As spotted by Anandtech, these two chips eat at the lowest-end of the CPU hierarchy and are likely binned chips that otherwise do not meet Intel’s requirements for operating as higher-rated parts. Being U-series parts, they are intended to operate in low-power mobile applications, such as thin and light laptops. Both carry TDPs of 15W.
The Pentium Gold 6405U does use Hyper-Threading on both of its cores and lists a base frequency of 2.4 GHz.
Pentium and Celeron chips typically do not get Intel’s Turbo Boost feature. Given that the other (Core i3, i5, & i7) Comet Lake U-series chips have lower base frequencies but very high turbo clocks, it's possible that the Celeron 5205U and Pentium Gold 6405U don't have a turbo frequency at all. Intel didn't provide boost information for either chip.
|Intel Celeron 5205U||Intel Pentium 6405U|
|Cores||2 cores||2 core / 4 threads|
|Base Clock||1.9 GHz||2.4 GHz|
|PCI-Express||12 PCIe 2.0 lanes||12 PCIe 2.0 lanes|
The MSRP for the chips is $107 for the Celeron 5205U and $161 for the Pentium Gold 6405U. That being said, they'll probably go from Intel to its vendor partners for notably less.