[update] Transport for NSW has announced the changes:
T1 Northern Line
- Current services between Hornsby and the City via Chatswood will be replaced by limited stop services via Strathfield. These services will start or terminate at Central during peak times. At all other times, trains will directly connect to Wynyard, Town Hall and North Shore stations via Strathfield and Central.
- Most Normanhurst to Cheltenham customers travelling to the CBD in the morning peak will have faster or similar journey times compared with today.
- Two extra services per hour in the morning peak and a doubling of trains in the evening peak for Rhodes, Meadowbank and West Ryde.
- All peak hour services to operate as eight car trains to improve capacity and comfort for all T1 Northern Line customer
Read more about this here.