I believe there is a continuity between open and polyamorous relationships. You can start in an open relationship that eventually becomes a polyamorous one. For some, having “sex first” (see note  below) is the opening for possible polyamorous relationships (except for those which have no sexual possibilities).
Is it easy to separate polyamorous from open relationships? Author Penelope Jones prefers poly to open and sees a distinction:
In an open relationship it is likely that all partners may never meet, and it’s also likely that love will never be involved in the majority of the relationships outside of the primary couple. Open relationships on a normal level usually involve casual hook-ups and/or friendships that have sexual tendencies. This is not what a Polyamorous life is.
Polyamory is described as Loving many or having the capability to love many people, in many different ways. Polyamorous normally doesn’t mean casual hook-ups; it does mean love is involved. Partners are normally introduced soon after dating commences. Everyone in the ‘family’ normally is involved with one another on some level of intimacy. Remember— intimacy doesn’t have to mean sex!
Ms. Jones appears to drawing a line in the sand with open relationships on one side and polyamory on the other. I have yet to meet polyamorous people who did not have some open relationship(s) within their group. That is, within a poly group, one or more members may have open relationships with others outside the group from time to time. When I was ‘upset’ (i.e. jealous) about my partners having affairs with other women in our apartment, they suggested I read Tristan Taormino’s “Opening Up“. Her advice, I recall, was that when you feel jealous, move on to an open relationship yourself. So when my partners tell me “we’re going to have xxx over for the night”, they mean I’m free to play with one of my ‘friends’.
In mixed polyamorous and open relationships, those in the open relationship need to determine what to communicate to your other partners about your affairs. Here are two opinions:
I like to be told when a partner has sex with someone else: in a scene, with someone they recently met, or with another partner. I’d just like to be told about it. Kind of up-front and forthcoming.
I like to be told about it because it helps to remove a sensation of anxiety that I have about the unknown.
…being told about their sexual encounters (or even coffee dates!) helps keep anxiety at bay and indirectly describes who is becoming more important in their lives
Annelle Wright commented to his post:
I wouldn’t want my partner to routinely feel anxious if they didn’t know what happened. I’d be happier about sharing that level of detail for their sexual gratification, solely for their sexual gratification, with the consent of other partners. I’d seek consent from regular partners anyway
For steady ‘friends’, my partners say something as benign as “I’m going to be with xxx” . Usually we know “xxx” (because we have been introduced). If it’s a one-night stand or a trip to the back of the bar, we have a ‘get acquainted’ meeting.
Although we can make an intellectual distinction between polyamorous and open relationships, in practice those in polyamorous ones must keep their partners informed of the status of their open affairs. How much to inform depends on your partners needs. It helps to communicate early on to minimize their possible rejection of a prospective addition to their poly family, or to enable them to share intimacies with your ‘friend-with-benefits’.
For us it is counterproductive to reaching fulfillment in alternative lifestyles to think polyamory is superior/preferrable to open relationships . There are many who might consider an open relationship but are daunted by polyamory. Open relationships can and often do lead to polyamory.
 sex-first: PV has this requirement in her new relationship checklist:
Want to have sex on the first night, and not judge me for wanting the same.
Sexual compatibility is crucial to me, and I’d like to find that out sooner rather than later. I also see nothing wrong with sex on the first night, so I go ahead and do it whenever the circumstances allow it. If me having sex with you on the first night disqualifies me to be your girlfriend/wife in your mind, your mind is obviously not open and evolved enough to warrant my interest.