This looks quite good for Cox's. Interestingly, according to Wikipedia it has not previously been observed in breeding plumage, and so this may be the first photo of one having carried out at least some pre-breeding moult.
There doesn't seem to have been much published on this hybrid since the paper that investigated DNA to confirm it was the result of a pairing between male Pec Sand and female Curlew Sand:
https://sora.unm.edu/sites/default/files/journals/condor/v098n03/p0459-p0463.pdf
Images of a juvenile photographed in Japan were published in Birding World in 2002 15 (8): 346–347.
GeoffC
