Facebook long lived token missing expiry time

I am using below facebook api to exchange access token for long lived token

curl -i -X GET "https://graph.facebook.com/{graph-api-version}/oauth/access_token?       grant_type=fb_exchange_token&               client_id={app-id}&     client_secret={app-secret}&     fb_exchange_token={your-access-token}"  

But response is missing "expires_in", though FB documentation https://developers.facebook.com/docs/facebook-login/guides/access-tokens/get-long-lived/ sample response shows expiry field.

Is this a bug or there is no expiry on fb_exchange_token or i have to assume token will expire in 60 days?