It looks like Arista will have two 400g products within 3-4 months.

The quad small factor module sounds promising.  PTK's interposer system architecture uses small form factor and they have been working on the 400g quad pin for some time.

https://www.lightreading.com/optical-ip/400g-terabit/arista-promises-new-400g-switches-for-these-cloudy-times/d/d-id/746993

"The company said the new switches will be priced at under $1,800 per 400G port. The 7060PX4-32, which uses OSFP (Octal Small Form Factor Pluggable) modules, is coming by the end of the year, and the 7060DX4-32, which uses QSFP-DD (Quad Small Form Factor -- Double Density) modules, will be available before the end of March 2019."