The old 2-port probe can't measure below 25mOhms. This is because it's a 2 (3) point contact, not 4 point Kelvin. The new one is a 4 point contact Kelvin probe. The old one is 1X and the new one is available in different attenuation, for measuring higher voltage and/or higher impedance. The new probe also uses PDN cable for greatly improved ground loop reduction and external noise shielding.
The old 1-port probe uses a pivot ground for variable pitch and is 1.3GHz. The new probe is 14GHz to support our (and other manufacturers’) 10.5GHz TDR. The new probe is available in different pitches. The old probe is 1X and the new one is available in 1X and also different attenuation. The new probe also uses PDN cable for greatly improved ground loop reduction and external noise shielding.
Both old probes include DC blocks; the new ones don't, but the new ones include a calibration board.
The new 2-port probe will be available Nov/Dec 2020. The new 1-port probe will be available Jan/Feb 2021. https://www.picotest.com/products_PDN_Probe.html