Proxmox 5.1 is installing Ceph 10.2.5

it's my sources.list file:
Code:
deb http://ftp.nl.debian.org/debian stretch main contrib

deb http://download.proxmox.com/debian/pve stretch pve-no-subscription
# security updates
deb http://security.debian.org stretch/updates main contrib
But installed ceph is 10.2.5
 
Perhaps something has changed recently.

Browsing http://download.proxmox.com/debian/pve/dists/stretch/pve-no-subscription/binary-amd64/ I don't see any ceph packages. I'm still running Proxmox4 so I can't truly comment from experience. But the ceph packages appear to be here: http://download.proxmox.com/debian/ceph-luminous/dists/stretch/main/binary-amd64/ ... that would mean you'd need a sources.list entry of:

deb http://download.proxmox.com/debian/ceph-luminous stretch main

I don't see anything that specifically says this change occurred, but seems to be the case.
 
There is no change recently (since 5.1). The command "pveceph install --version luminous" configures the Proxmox VE Ceph repository - see docs.