Williams has been named in Gatland's 45-man World Cup training squad but the 35-year-old accepts the hard work starts now - via two training camps in Poland and three World Cup warm-up Tests - before Gatland culls 15 players ahead of departure to New Zealand on August 31.
Given that Williams was not required during Wales' recent Six Nations campaign after being overtaken in the openside pecking order by his Cardiff Blues colleague Sam Warburton, it is safe to say the chips are down.
"There is a long summer of training ahead and three pre-World Cup games, so I suppose the slate is clean for everyone," said Williams.
"I am not going to lie - it was a blow missing out on the Six Nations squad because I played well in the autumn (Tests) when I was given the opportunity.
"It's one of those things. You have to take it on the chin and move on. It was more frustrating than disappointing.
"In all likelihood, they will probably only take one openside to the World Cup. There are so many boys who can play at six and seven, so we will have to see what happens."
The World Cup apart - Williams was part of Wales' last three campaigns in 1999, 2003 and 2007 - he currently stands just two appearances short of joining Gareth Thomas and Stephen Jones as his country's third cap centurion.
"To get 100 caps would be the ultimate for me, but if I don't, I don't. I would have taken one cap," he added.
"I look at it as the glass being half-full. I've had a great career, and if I manage to get two more caps, then happy days.
"I think Warren has been spot on in what he has said. He doesn't want to dish out the caps, he wants me to earn them, and I totally agree with him.
"When you are 35 and you have played the amount of rugby I have, you are not going to be as sharp as what you used to be, but I've been happy all season. My form has been pretty good."
Williams though, is under no illusion about Warburton's quality - he captained Wales against the Baa-baas - or that of his fellow back-row young guns Dan Lydiate and Toby Faletau.
"Sam is a special talent, a special player, and he is going to eclipse what most players have done in Wales," Williams said. "He is only going to get better.
"The scary thing about that back-row is that the three of them are still really young.
"The more they play, the better they are going to get, so the future is in safe hands there for many years to come."
Other players in the World Cup back-row mix include Melbourne Rebels' former Gloucester captain Gareth Delve and Sale Sharks' new number eight signing Andy Powell.
Gatland though, is unsure of Powell's availability or that of his Sale colleague Dwayne Peel and Exeter prop Craig Mitchell for the July camps in Spala as English clubs are not set to release their players to Wales until August 4.
On Delve's call-up, Gatland said: "We have watched a few of Gareth's games for the Rebels.
"He has about a month more rugby to go as the Rebels aren't having such a great time, but he has been involved in the (Wales) squad before and is playing in the southern hemisphere and is used to the conditions.
"He has acclimatised, and he may force his way into the 30-man squad."
The most notable omissions from Gatland's initial World Cup party are Ospreys pair Dan Biggar and Ian Gough.
Biggar misses out behind chosen fly-halves Jones, James Hook, Rhys Priestland and the Dragons' Jason Tovey, while 34-year-old Gough has failed to secure one of four second-row slots.
Tovey apart, the other uncapped players in Gatland's preliminary World Cup plans are Scarlets lock Lou Reed and Ospreys flanker Justin Tipuric.
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