActionActivity"/> class.
+    /// </summary>
+    public ExecuteActionActivity() : base("actionableMessage/executeAction")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/FileConsentActivity.cs b/core/src/Microsoft.Bot.Core/Activities/FileConsentActivity.cs
new file mode 100644
index 00000000..004339e4
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/FileConsentActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a file consent invoke activity.
+/// </summary>
+public class FileConsentActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="FileConsentActivity"/> class.
+    /// </summary>
+    public FileConsentActivity() : base("fileConsent/invoke")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/HandoffActivity.cs b/core/src/Microsoft.Bot.Core/Activities/HandoffActivity.cs
new file mode 100644
index 00000000..4850892c
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/HandoffActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a handoff invoke activity.
+/// </summary>
+public class HandoffActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HandoffActivity"/> class.
+    /// </summary>
+    public HandoffActivity() : base("handoff/action")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/InstallUpdateActivity.cs b/core/src/Microsoft.Bot.Core/Activities/InstallUpdateActivity.cs
new file mode 100644
index 00000000..72b0de68
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/InstallUpdateActivity.cs
@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an installation update activity.
+/// </summary>
+public class InstallUpdateActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the action for the installation update. See <see cref="InstallUpdateActions"/> for common values.
+    /// </summary>
+    [JsonPropertyName("action")]
+    public string? Action { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InstallUpdateActivity"/> class.
+    /// </summary>
+    public InstallUpdateActivity() : base(ActivityTypes.InstallationUpdate)
+    {
+    }
+}
+
+/// <summary>
+/// String constants for installation update actions.
+/// </summary>
+public static class InstallUpdateActions
+{
+    /// <summary>
+    /// Add action.
+    /// </summary>
+    public const string Add = "add";
+
+    /// <summary>
+    /// Remove action.
+    /// </summary>
+    public const string Remove = "remove";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/InvokeActivity.cs b/core/src/Microsoft.Bot.Core/Activities/InvokeActivity.cs
new file mode 100644
index 00000000..dadfee15
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/InvokeActivity.cs
@@ -0,0 +1,161 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents an invoke activity.
+/// </summary>
+public class InvokeActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the name of the operation. See <see cref="InvokeNames"/> for common values.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string? Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value that is associated with the activity.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public object? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InvokeActivity"/> class.
+    /// </summary>
+    public InvokeActivity()
+    {
+        Type = ActivityTypes.Invoke;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InvokeActivity"/> class with the specified name.
+    /// </summary>
+    /// <param name="name">The invoke operation name.</param>
+    public InvokeActivity(string name)
+    {
+        Type = ActivityTypes.Invoke;
+        Name = name;
+    }
+}
+
+/// <summary>
+/// String constants for invoke activity names.
+/// </summary>
+public static class InvokeNames
+{
+    /// <summary>
+    /// Execute action invoke name.
+    /// </summary>
+    public const string ExecuteAction = "actionableMessage/executeAction";
+
+    /// <summary>
+    /// File consent invoke name.
+    /// </summary>
+    public const string FileConsent = "fileConsent/invoke";
+
+    /// <summary>
+    /// Handoff invoke name.
+    /// </summary>
+    public const string Handoff = "handoff/action";
+
+    /// <summary>
+    /// Search invoke name.
+    /// </summary>
+    public const string Search = "search";
+
+    /// <summary>
+    /// Adaptive card action invoke name.
+    /// </summary>
+    public const string AdaptiveCardAction = "adaptiveCard/action";
+
+    /// <summary>
+    /// Config fetch invoke name.
+    /// </summary>
+    public const string ConfigFetch = "config/fetch";
+
+    /// <summary>
+    /// Config submit invoke name.
+    /// </summary>
+    public const string ConfigSubmit = "config/submit";
+
+    /// <summary>
+    /// Tab fetch invoke name.
+    /// </summary>
+    public const string TabFetch = "tab/fetch";
+
+    /// <summary>
+    /// Tab submit invoke name.
+    /// </summary>
+    public const string TabSubmit = "tab/submit";
+
+    /// <summary>
+    /// Task fetch invoke name.
+    /// </summary>
+    public const string TaskFetch = "task/fetch";
+
+    /// <summary>
+    /// Task submit invoke name.
+    /// </summary>
+    public const string TaskSubmit = "task/submit";
+
+    /// <summary>
+    /// Sign-in token exchange invoke name.
+    /// </summary>
+    public const string SignInTokenExchange = "signin/tokenExchange";
+
+    /// <summary>
+    /// Sign-in verify state invoke name.
+    /// </summary>
+    public const string SignInVerifyState = "signin/verifyState";
+
+    /// <summary>
+    /// Message submit action invoke name.
+    /// </summary>
+    public const string MessageSubmitAction = "message/submitAction";
+
+    /// <summary>
+    /// Message extension anonymous query link invoke name.
+    /// </summary>
+    public const string MessageExtensionAnonQueryLink = "composeExtension/anonymousQueryLink";
+
+    /// <summary>
+    /// Message extension card button clicked invoke name.
+    /// </summary>
+    public const string MessageExtensionCardButtonClicked = "composeExtension/onCardButtonClicked";
+
+    /// <summary>
+    /// Message extension fetch task invoke name.
+    /// </summary>
+    public const string MessageExtensionFetchTask = "composeExtension/fetchTask";
+
+    /// <summary>
+    /// Message extension query invoke name.
+    /// </summary>
+    public const string MessageExtensionQuery = "composeExtension/query";
+
+    /// <summary>
+    /// Message extension query link invoke name.
+    /// </summary>
+    public const string MessageExtensionQueryLink = "composeExtension/queryLink";
+
+    /// <summary>
+    /// Message extension query setting URL invoke name.
+    /// </summary>
+    public const string MessageExtensionQuerySettingUrl = "composeExtension/querySettingUrl";
+
+    /// <summary>
+    /// Message extension select item invoke name.
+    /// </summary>
+    public const string MessageExtensionSelectItem = "composeExtension/selectItem";
+
+    /// <summary>
+    /// Message extension setting invoke name.
+    /// </summary>
+    public const string MessageExtensionSetting = "composeExtension/setting";
+
+    /// <summary>
+    /// Message extension submit action invoke name.
+    /// </summary>
+    public const string MessageExtensionSubmitAction = "composeExtension/submitAction";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MeetingEndActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MeetingEndActivity.cs
new file mode 100644
index 00000000..1d9b735d
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MeetingEndActivity.cs
@@ -0,0 +1,62 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a meeting end event activity.
+/// </summary>
+public class MeetingEndActivity : EventActivity
+{
+    /// <summary>
+    /// Gets or sets a value that is associated with the activity.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public MeetingEndActivityValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MeetingEndActivity"/> class.
+    /// </summary>
+    public MeetingEndActivity() : base(EventNames.MeetingEnd)
+    {
+    }
+}
+
+/// <summary>
+/// A value that is associated with a meeting end activity.
+/// </summary>
+#pragma warning disable CA1056 // URI properties should not be strings
+public class MeetingEndActivityValue
+#pragma warning restore CA1056 // URI properties should not be strings
+{
+    /// <summary>
+    /// Gets or sets the meeting's ID, encoded as a BASE64 string.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the meeting's type.
+    /// </summary>
+    [JsonPropertyName("meetingType")]
+    public string? MeetingType { get; set; }
+
+    /// <summary>
+    /// Gets or sets the URL used to join the meeting.
+    /// </summary>
+    [JsonPropertyName("joinUrl")]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1056:URI properties should not be strings", Justification = "Meeting activity schema uses string for JoinUrl")]
+    public string? JoinUrl { get; set; }
+
+    /// <summary>
+    /// Gets or sets the title of the meeting.
+    /// </summary>
+    [JsonPropertyName("title")]
+    public string? Title { get; set; }
+
+    /// <summary>
+    /// Gets or sets the timestamp for meeting end, in UTC.
+    /// </summary>
+    [JsonPropertyName("endTime")]
+    public DateTime? EndTime { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantJoinActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantJoinActivity.cs
new file mode 100644
index 00000000..a6f858eb
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantJoinActivity.cs
@@ -0,0 +1,73 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a meeting participant join event activity.
+/// </summary>
+public class MeetingParticipantJoinActivity : EventActivity
+{
+    /// <summary>
+    /// Gets or sets a value that is associated with the activity.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public MeetingParticipantJoinActivityValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MeetingParticipantJoinActivity"/> class.
+    /// </summary>
+    public MeetingParticipantJoinActivity() : base(EventNames.MeetingParticipantJoin)
+    {
+    }
+}
+
+/// <summary>
+/// A value that is associated with a meeting participant join activity.
+/// </summary>
+public class MeetingParticipantJoinActivityValue
+{
+    /// <summary>
+    /// Gets or sets the participants info.
+    /// </summary>
+    [JsonPropertyName("members")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<MeetingParticipantMember>? Members { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
+
+/// <summary>
+/// Represents a meeting participant member.
+/// </summary>
+public class MeetingParticipantMember
+{
+    /// <summary>
+    /// Gets or sets the participant account.
+    /// </summary>
+    [JsonPropertyName("user")]
+    public Account? User { get; set; }
+
+    /// <summary>
+    /// Gets or sets the participant's meeting info.
+    /// </summary>
+    [JsonPropertyName("meeting")]
+    public MeetingParticipantMeetingInfo? Meeting { get; set; }
+}
+
+/// <summary>
+/// Represents meeting participant meeting information.
+/// </summary>
+public class MeetingParticipantMeetingInfo
+{
+    /// <summary>
+    /// Gets or sets a value indicating whether the user is in the meeting.
+    /// </summary>
+    [JsonPropertyName("inMeeting")]
+    public bool InMeeting { get; set; }
+
+    /// <summary>
+    /// Gets or sets the participant's role in the meeting. See <see cref="Roles"/> for common values.
+    /// </summary>
+    [JsonPropertyName("role")]
+    public string? Role { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantLeaveActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantLeaveActivity.cs
new file mode 100644
index 00000000..7403857e
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MeetingParticipantLeaveActivity.cs
@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a meeting participant leave event activity.
+/// </summary>
+public class MeetingParticipantLeaveActivity : EventActivity
+{
+    /// <summary>
+    /// Gets or sets a value that is associated with the activity.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public MeetingParticipantLeaveActivityValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MeetingParticipantLeaveActivity"/> class.
+    /// </summary>
+    public MeetingParticipantLeaveActivity() : base(EventNames.MeetingParticipantLeave)
+    {
+    }
+}
+
+/// <summary>
+/// A value that is associated with a meeting participant leave activity.
+/// </summary>
+public class MeetingParticipantLeaveActivityValue
+{
+    /// <summary>
+    /// Gets or sets the participants info.
+    /// </summary>
+    [JsonPropertyName("members")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<MeetingParticipantMember>? Members { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MeetingStartActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MeetingStartActivity.cs
new file mode 100644
index 00000000..10724509
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MeetingStartActivity.cs
@@ -0,0 +1,62 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a meeting start event activity.
+/// </summary>
+public class MeetingStartActivity : EventActivity
+{
+    /// <summary>
+    /// Gets or sets a value that is associated with the activity.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public MeetingStartActivityValue? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MeetingStartActivity"/> class.
+    /// </summary>
+    public MeetingStartActivity() : base(EventNames.MeetingStart)
+    {
+    }
+}
+
+/// <summary>
+/// A value that is associated with a meeting start activity.
+/// </summary>
+#pragma warning disable CA1056 // URI properties should not be strings
+public class MeetingStartActivityValue
+#pragma warning restore CA1056 // URI properties should not be strings
+{
+    /// <summary>
+    /// Gets or sets the meeting's ID, encoded as a BASE64 string.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the meeting's type.
+    /// </summary>
+    [JsonPropertyName("meetingType")]
+    public string? MeetingType { get; set; }
+
+    /// <summary>
+    /// Gets or sets the URL used to join the meeting.
+    /// </summary>
+    [JsonPropertyName("joinUrl")]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1056:URI properties should not be strings", Justification = "Meeting activity schema uses string for JoinUrl")]
+    public string? JoinUrl { get; set; }
+
+    /// <summary>
+    /// Gets or sets the title of the meeting.
+    /// </summary>
+    [JsonPropertyName("title")]
+    public string? Title { get; set; }
+
+    /// <summary>
+    /// Gets or sets the timestamp for meeting start, in UTC.
+    /// </summary>
+    [JsonPropertyName("startTime")]
+    public DateTime? StartTime { get; set; }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageActivity.cs
new file mode 100644
index 00000000..12d4fcc5
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageActivity.cs
@@ -0,0 +1,180 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message activity.
+/// </summary>
+public class MessageActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the text content of the message.
+    /// </summary>
+    [JsonPropertyName("text")]
+    public string? Text { get; set; }
+
+    /// <summary>
+    /// Gets or sets the SSML speak content of the message.
+    /// </summary>
+    [JsonPropertyName("speak")]
+    public string? Speak { get; set; }
+
+    /// <summary>
+    /// Gets or sets the input hint. See <see cref="InputHints"/> for common values.
+    /// </summary>
+    [JsonPropertyName("inputHint")]
+    public string? InputHint { get; set; }
+
+    /// <summary>
+    /// Gets or sets the summary of the message.
+    /// </summary>
+    [JsonPropertyName("summary")]
+    public string? Summary { get; set; }
+
+    /// <summary>
+    /// Gets or sets the text format. See <see cref="TextFormats"/> for common values.
+    /// </summary>
+    [JsonPropertyName("textFormat")]
+    public string? TextFormat { get; set; }
+
+    /// <summary>
+    /// Gets or sets the attachment layout.
+    /// </summary>
+    [JsonPropertyName("attachmentLayout")]
+    public string? AttachmentLayout { get; set; }
+
+    /// <summary>
+    /// Gets or sets the importance. See <see cref="ImportanceLevels"/> for common values.
+    /// </summary>
+    [JsonPropertyName("importance")]
+    public string? Importance { get; set; }
+
+    /// <summary>
+    /// Gets or sets the delivery mode. See <see cref="DeliveryModes"/> for common values.
+    /// </summary>
+    [JsonPropertyName("deliveryMode")]
+    public string? DeliveryMode { get; set; }
+
+    /// <summary>
+    /// Gets or sets the expiration time of the message.
+    /// </summary>
+    [JsonPropertyName("expiration")]
+    public DateTime? Expiration { get; set; }
+
+    /// <summary>
+    /// Gets or sets the value associated with the message.
+    /// </summary>
+    [JsonPropertyName("value")]
+    public object? Value { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageActivity"/> class.
+    /// </summary>
+    public MessageActivity() : base(ActivityTypes.Message)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageActivity"/> class with the specified text.
+    /// </summary>
+    /// <param name="text">The text content of the message.</param>
+    public MessageActivity(string text) : base(ActivityTypes.Message)
+    {
+        Text = text;
+    }
+}
+
+/// <summary>
+/// String constants for input hints.
+/// </summary>
+public static class InputHints
+{
+    /// <summary>
+    /// Accepting input hint.
+    /// </summary>
+    public const string AcceptingInput = "acceptingInput";
+
+    /// <summary>
+    /// Ignoring input hint.
+    /// </summary>
+    public const string IgnoringInput = "ignoringInput";
+
+    /// <summary>
+    /// Expecting input hint.
+    /// </summary>
+    public const string ExpectingInput = "expectingInput";
+}
+
+/// <summary>
+/// String constants for text formats.
+/// </summary>
+public static class TextFormats
+{
+    /// <summary>
+    /// Plain text format.
+    /// </summary>
+    public const string Plain = "plain";
+
+    /// <summary>
+    /// Markdown text format.
+    /// </summary>
+    public const string Markdown = "markdown";
+
+    /// <summary>
+    /// XML text format.
+    /// </summary>
+    public const string Xml = "xml";
+}
+
+/// <summary>
+/// String constants for importance levels.
+/// </summary>
+public static class ImportanceLevels
+{
+    /// <summary>
+    /// Low importance.
+    /// </summary>
+    public const string Low = "low";
+
+    /// <summary>
+    /// Normal importance.
+    /// </summary>
+    public const string Normal = "normal";
+
+    /// <summary>
+    /// High importance.
+    /// </summary>
+    public const string High = "high";
+
+    /// <summary>
+    /// Urgent importance.
+    /// </summary>
+    public const string Urgent = "urgent";
+}
+
+/// <summary>
+/// String constants for delivery modes.
+/// </summary>
+public static class DeliveryModes
+{
+    /// <summary>
+    /// Normal delivery mode.
+    /// </summary>
+    public const string Normal = "normal";
+
+    /// <summary>
+    /// Notification delivery mode.
+    /// </summary>
+    public const string Notification = "notification";
+
+    /// <summary>
+    /// Ephemeral delivery mode.
+    /// </summary>
+    public const string Ephemeral = "ephemeral";
+
+    /// <summary>
+    /// Expected replies delivery mode.
+    /// </summary>
+    public const string ExpectedReplies = "expectReplies";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageDeleteActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageDeleteActivity.cs
new file mode 100644
index 00000000..6aa4a88e
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageDeleteActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message delete activity.
+/// </summary>
+public class MessageDeleteActivity : Activity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageDeleteActivity"/> class.
+    /// </summary>
+    public MessageDeleteActivity() : base(ActivityTypes.MessageDelete)
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageExtensionActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageExtensionActivity.cs
new file mode 100644
index 00000000..115340ef
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageExtensionActivity.cs
@@ -0,0 +1,121 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message extension anonymous query link invoke activity.
+/// </summary>
+public class MessageExtensionAnonQueryLinkActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionAnonQueryLinkActivity"/> class.
+    /// </summary>
+    public MessageExtensionAnonQueryLinkActivity() : base("composeExtension/anonymousQueryLink")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension card button clicked invoke activity.
+/// </summary>
+public class MessageExtensionCardButtonClickedActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionCardButtonClickedActivity"/> class.
+    /// </summary>
+    public MessageExtensionCardButtonClickedActivity() : base("composeExtension/onCardButtonClicked")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension fetch task invoke activity.
+/// </summary>
+public class MessageExtensionFetchTaskActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionFetchTaskActivity"/> class.
+    /// </summary>
+    public MessageExtensionFetchTaskActivity() : base("composeExtension/fetchTask")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension query invoke activity.
+/// </summary>
+public class MessageExtensionQueryActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionQueryActivity"/> class.
+    /// </summary>
+    public MessageExtensionQueryActivity() : base("composeExtension/query")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension query link invoke activity.
+/// </summary>
+public class MessageExtensionQueryLinkActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionQueryLinkActivity"/> class.
+    /// </summary>
+    public MessageExtensionQueryLinkActivity() : base("composeExtension/queryLink")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension query setting URL invoke activity.
+/// </summary>
+public class MessageExtensionQuerySettingUrlActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionQuerySettingUrlActivity"/> class.
+    /// </summary>
+    public MessageExtensionQuerySettingUrlActivity() : base("composeExtension/querySettingUrl")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension select item invoke activity.
+/// </summary>
+public class MessageExtensionSelectItemActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionSelectItemActivity"/> class.
+    /// </summary>
+    public MessageExtensionSelectItemActivity() : base("composeExtension/selectItem")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension setting invoke activity.
+/// </summary>
+public class MessageExtensionSettingActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionSettingActivity"/> class.
+    /// </summary>
+    public MessageExtensionSettingActivity() : base("composeExtension/setting")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message extension submit action invoke activity.
+/// </summary>
+public class MessageExtensionSubmitActionActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageExtensionSubmitActionActivity"/> class.
+    /// </summary>
+    public MessageExtensionSubmitActionActivity() : base("composeExtension/submitAction")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageInvokeActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageInvokeActivity.cs
new file mode 100644
index 00000000..7339b9a7
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageInvokeActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message submit action invoke activity.
+/// </summary>
+public class MessageSubmitActionActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageSubmitActionActivity"/> class.
+    /// </summary>
+    public MessageSubmitActionActivity() : base("message/submitAction")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageReactionActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageReactionActivity.cs
new file mode 100644
index 00000000..937b38eb
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageReactionActivity.cs
@@ -0,0 +1,148 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message reaction activity.
+/// </summary>
+public class MessageReactionActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the collection of reactions added.
+    /// </summary>
+    [JsonPropertyName("reactionsAdded")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<MessageReaction>? ReactionsAdded { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+
+    /// <summary>
+    /// Gets or sets the collection of reactions removed.
+    /// </summary>
+    [JsonPropertyName("reactionsRemoved")]
+#pragma warning disable CA2227 // Collection properties should be read only
+    public IList<MessageReaction>? ReactionsRemoved { get; set; }
+#pragma warning restore CA2227 // Collection properties should be read only
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageReactionActivity"/> class.
+    /// </summary>
+    public MessageReactionActivity() : base(ActivityTypes.MessageReaction)
+    {
+    }
+}
+
+/// <summary>
+/// Represents a message reaction.
+/// </summary>
+public class MessageReaction
+{
+    /// <summary>
+    /// Gets or sets the type of reaction. See <see cref="ReactionTypes"/> for common values.
+    /// </summary>
+    [JsonPropertyName("type")]
+    public string? Type { get; set; }
+
+    /// <summary>
+    /// Gets or sets the timestamp of when the user reacted to the message.
+    /// </summary>
+    [JsonPropertyName("createdDateTime")]
+    public string? CreatedDateTime { get; set; }
+
+    /// <summary>
+    /// Gets or sets the user with which the reaction is associated.
+    /// </summary>
+    [JsonPropertyName("user")]
+    public ReactionUser? User { get; set; }
+}
+
+/// <summary>
+/// Represents a user associated with a reaction.
+/// </summary>
+public class ReactionUser
+{
+    /// <summary>
+    /// Gets or sets the ID of the user.
+    /// </summary>
+    [JsonPropertyName("id")]
+    public string? Id { get; set; }
+
+    /// <summary>
+    /// Gets or sets the identity type of the user. See <see cref="UserIdentityTypes"/> for common values.
+    /// </summary>
+    [JsonPropertyName("userIdentityType")]
+    public string? UserIdentityType { get; set; }
+
+    /// <summary>
+    /// Gets or sets the plaintext display name of the user.
+    /// </summary>
+    [JsonPropertyName("displayName")]
+    public string? DisplayName { get; set; }
+}
+
+/// <summary>
+/// String constants for reaction types.
+/// </summary>
+public static class ReactionTypes
+{
+    /// <summary>
+    /// Like reaction.
+    /// </summary>
+    public const string Like = "like";
+
+    /// <summary>
+    /// Heart reaction.
+    /// </summary>
+    public const string Heart = "heart";
+
+    /// <summary>
+    /// Laugh reaction.
+    /// </summary>
+    public const string Laugh = "laugh";
+
+    /// <summary>
+    /// Surprise reaction.
+    /// </summary>
+    public const string Surprise = "surprise";
+
+    /// <summary>
+    /// Sad reaction.
+    /// </summary>
+    public const string Sad = "sad";
+
+    /// <summary>
+    /// Angry reaction.
+    /// </summary>
+    public const string Angry = "angry";
+
+    /// <summary>
+    /// Plus one reaction.
+    /// </summary>
+    public const string PlusOne = "plusOne";
+}
+
+/// <summary>
+/// String constants for user identity types.
+/// </summary>
+public static class UserIdentityTypes
+{
+    /// <summary>
+    /// Azure AD user.
+    /// </summary>
+    public const string AadUser = "aadUser";
+
+    /// <summary>
+    /// On-premise Azure AD user.
+    /// </summary>
+    public const string OnPremiseAadUser = "onPremiseAadUser";
+
+    /// <summary>
+    /// Anonymous guest user.
+    /// </summary>
+    public const string AnonymousGuest = "anonymousGuest";
+
+    /// <summary>
+    /// Federated user.
+    /// </summary>
+    public const string FederatedUser = "federatedUser";
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/MessageUpdateActivity.cs b/core/src/Microsoft.Bot.Core/Activities/MessageUpdateActivity.cs
new file mode 100644
index 00000000..077bcec7
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/MessageUpdateActivity.cs
@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a message update activity.
+/// </summary>
+public class MessageUpdateActivity : MessageActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageUpdateActivity"/> class.
+    /// </summary>
+    public MessageUpdateActivity() : base()
+    {
+        Type = ActivityTypes.MessageUpdate;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MessageUpdateActivity"/> class with the specified text.
+    /// </summary>
+    /// <param name="text">The text content of the message.</param>
+    public MessageUpdateActivity(string text) : base(text)
+    {
+        Type = ActivityTypes.MessageUpdate;
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/ReadReceiptActivity.cs b/core/src/Microsoft.Bot.Core/Activities/ReadReceiptActivity.cs
new file mode 100644
index 00000000..c25d6076
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/ReadReceiptActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a read receipt event activity.
+/// </summary>
+public class ReadReceiptActivity : EventActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ReadReceiptActivity"/> class.
+    /// </summary>
+    public ReadReceiptActivity() : base(EventNames.ReadReceipt)
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/SearchActivity.cs b/core/src/Microsoft.Bot.Core/Activities/SearchActivity.cs
new file mode 100644
index 00000000..823502bd
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/SearchActivity.cs
@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a search invoke activity.
+/// </summary>
+public class SearchActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SearchActivity"/> class.
+    /// </summary>
+    public SearchActivity() : base("search")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/SignInActivity.cs b/core/src/Microsoft.Bot.Core/Activities/SignInActivity.cs
new file mode 100644
index 00000000..2a08e830
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/SignInActivity.cs
@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a sign-in token exchange invoke activity.
+/// </summary>
+public class SignInTokenExchangeActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SignInTokenExchangeActivity"/> class.
+    /// </summary>
+    public SignInTokenExchangeActivity() : base("signin/tokenExchange")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a sign-in verify state invoke activity.
+/// </summary>
+public class SignInVerifyStateActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SignInVerifyStateActivity"/> class.
+    /// </summary>
+    public SignInVerifyStateActivity() : base("signin/verifyState")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/TabActivity.cs b/core/src/Microsoft.Bot.Core/Activities/TabActivity.cs
new file mode 100644
index 00000000..9f526f92
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/TabActivity.cs
@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a tab fetch invoke activity.
+/// </summary>
+public class TabFetchActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TabFetchActivity"/> class.
+    /// </summary>
+    public TabFetchActivity() : base("tab/fetch")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a tab submit invoke activity.
+/// </summary>
+public class TabSubmitActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TabSubmitActivity"/> class.
+    /// </summary>
+    public TabSubmitActivity() : base("tab/submit")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/TaskActivity.cs b/core/src/Microsoft.Bot.Core/Activities/TaskActivity.cs
new file mode 100644
index 00000000..4273e488
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/TaskActivity.cs
@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a task fetch invoke activity.
+/// </summary>
+public class TaskFetchActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TaskFetchActivity"/> class.
+    /// </summary>
+    public TaskFetchActivity() : base("task/fetch")
+    {
+    }
+}
+
+/// <summary>
+/// Represents a task submit invoke activity.
+/// </summary>
+public class TaskSubmitActivity : InvokeActivity
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TaskSubmitActivity"/> class.
+    /// </summary>
+    public TaskSubmitActivity() : base("task/submit")
+    {
+    }
+}
diff --git a/core/src/Microsoft.Bot.Core/Activities/TypingActivity.cs b/core/src/Microsoft.Bot.Core/Activities/TypingActivity.cs
new file mode 100644
index 00000000..c243a166
--- /dev/null
+++ b/core/src/Microsoft.Bot.Core/Activities/TypingActivity.cs
@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Microsoft.Bot.Core.Activities;
+
+/// <summary>
+/// Represents a typing activity.
+/// </summary>
+public class TypingActivity : Activity
+{
+    /// <summary>
+    /// Gets or sets the text content of the typing activity.
+    /// </summary>
+    [JsonPropertyName("text")]
+    public string? Text { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TypingActivity"/> class.
+    /// </summary>
+    public TypingActivity() : base(ActivityTypes.Typing)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TypingActivity"/> class with the specified text.
+    /// </summary>
+    /// <param name="text">The text content.</param>
+    public TypingActivity(string text) : base(ActivityTypes.Typing)
+    {
+        Text = text;
+    }
+}