feat(api): add phase field to Message in conversations

Author: stainless-app[bot]

.stats.yml

@@ -1,4 +1,4 @@
 configured_endpoints: 151
-openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/openai%2Fopenai-2fab88288cbbe872f5d61d1d47da2286662a123b4312bc7fc36addba6607cd67.yml
-openapi_spec_hash: a7ee80374e409ed9ecc8ea2e3cd31071
+openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/openai%2Fopenai-89e54b8e2c185d30e869f73e7798308d56a6a835a675d54628dd86836f147879.yml
+openapi_spec_hash: 85b0dd465aa1a034f2764b0758671f21
 config_hash: 5635033cdc8c930255f8b529a78de722

src/resources/conversations/conversations.ts

@@ -170,6 +170,14 @@ export interface Message {
    * The type of the message. Always set to `message`.
    */
   type: 'message';
+
+  /**
+   * Labels an `assistant` message as intermediate commentary (`commentary`) or the
+   * final answer (`final_answer`). For models like `gpt-5.3-codex` and beyond, when
+   * sending follow-up requests, preserve and resend phase on all assistant messages
+   * — dropping it can degrade performance. Not used for user messages.
+   */
+  phase?: 'commentary' | 'final_answer' | null;
 }
 
 export namespace Message {