set gpt-5 as default model for Windows users (#4676)

Codex isn’t great yet on Windows outside of WSL, and while we’ve merged
https://github.com/openai/codex/pull/4269 to reduce the repetitive
manual approvals on readonly commands, we’ve noticed that users seem to
have more issues with GPT-5-Codex than with GPT-5 on Windows.

This change makes GPT-5 the default for Windows users while we continue
to improve the CLI harness and model for GPT-5-Codex on Windows.

codex-rs/core/src/config.rs

@@ -46,7 +46,10 @@ use toml_edit::DocumentMut;
 use toml_edit::Item as TomlItem;
 use toml_edit::Table as TomlTable;
 
-const OPENAI_DEFAULT_MODEL: &str = "gpt-5-codex";
+#[cfg(target_os = "windows")]
+pub const OPENAI_DEFAULT_MODEL: &str = "gpt-5";
+#[cfg(not(target_os = "windows"))]
+pub const OPENAI_DEFAULT_MODEL: &str = "gpt-5-codex";
 const OPENAI_DEFAULT_REVIEW_MODEL: &str = "gpt-5-codex";
 pub const GPT_5_CODEX_MEDIUM_MODEL: &str = "gpt-5-codex";
 

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

@@ -17,6 +17,7 @@ use codex_core::NewConversation;
 use codex_core::built_in_model_providers;
 use codex_core::codex::compact::SUMMARIZATION_PROMPT;
 use codex_core::config::Config;
+use codex_core::config::OPENAI_DEFAULT_MODEL;
 use codex_core::protocol::ConversationPathResponseEvent;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::InputItem;
@@ -131,9 +132,10 @@ async fn compact_resume_and_fork_preserve_model_history_view() {
         .as_str()
         .unwrap_or_default()
         .to_string();
+    let expected_model = OPENAI_DEFAULT_MODEL;
     let user_turn_1 = json!(
     {
-      "model": "gpt-5-codex",
+      "model": expected_model,
       "instructions": prompt,
       "input": [
         {
@@ -182,7 +184,7 @@ async fn compact_resume_and_fork_preserve_model_history_view() {
     });
     let compact_1 = json!(
     {
-      "model": "gpt-5-codex",
+      "model": expected_model,
       "instructions": prompt,
       "input": [
         {
@@ -251,7 +253,7 @@ async fn compact_resume_and_fork_preserve_model_history_view() {
     });
     let user_turn_2_after_compact = json!(
     {
-      "model": "gpt-5-codex",
+      "model": expected_model,
       "instructions": prompt,
       "input": [
         {
@@ -316,7 +318,7 @@ SUMMARY_ONLY_CONTEXT"
     });
     let usert_turn_3_after_resume = json!(
     {
-      "model": "gpt-5-codex",
+      "model": expected_model,
       "instructions": prompt,
       "input": [
         {
@@ -401,7 +403,7 @@ SUMMARY_ONLY_CONTEXT"
     });
     let user_turn_3_after_fork = json!(
     {
-      "model": "gpt-5-codex",
+      "model": expected_model,
       "instructions": prompt,
       "input": [
         {

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

@@ -4,6 +4,7 @@ use codex_core::CodexAuth;
 use codex_core::ConversationManager;
 use codex_core::ModelProviderInfo;
 use codex_core::built_in_model_providers;
+use codex_core::config::OPENAI_DEFAULT_MODEL;
 use codex_core::model_family::find_family_for_model;
 use codex_core::protocol::AskForApproval;
 use codex_core::protocol::EventMsg;
@@ -18,6 +19,7 @@ use core_test_support::load_default_config_for_test;
 use core_test_support::load_sse_fixture_with_id;
 use core_test_support::skip_if_no_network;
 use core_test_support::wait_for_event;
+use std::collections::HashMap;
 use tempfile::TempDir;
 use wiremock::Mock;
 use wiremock::MockServer;
@@ -219,13 +221,26 @@ async fn prompt_tools_are_consistent_across_requests() {
 
     // our internal implementation is responsible for keeping tools in sync
     // with the OpenAI schema, so we just verify the tool presence here
-    let expected_tools_names: &[&str] = &[
-        "shell",
-        "update_plan",
-        "apply_patch",
-        "read_file",
-        "view_image",
-    ];
+    let tools_by_model: HashMap<&'static str, Vec<&'static str>> = HashMap::from([
+        (
+            "gpt-5",
+            vec!["shell", "update_plan", "apply_patch", "view_image"],
+        ),
+        (
+            "gpt-5-codex",
+            vec![
+                "shell",
+                "update_plan",
+                "apply_patch",
+                "read_file",
+                "view_image",
+            ],
+        ),
+    ]);
+    let expected_tools_names = tools_by_model
+        .get(OPENAI_DEFAULT_MODEL)
+        .unwrap_or_else(|| panic!("expected tools to be defined for model {OPENAI_DEFAULT_MODEL}"))
+        .as_slice();
     let body0 = requests[0].body_json::<serde_json::Value>().unwrap();
     assert_eq!(
         body0["instructions"],

codex-rs/tui/src/chatwidget/tests.rs

@@ -8,6 +8,7 @@ use codex_core::CodexAuth;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
 use codex_core::config::ConfigToml;
+use codex_core::config::OPENAI_DEFAULT_MODEL;
 use codex_core::protocol::AgentMessageDeltaEvent;
 use codex_core::protocol::AgentMessageEvent;
 use codex_core::protocol::AgentReasoningDeltaEvent;
@@ -1101,6 +1102,11 @@ fn disabled_slash_command_while_task_running_snapshot() {
 
 #[tokio::test]
 async fn binary_size_transcript_snapshot() {
+    // the snapshot in this test depends on gpt-5-codex. Skip for now. We will consider
+    // creating snapshots for other models in the future.
+    if OPENAI_DEFAULT_MODEL != "gpt-5-codex" {
+        return;
+    }
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual();
 
     // Set up a VT100 test terminal to capture ANSI visual output