Originally Posted by
PaulC852
As noted at the link above, if the first flight is on CX then the onward flight can be on any of their partner airlines. And "partner" here means interline partner, which is a much longer list than just the oneworld airlines. (It's more or less every traditional (i.e. not LCC) airline).
Unfortunately, many legacy carriers have moved away from this policy. I recall CX did at one point but backtracked soon after.