The rumor comes from hardware leaker hongxing2020, who was pretty accurate before, and was spotted originally by Videocardz.com.
3.11 update— hongxing2020 (@hongxing2020) March 11, 2023
The Geforce RTX 4070 could be based on the same AD104 GPU as the RTX 4070 Ti, but pack less SMs, with a total of 5,888 CUDA cores. This is quite less than the RTX 4070 Ti, which has a full enabled AD104 GPU with 7,680, but still, it comes with 12GB of GDDR6 memory on a 192-bit memory interface. The TDP should be set at 200W.
Nvidia CEO, Jensen Huang, will be holding the opening keynote at the GTC on March 21st, so hopefully, we'll hear more about the Geforce lineup as well.