In the build up to the game, Graham Thomas spoke to Keiran Williams as part of S4C's preview for Judgement Day.
From match-ups to to his new deal, read Keith from Neath's thoughts below.
Keiran Williams has admitted it could be an emotional Judgement Day for the Ospreys on Saturday as he and his teammates brace themselves for a number of departures.
The centre will go up against fellow new Wales squad colleague Mason Grady as the Ospreys attempt to beat Cardiff with a bonus point to pip their great rivals to the Welsh Shield and a place in the Heineken Champions Cup next season.
But it could well prove a bitter-sweet occasion with the long-term futures of some others still up in the air and Stephen Myler, Joe Hawkins and Ethan Roots all confirmed to be moving on.
Williams – who joined Jac Morgan and Morgan Morris in signing a new deal with his region this week – admits the wheel is turning in Swansea, but is demanding that standards still have to improve.
“It’s happened in the past and it’s a fact that we lose people every season,” says the centre who will line-up at the Principality Stadium for a derby that is live on S4C.
“It makes things difficult, but we have to go out and play our best even though we know that players are moving on.
“Hopefully, we can do those players justice, make them proud, and make this game against Cardiff one to remember.
“Personally, I think we still have to do better than we have done in the last season or two. We have to get things right with the squad we put together.
“We didn’t start the season well, but I still think we are the best of the four regions. Hopefully, when the game is over we can point to the table and it will show that.”
Williams was attracting interest from English and French clubs after a season in which he broke into Warren Gatland’s Wales squad for the Six Nations for the first time.
But the 26-year-old insists his decision to extend his time at the region was a straightforward one.
“I’m a home-grown boy from the area and so once I had the deal over the line then it was almost an easy decision to make.
“I recognise that we are going into a challenging time for all four regions, but I don’t see why things can’t improve and I want to be part of that because I have an affiliation with the Ospreys.”
Williams will partner namesake Owen Williams in an attack-minded Ospreys line-up that includes George North and Luke Morgan on the wings and sees the long-awaited first start for Anscombe at outside-half after his recent injury problems.
They will face a Cardiff side who will take the Heineken Champions Cup spot if they pick up a single bonus point.
It should mean a fascinating battle in the back lines between Williams and Grady – although not the direct confrontation most had anticipated.
Centre Grady, who was capped for the first time in the Six Nations, has been moved to the right wing in the absence of injured Josh Adams, with Rey Lee-Lo instead at outside centre.
“It will be good to play against Mason and the other Cardiff boys and then afterwards and the season is over, hopefully we can share a beer,” adds Williams.
“Hopefully, we will be the team that has qualified for the Heineken Cup as it’s a hugely important thing for us to be in that tournament.
“It was a tournament I always watched as a youngster and I’ve loved having the chance to play in it.
“We were disappointed we couldn’t beat Saracens, but the wins against Leicester and Montpellier provided some of the highlights of our season, so it’s a tournament we definitely want to be in again next season.”
S4C: Saturday – 5.00pm: Clwb Rygbi
Ospreys v Cardiff
Live coverage of the URC Judgement Day match from the Principality Stadium, Cardiff.