diff --git a/codex-rs/core/src/auth.rs b/codex-rs/core/src/auth.rs
index fb4114a7c2..a4f85c8377 100644
--- a/codex-rs/core/src/auth.rs
+++ b/codex-rs/core/src/auth.rs
@@ -534,12 +534,21 @@ fn load_auth(
     };
 
     // API key via env var takes precedence over any other auth method.
-    if enable_codex_api_key_env && let Some(api_key) = read_codex_api_key_from_env() {
-        let client = crate::default_client::create_client();
-        return Ok(Some(CodexAuth::from_api_key_with_client(
-            api_key.as_str(),
-            client,
-        )));
+    if enable_codex_api_key_env {
+        if let Some(api_key) = read_codex_api_key_from_env() {
+            let client = crate::default_client::create_client();
+            return Ok(Some(CodexAuth::from_api_key_with_client(
+                api_key.as_str(),
+                client,
+            )));
+        }
+        if let Some(api_key) = read_openai_api_key_from_env() {
+            let client = crate::default_client::create_client();
+            return Ok(Some(CodexAuth::from_api_key_with_client(
+                api_key.as_str(),
+                client,
+            )));
+        }
     }
 
     // External ChatGPT auth tokens live in the in-memory (ephemeral) store. Always check this
@@ -1527,6 +1536,14 @@ mod tests {
             }
             Self { key, original }
         }
+
+        fn unset(key: &'static str) -> Self {
+            let original = env::var_os(key);
+            unsafe {
+                env::remove_var(key);
+            }
+            Self { key, original }
+        }
     }
 
     #[cfg(test)]
@@ -1638,6 +1655,20 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    #[serial(codex_api_key)]
+    async fn load_auth_prefers_openai_api_key_env() {
+        let _codex_guard = EnvVarGuard::unset(CODEX_API_KEY_ENV_VAR);
+        let _openai_guard = EnvVarGuard::set(OPENAI_API_KEY_ENV_VAR, "sk-openai");
+        let codex_home = tempdir().unwrap();
+
+        let auth = super::load_auth(codex_home.path(), true, AuthCredentialsStoreMode::File)
+            .expect("load auth")
+            .expect("auth available");
+
+        assert_eq!(auth.api_key(), Some("sk-openai"));
+    }
+
     #[test]
     fn plan_type_maps_known_plan() {
         let codex_home = tempdir().unwrap();