The Everton Twitter account relayed the news of Sigurdsson's departure from the Liberty Stadium:
"Hopefully I will continue to create goals and score goals for the team and contribute to the kind of success we’re seeking at the club," the Iceland international told the Toffees' official website.
"This is an ambitious club and it is clear we are moving in a really good direction. The most important thing is that this team keeps winning games and climbing the table—and does that throughout the season."
As noted, Everton have been massive spenders in the summer transfer window:
The loss of Sigurdsson will be a big blow for the Swans, but he will add a huge amount to the Toffees' central-midfield department.
An accomplished No. 10, the 27-year-old can also drop deep, operate on the flanks or play as a forward if need be.
Though he endured a somewhat underwhelming two-season spell at Tottenham Hotspur, Sigurdsson has proved to be a consistently excellent goalscorer and provider in his two stints at Swansea.
In his time in the Premier League with the Welsh club, he netted 34 goals and provided 29 assists in 124 appearances, per WhoScored.com.
A free-kick specialist, Sigurdsson boasts a stinging right foot, and his linkup play is excellent.
He has also proved himself on the international stage, playing a key role in Iceland's unexpected run to the UEFA Euro 2016 quarter-finals.
In Sigurdsson, Everton have signed a high-quality attacking player and a consistent performer who is only just reaching his peak and should be a huge asset for manager Ronald Koeman as his side push to breach the Premier League's top four in 2017-18.
He should act as a fine replacement for Ross Barkley, who has long been expected to leave Goodison Park, per the Guardian's Andy Hunter.
Indeed, former Everton midfielder Don Hutchison believes Sigurdsson will be an upgrade on the England international, per ESPN UK:
Koeman will hope his latest signing can hit the ground running, as Everton need to make a strong start to the 2017-18 term if they are to compete for the top four.