diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92c397a..cdeee2c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,14 @@ All notable changes to this project will be documented in this file. This change
 
 ## [Unreleased]
 
+### Added (upstream PR #605 sync)
+- `:copilot/subagent.deselected` event type added to `::event-type` spec, `event-types` var, and API reference table (upstream PR #605 / CLI 0.0.420).
+- `:github-reference` attachment type: represents a GitHub issue, PR, or discussion attached to a user message. Added to `::attachment-type` spec and `::attachment` spec. Data fields: `number`, `title`, `reference-type` (`"issue"/"pr"/"discussion"`), `state`, `url` (upstream PR #605).
+- `::assistant.turn_start-data` spec with `turn-id` (required) and `interaction-id` (optional).
+- `:interaction-id` optional field added to `::user.message-data`, `::assistant.turn_start-data`, `::assistant.message_delta-data`, and `::tool.execution_complete-data` specs (upstream PR #605).
+- `:model` optional field added to `::tool.execution_complete-data` spec — model used for the tool execution (upstream PR #605).
+- `:plugin-name` and `:plugin-version` optional fields added to `::skill.invoked-data` spec (upstream PR #605).
+
 ### Added (documentation)
 - Azure Managed Identity BYOK guide (`doc/auth/azure-managed-identity.md`): shows how to use `DefaultAzureCredential` with short-lived bearer tokens for Azure AI Foundry, with Clojure examples for basic usage and token refresh (upstream PR #498).
 - Updated BYOK limitations to link to the Managed Identity workaround instead of listing it as fully unsupported.
diff --git a/doc/reference/API.md b/doc/reference/API.md
index 92dc366..ea09fee 100644
--- a/doc/reference/API.md
+++ b/doc/reference/API.md
@@ -594,6 +594,7 @@ Send a message to the session. Returns immediately with the message ID.
 | `:file` | `:type`, `:path` | `:display-name`, `:line-range` | File attachment |
 | `:directory` | `:type`, `:path` | `:display-name`, `:line-range` | Directory attachment |
 | `:selection` | `:type`, `:file-path`, `:display-name` | `:selection-range`, `:text` | Code selection attachment |
+| `:github-reference` | `:type`, `:number`, `:title`, `:reference-type`, `:state`, `:url` | — | GitHub issue, PR, or discussion reference |
 
 `:line-range` is a map with `:start` and `:end` line numbers (zero-based) to restrict the attachment to a range of lines:
 
@@ -887,6 +888,7 @@ copilot/tool-events
 | `:copilot/subagent.completed` | Subagent completed |
 | `:copilot/subagent.failed` | Subagent failed |
 | `:copilot/subagent.selected` | Subagent selected |
+| `:copilot/subagent.deselected` | Subagent deselected |
 | `:copilot/hook.start` | Hook invocation started |
 | `:copilot/hook.end` | Hook invocation finished |
 | `:copilot/system.message` | System message emitted |
diff --git a/src/github/copilot_sdk.clj b/src/github/copilot_sdk.clj
index 969bf68..b65ae79 100644
--- a/src/github/copilot_sdk.clj
+++ b/src/github/copilot_sdk.clj
@@ -72,6 +72,7 @@
     :copilot/subagent.completed
     :copilot/subagent.failed
     :copilot/subagent.selected
+    :copilot/subagent.deselected
     :copilot/skill.invoked
     :copilot/hook.start
     :copilot/hook.end
diff --git a/src/github/copilot_sdk/specs.clj b/src/github/copilot_sdk/specs.clj
index 6a95fd8..4c25333 100644
--- a/src/github/copilot_sdk/specs.clj
+++ b/src/github/copilot_sdk/specs.clj
@@ -240,7 +240,7 @@
 ;; -----------------------------------------------------------------------------
 
 (s/def ::prompt ::non-blank-string)
-(s/def ::attachment-type #{:file :directory :selection})
+(s/def ::attachment-type #{:file :directory :selection :github-reference})
 (s/def ::type ::attachment-type)
 (s/def ::path ::non-blank-string)
 (s/def ::file-path ::non-blank-string)
@@ -274,9 +274,26 @@
                  :opt-un [::selection-range ::text])
          #(= :selection (:type %))))
 
+;; GitHub reference attachment (issue, PR, or discussion)
+;; Note: ::state is already defined as (instance? Atom) for the client record,
+;; so we cannot use s/keys here — manual predicates validate the :state field instead.
+(s/def ::number nat-int?)
+(s/def ::reference-type #{"issue" "pr" "discussion"})
+(s/def ::url string?)
+(s/def ::attachment-state string?)
+(s/def ::github-reference-attachment
+  (s/and map?
+         #(= :github-reference (:type %))
+         #(nat-int? (:number %))
+         #(string? (:title %))
+         #(contains? #{"issue" "pr" "discussion"} (:reference-type %))
+         #(string? (:state %))
+         #(string? (:url %))))
+
 (s/def ::attachment
   (s/or :file-or-directory ::file-or-directory-attachment
-        :selection ::selection-attachment))
+        :selection ::selection-attachment
+        :github-reference ::github-reference-attachment))
 
 (s/def ::attachments (s/coll-of ::attachment))
 (s/def ::mode #{:enqueue :immediate})
@@ -365,6 +382,7 @@
     :copilot/tool.user_requested :copilot/tool.execution_start :copilot/tool.execution_partial_result
     :copilot/tool.execution_progress :copilot/tool.execution_complete
     :copilot/subagent.started :copilot/subagent.completed :copilot/subagent.failed :copilot/subagent.selected
+    :copilot/subagent.deselected
     :copilot/skill.invoked
     :copilot/hook.start :copilot/hook.end
     :copilot/system.message})
@@ -381,20 +399,26 @@
 (s/def ::session.idle-data map?)
 
 (s/def ::agent-mode #{:interactive :plan :autopilot :shell})
+(s/def ::interaction-id string?)
 
 (s/def ::user.message-data
   (s/keys :req-un [::content]
-          :opt-un [::transformed-content ::attachments ::source ::agent-mode]))
+          :opt-un [::transformed-content ::attachments ::source ::agent-mode ::interaction-id]))
 
 (s/def ::assistant.message-data
   (s/keys :req-un [::message-id ::content]
           :opt-un [::tool-requests ::parent-tool-call-id]))
 
 (s/def ::total-response-size-bytes nat-int?)
+(s/def ::turn-id ::non-blank-string)
+
+(s/def ::assistant.turn_start-data
+  (s/keys :req-un [::turn-id]
+          :opt-un [::interaction-id]))
 
 (s/def ::assistant.message_delta-data
   (s/keys :req-un [::message-id ::delta-content]
-          :opt-un [::parent-tool-call-id]))
+          :opt-un [::parent-tool-call-id ::interaction-id]))
 
 (s/def ::assistant.streaming_delta-data
   (s/keys :req-un [::total-response-size-bytes]))
@@ -410,7 +434,8 @@
 
 (s/def ::tool.execution_complete-data
   (s/keys :req-un [::tool-call-id ::success?]
-          :opt-un [::is-user-requested? ::result ::error ::tool-telemetry ::parent-tool-call-id]))
+          :opt-un [::is-user-requested? ::result ::error ::tool-telemetry ::parent-tool-call-id
+                   ::model ::interaction-id]))
 
 ;; Session shutdown event
 (s/def ::shutdown-type #{"routine" "error"})
@@ -465,10 +490,12 @@
 
 ;; Skill invoked event
 (s/def ::allowed-tools (s/coll-of string?))
+(s/def ::plugin-name string?)
+(s/def ::plugin-version string?)
 
 (s/def ::skill.invoked-data
   (s/keys :req-un [::name ::path ::content]
-          :opt-un [::allowed-tools]))
+          :opt-un [::allowed-tools ::plugin-name ::plugin-version]))
 
 ;; Generic session event
 (s/def ::session-event
@@ -641,4 +668,5 @@
 ;; Session model operations (session.model.getCurrent / switchTo)
 ;; -----------------------------------------------------------------------------
 
+(s/def ::model string?)
 (s/def ::model-id (s/nilable string?))
diff --git a/src/github/copilot_sdk/util.clj b/src/github/copilot_sdk/util.clj
index 7be98fe..147f773 100644
--- a/src/github/copilot_sdk/util.clj
+++ b/src/github/copilot_sdk/util.clj
@@ -97,6 +97,14 @@
       (:selection-range att) (assoc :selection (clj->wire (:selection-range att)))
       (:text att) (assoc :text (:text att)))
 
+    :github-reference
+    {:type "github_reference"
+     :number (:number att)
+     :title (:title att)
+     :referenceType (name (:reference-type att))
+     :state (:state att)
+     :url (:url att)}
+
     ;; :file and :directory
     (cond-> {:type (name (:type att))
              :path (:path att)}