This is an unusual development, the thought of the A’s as buyers and the Giants as sellers with Tuesday’s trade deadline approaching.

The A’s have engaged in both pursuits over the years, but most recently, on the road to three straight last-place finishes, they’ve discarded older players for prospects at the deadline with a perpetual look-to-the-distant-future mentality.

The distant future is arriving much quicker than expected.

The Giants have been about the here and now, at least throughout the China Basin era, give or take the dumping of Matt Morris in July 2007 and Ray Durham in July 2008 when they were heading for 90-loss seasons.

But they’re in a new place, idling at .500 with lots of players making lots of money and not exactly showing they’re good enough or healthy enough to leapfrog three teams to win their division or four teams to gain a wild-card berth.

The A’s have won 27 of 36 since mid-June, and the Giants were 8-14 in July, two teams going in different directions on the field and requiring different mind-sets in the front office.

The A’s are riding the wave of Khris Davis, Jed Lowrie and a mighty bullpen that compensates for any rotation deficiencies, and last week’s pickup of Mets closer Jeurys Familia confirmed management has no desire to focus only beyond 2018, refreshingly. That hit home when the A’s parted with two prospects and a million international signing bucks.

The Giants have sent out feelers that they won’t be selling, but their continuing downward trend (six losses in seven games) could be leading to an about-face. Do they stick with the status quo — believing this club can do in the final two months what it hasn’t done all season, then possibly beefing up before Tuesday — or opt to dump contracts?

The latter option would be tough not just because the Giants believe fans wouldn’t tolerate a total rebuild but because several players are near impossible to trade, though the Giants did move Matt Moore, Denard Span, Austin Jackson and Cory Gearrin with an eye on staying beneath the $197 million tax threshold.

None of those players was part of the World Series championship era, making it easier to part with them. They could deal Andrew McCutchen, who’ll be a free agent after the season. Hunter Pence also will be a free agent, though they’d likely need to part with a prized prospect to shed Pence’s salary.

The A’s haven’t been buyers since 2014, when they went for it by acquiring starters Jon Lester, Jeff Samardzija and Jason Hammel, only to barely make the playoffs and bow out in a franchise-flattening wild-card loss in Kansas City. The trades cost the club dearly with the departures of Yoenis Céspedes and Addison Russell, and the playoff letdown led to the Josh Donaldson trade.

The A’s finally have recovered, and suddenly they’re the Amazin’ A’s, a team that’s afraid of no deficit and is at its best in comeback mode. Now it’s time to get even deeper, and perhaps they’ll continue to strengthen the bullpen.

The Familia acquisition is a reminder of 2014 when Billy Beane, David Forst and Co. determined the rotation wouldn’t hold up as is and brought in reinforcements. This year the bullpen might not have continued to endure, considering the workloads of Blake Treinen, Lou Trivino and Yusmeiro Petit, so management added Familia.

Perhaps there’s more to come. The list of starters is thin and pricey — for instance, Chris Archer, Jacob deGrom, Noah Syndergaard, Zack Wheeler, Tyson Ross (remember him?) and the revived Matt Harvey — but there are plenty of relievers on the trade block on teams out of contention.

A sampling: Miami (Kyle Barraclough, Drew Steckenrider and Adam Conley), San Diego (Kirby Yates and Craig Stammen), Cincinnati (Raisel Iglesias), Baltimore (Brad Brach) and Texas (Keone Kela).

The Giants need an offensive boost, especially in the outfield, and Baltimore’s Adam Jones, Detroit’s Nicholas Castellanos, Miami’s Derek Dietrich and Texas’ Shin-Soo Choo are available. Dare we add Cincinnati’s Adam Duvall? We dare not. The former Giant’s numbers dramatically dropped this year.

Then again, Larry Baer, Brian Sabean and Bobby Evans could decide not to add at the deadline. Last July, amid rumors several players could be exiting, all the Giants did was send Eduardo Nuñez to Boston for prospects.

If the Giants are more aggressive with moving parts and the A’s continue to be aggressive adding parts, we’d experience a titanic shift in Bay Area baseball.

Around the majors

•The Diamondbacks got one-upped at their own game. Last July they acquired J.D. Martinez from Detroit at the deadline and rode him to the postseason, and now the Dodgers are banking on doing the same with Manny Machado, acquired from the Orioles in a deal that L.A. pitcher Ross Stripling said would be “demoralizing” for other NL West teams. The Diamondbacks were said to be pursuing Machado but settled for left-side infielder Eduardo Escobar, still an upgrade at either short or third. The streaking Rockies, so far, have added relievers Seunghwan Oh and Santiago Casilla (released by A’s) and would do themselves a favor by landing a front-end starter even though their rotation ERA is sub-3.00 the past month. In the AL West, the Astros are set up nicely for the postseason but, like other contenders, could use another reliever. The Mariners would like more depth in both the rotation and bullpen, but their biggest addition could come with the mid-August return of Robinson Cano, though he’ll be ineligible for the playoffs because of his PED bust.

•Either A’s shortstop Marcus Semien has dramatically improved defensively, or advanced defensive metrics aren’t a great indicator. According to the Society for American Baseball Research, Semien has a 7.4 defensive-index ranking (as of Monday), the fifth highest among American Leaguers at all positions. Meantime, Giants shortstop Brandon Crawford, a Gold Glover three straight years, has a 6.6 ranking, 13th highest in the National League. How is that possible? In Semien’s last full season, 2016, his index was 0.0 compared with Crawford’s 15.6. In 2015, Semien’s was -2.3 compared with Crawford’s 15.4. Semien doesn’t have Crawford’s arm, range or hands, at least based on my eye test, which must be failing me.

John Shea is The San Francisco Chronicle’s national baseball writer. Email: jshea@sfchronicle.com Twitter: @JohnSheaHey