diff --git a/packages/ai/src/providers/openai-codex-responses.ts b/packages/ai/src/providers/openai-codex-responses.ts
index db61ee383..2a15b7bc9 100644
--- a/packages/ai/src/providers/openai-codex-responses.ts
+++ b/packages/ai/src/providers/openai-codex-responses.ts
@@ -2151,14 +2151,29 @@ function recordCodexWebSocketFailure(state: CodexWebSocketSessionState, activate
 	}
 }
 
+function getCodexWebSocketEnvValue(): boolean | undefined {
+	const envVal = $env.PI_CODEX_WEBSOCKET;
+	if (envVal !== undefined) {
+		return $flag("PI_CODEX_WEBSOCKET");
+	}
+	return undefined;
+}
+
 function shouldUseCodexWebSocket(
 	model: Model<"openai-codex-responses">,
 	state: CodexWebSocketSessionState | undefined,
 	preferWebsockets?: boolean,
 ): boolean {
+	// Explicitly disabled by the model or session state.
+	if (model.preferWebsockets === false) return false;
+	// Explicitly disabled by the session state.
 	if (!state || state.disableWebsocket) return false;
+	// Env val > Preference
+	const envVal = getCodexWebSocketEnvValue();
+	if (envVal !== undefined) return envVal;
+	// Negative preference overrides model preference; otherwise use the model's preference.
 	if (preferWebsockets === false) return false;
-	return $flag("PI_CODEX_WEBSOCKET") || preferWebsockets === true || model.preferWebsockets === true;
+	return true;
 }
 
 export interface OpenAICodexTransportDetails {
@@ -2214,10 +2229,13 @@ export function getOpenAICodexTransportDetails(
 		providerSessionState?: Map<string, ProviderSessionState>;
 	},
 ): OpenAICodexTransportDetails {
+	const envVal = getCodexWebSocketEnvValue();
 	const websocketPreferred =
-		options?.preferWebsockets === false
-			? false
-			: $flag("PI_CODEX_WEBSOCKET") || options?.preferWebsockets === true || model.preferWebsockets === true;
+		envVal !== undefined
+			? envVal
+			: options?.preferWebsockets === false
+				? false
+				: options?.preferWebsockets === true || model.preferWebsockets === true;
 	const state = getCodexWebSocketStateForPublicSession(model, options);
 
 	return {