The 30-year-old, whose previous deal had been due to expire at the end of this campaign, had been in talks with the club for some time before the extension was made official on Monday.
The Alavés captain enters his tenth season with the club, having become an undisputed presence between the posts over the last four campaigns after initially playing second fiddle to Fernando Pacheco.
Sivera arrived in Vitoria from Valencia in 2017 and has made 179 appearances for Alavés, a tally he now has the time and opportunity to add to significantly under his extended contract. Should he see out the full length of the new deal, the goalkeeper from Jávea would reach 13 seasons as an Alavés player — a landmark no one else has achieved in the club's history.
At 30, Sivera remained a figure who could plausibly have attracted offers from elsewhere in La Liga given his form over recent seasons, but he opted to prioritise the trust the club has consistently shown him and his own sense of being a fundamental piece of the project.
His previous extension, in December 2023, had been agreed under similarly cordial circumstances, underlining a relationship both parties have been keen to preserve.
Alavés were acutely aware that two key players had contracts expiring in 2027: Sivera and midfielder Antonio Blanco. The club never contemplated losing either man, despite the risk of seeing them leave for nothing next summer.
With Sivera now committed long-term, the sporting director's office will turn its full attention to retaining Blanco, a considerably more complicated task given his profile has attracted attention from clubs with greater financial resources.
Sivera's path to becoming Alavés's undisputed number one was far from straightforward. After arriving from Valencia, he spent a season on loan at Almería before returning to Vitoria, where he had to wait behind Pacheco for his opportunity.
That chance came during the 2022-23 campaign, with Alavés then in the second division, when then-coach Luis García Plaza handed him the gloves. Sivera repaid the faith shown in him by playing a central role in the club's promotion back to the top flight, appearing in 45 matches that season and never looking back since.
The club described Sivera as "one of the footballers who best represents the identity" of Alavés in its statement confirming the renewal, highlighting his saves, regularity and capacity to appear at decisive moments.