Default realtime startup to v2 model

Set the realtime config and Op::RealtimeConversationStart path to use v2 with gpt-realtime-1.5 by default. Add integration coverage for the outbound startup shape and keep legacy v1 tests explicit.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/config/src/config_toml.rs

@@ -457,7 +457,7 @@ pub enum RealtimeTransport {
 pub use codex_protocol::protocol::RealtimeConversationVersion as RealtimeWsVersion;
 pub use codex_protocol::protocol::RealtimeVoice;
 
-#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema)]
 #[schemars(deny_unknown_fields)]
 pub struct RealtimeConfig {
     pub version: RealtimeWsVersion,
@@ -467,6 +467,17 @@ pub struct RealtimeConfig {
     pub voice: Option<RealtimeVoice>,
 }
 
+impl Default for RealtimeConfig {
+    fn default() -> Self {
+        Self {
+            version: RealtimeWsVersion::V2,
+            session_type: RealtimeWsMode::default(),
+            transport: RealtimeTransport::default(),
+            voice: None,
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
 #[schemars(deny_unknown_fields)]
 pub struct RealtimeToml {

codex-rs/core/src/config/config_tests.rs

@@ -6482,6 +6482,35 @@ experimental_realtime_ws_model = "realtime-test-model"
     Ok(())
 }
 
+#[test]
+fn realtime_config_partial_table_uses_realtime_defaults() -> std::io::Result<()> {
+    let cfg: ConfigToml = toml::from_str(
+        r#"
+[realtime]
+voice = "marin"
+"#,
+    )
+    .expect("TOML deserialization should succeed");
+
+    let codex_home = TempDir::new()?;
+    let config = Config::load_from_base_config_with_overrides(
+        cfg,
+        ConfigOverrides::default(),
+        codex_home.path().to_path_buf(),
+    )?;
+
+    assert_eq!(
+        config.realtime,
+        RealtimeConfig {
+            version: RealtimeWsVersion::V2,
+            session_type: RealtimeWsMode::Conversational,
+            transport: RealtimeTransport::Websocket,
+            voice: Some(RealtimeVoice::Marin),
+        }
+    );
+    Ok(())
+}
+
 #[test]
 fn realtime_loads_from_config_toml() -> std::io::Result<()> {
     let cfg: ConfigToml = toml::from_str(

codex-rs/core/src/config/mod.rs

@@ -2094,11 +2094,14 @@ impl Config {
             experimental_realtime_ws_model: cfg.experimental_realtime_ws_model,
             realtime: cfg
                 .realtime
-                .map_or_else(RealtimeConfig::default, |realtime| RealtimeConfig {
-                    version: realtime.version.unwrap_or_default(),
-                    session_type: realtime.session_type.unwrap_or_default(),
-                    transport: realtime.transport.unwrap_or_default(),
-                    voice: realtime.voice,
+                .map_or_else(RealtimeConfig::default, |realtime| {
+                    let defaults = RealtimeConfig::default();
+                    RealtimeConfig {
+                        version: realtime.version.unwrap_or(defaults.version),
+                        session_type: realtime.session_type.unwrap_or(defaults.session_type),
+                        transport: realtime.transport.unwrap_or(defaults.transport),
+                        voice: realtime.voice,
+                    }
                 }),
             experimental_realtime_ws_backend_prompt: cfg.experimental_realtime_ws_backend_prompt,
             experimental_realtime_ws_startup_context: cfg.experimental_realtime_ws_startup_context,

codex-rs/core/src/realtime_conversation.rs

@@ -61,6 +61,7 @@ const USER_TEXT_IN_QUEUE_CAPACITY: usize = 64;
 const HANDOFF_OUT_QUEUE_CAPACITY: usize = 64;
 const OUTPUT_EVENTS_QUEUE_CAPACITY: usize = 256;
 const REALTIME_STARTUP_CONTEXT_TOKEN_BUDGET: usize = 5_000;
+const DEFAULT_REALTIME_MODEL: &str = "gpt-realtime-1.5";
 const ACTIVE_RESPONSE_CONFLICT_ERROR_PREFIX: &str =
     "Conversation already has an active response in progress:";
 
@@ -572,7 +573,12 @@ pub(crate) async fn build_realtime_session_config(
         (false, true) => prompt,
         (false, false) => format!("{prompt}\n\n{startup_context}"),
     };
-    let model = config.experimental_realtime_ws_model.clone();
+    let model = Some(
+        config
+            .experimental_realtime_ws_model
+            .clone()
+            .unwrap_or_else(|| DEFAULT_REALTIME_MODEL.to_string()),
+    );
     let event_parser = match config.realtime.version {
         RealtimeWsVersion::V1 => RealtimeEventParser::V1,
         RealtimeWsVersion::V2 => RealtimeEventParser::RealtimeV2,

codex-rs/core/tests/common/test_codex.rs

@@ -13,6 +13,7 @@ use std::time::Instant;
 use anyhow::Context;
 use anyhow::Result;
 use anyhow::anyhow;
+use codex_config::config_toml::RealtimeWsVersion;
 use codex_core::CodexThread;
 use codex_core::ThreadManager;
 use codex_core::config::Config;
@@ -453,6 +454,7 @@ impl TestCodexBuilder {
             config.model_provider.base_url = Some(base_url_clone);
             config.model_provider.supports_websockets = true;
             config.experimental_realtime_ws_model = Some("realtime-test-model".to_string());
+            config.realtime.version = RealtimeWsVersion::V1;
         }));
         let test_env = TestEnv::local().await?;
         Box::pin(self.build_with_home_and_base_url(base_url, home, /*resume_from*/ None, test_env))

codex-rs/core/tests/suite/realtime_conversation.rs

@@ -360,6 +360,65 @@ async fn conversation_start_audio_text_close_round_trip() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn conversation_start_defaults_to_v2_and_gpt_realtime_1_5() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let api_server = start_mock_server().await;
+    let realtime_server = start_websocket_server(vec![vec![vec![]]]).await;
+    let realtime_base_url = realtime_server.uri().to_string();
+    let mut builder = test_codex().with_config(move |config| {
+        config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+        config.experimental_realtime_ws_startup_context = Some(String::new());
+    });
+    let test = builder.build(&api_server).await?;
+
+    test.codex
+        .submit(Op::RealtimeConversationStart(ConversationStartParams {
+            prompt: Some(Some("backend prompt".to_string())),
+            session_id: None,
+            transport: None,
+            voice: None,
+        }))
+        .await?;
+
+    let started = wait_for_event_match(&test.codex, |msg| match msg {
+        EventMsg::RealtimeConversationStarted(started) => Some(Ok(started.clone())),
+        EventMsg::Error(err) => Some(Err(err.clone())),
+        _ => None,
+    })
+    .await
+    .unwrap_or_else(|err: ErrorEvent| panic!("conversation start failed: {err:?}"));
+
+    assert!(
+        realtime_server
+            .wait_for_handshakes(/*expected*/ 1, Duration::from_secs(2))
+            .await
+    );
+
+    let session_update = realtime_server
+        .wait_for_request(/*connection_index*/ 0, /*request_index*/ 0)
+        .await;
+    let body = session_update.body_json();
+    assert_eq!(
+        json!({
+            "startedVersion": started.version,
+            "handshakeUri": realtime_server.single_handshake().uri(),
+            "voice": body["session"]["audio"]["output"]["voice"],
+            "instructions": body["session"]["instructions"],
+        }),
+        json!({
+            "startedVersion": RealtimeConversationVersion::V2,
+            "handshakeUri": "/v1/realtime?model=gpt-realtime-1.5",
+            "voice": "marin",
+            "instructions": "backend prompt",
+        })
+    );
+
+    realtime_server.shutdown().await;
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn conversation_webrtc_start_posts_generated_session() -> Result<()> {
     skip_if_no_network!(Ok(()));
@@ -393,6 +452,7 @@ async fn conversation_webrtc_start_posts_generated_session() -> Result<()> {
         config.experimental_realtime_ws_model = Some("realtime-test-model".to_string());
         config.experimental_realtime_ws_startup_context = Some("startup context".to_string());
         config.experimental_realtime_ws_base_url = Some(realtime_ws_base_url);
+        config.realtime.version = RealtimeWsVersion::V1;
     });
     let test = builder.build(&server).await?;
 
@@ -718,6 +778,7 @@ async fn conversation_start_connect_failure_emits_realtime_error_only() -> Resul
     let server = start_websocket_server(vec![]).await;
     let mut builder = test_codex().with_config(|config| {
         config.experimental_realtime_ws_base_url = Some("http://127.0.0.1:1".to_string());
+        config.realtime.version = RealtimeWsVersion::V1;
     });
     let test = builder.build_with_websocket_server(&server).await?;
 
@@ -908,6 +969,7 @@ async fn conversation_uses_experimental_realtime_ws_base_url_override() -> Resul
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_websocket_server(&startup_server).await?;
@@ -1279,6 +1341,7 @@ async fn conversation_uses_experimental_realtime_ws_startup_context_override() -
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
             config.experimental_realtime_ws_backend_prompt = Some("prompt from config".to_string());
             config.experimental_realtime_ws_startup_context =
                 Some("custom startup context".to_string());
@@ -1342,6 +1405,7 @@ async fn conversation_disables_realtime_startup_context_with_empty_override() ->
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
             config.experimental_realtime_ws_backend_prompt = Some("prompt from config".to_string());
             config.experimental_realtime_ws_startup_context = Some(String::new());
         }
@@ -1404,6 +1468,7 @@ async fn conversation_start_injects_startup_context_from_thread_history() -> Res
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_websocket_server(&startup_server).await?;
@@ -1466,6 +1531,7 @@ async fn conversation_startup_context_falls_back_to_workspace_map() -> Result<()
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_websocket_server(&startup_server).await?;
@@ -1519,6 +1585,7 @@ async fn conversation_startup_context_is_truncated_and_sent_once_per_start() ->
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_websocket_server(&startup_server).await?;
@@ -1607,6 +1674,7 @@ async fn conversation_mirrors_assistant_message_text_to_realtime_handoff() -> Re
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build(&api_server).await?;
@@ -1735,6 +1803,7 @@ async fn conversation_handoff_persists_across_item_done_until_turn_complete() ->
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_streaming_server(&api_server).await?;
@@ -1878,6 +1947,7 @@ async fn inbound_handoff_request_starts_turn() -> Result<()> {
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build(&api_server).await?;
@@ -1974,6 +2044,7 @@ async fn inbound_handoff_request_uses_active_transcript() -> Result<()> {
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build(&api_server).await?;
@@ -2068,6 +2139,7 @@ async fn inbound_handoff_request_clears_active_transcript_after_each_handoff() -
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build(&api_server).await?;
@@ -2169,6 +2241,7 @@ async fn inbound_conversation_item_does_not_start_turn_and_still_forwards_audio(
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build(&api_server).await?;
@@ -2283,6 +2356,7 @@ async fn delegated_turn_user_role_echo_does_not_redelegate_and_still_forwards_au
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_streaming_server(&api_server).await?;
@@ -2427,6 +2501,7 @@ async fn inbound_handoff_request_does_not_block_realtime_event_forwarding() -> R
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_streaming_server(&api_server).await?;
@@ -2555,6 +2630,7 @@ async fn inbound_handoff_request_steers_active_turn() -> Result<()> {
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_streaming_server(&api_server).await?;
@@ -2698,6 +2774,7 @@ async fn inbound_handoff_request_starts_turn_and_does_not_block_realtime_audio()
         let realtime_base_url = realtime_server.uri().to_string();
         move |config| {
             config.experimental_realtime_ws_base_url = Some(realtime_base_url);
+            config.realtime.version = RealtimeWsVersion::V1;
         }
     });
     let test = builder.build_with_streaming_server(&api_server).await?;