SANTA CLARA >> George Kittle, in a half-joking way, refers to them as Optional Training Activities.

Officially, the NFL dubs them Organized Team Activities, and they begin this week for the 49ers. They indeed are voluntary for the three sessions this week and three next week, before mandatory minicamp June 10-11.

Kittle, the 49ers’ ninth-year tight end, raves about the camaraderie in and around the locker room this time of the offseason. It is the first time since 2019 that he’s been a full-time participant at 49ers HQ rather than work out at his offseason home in the Nashville area.

“Besides being on a really good, winning team late in the season and going to the playoffs, one of the best vibes is during the spring for football,” Kittle said at last week’s Dwight Clark Legacy Series in San Jose. “Because you don’t have the pressure of a game that weekend. You have four workouts and get a three-day weekend, so the vibes are elite and immaculate. Everyone is having a good time. There’s such great energy in the building.”

Unlike the previous five weeks, OTA practices allow for 11-on-11 action, but contact (and shoulder pads) remain off limits until training camp in late July. As is the case with half the league, the 49ers are scheduled to use only six of their allotted 10 OTA days.

Here are 10 areas to watch:

1. DEFENSIVE LINE ROTATION >> This is the offseason’s most overhauled unit, so it bears constant scrutiny to see how the newcomers (and a few holdovers) blend with Nick Bosa. Second-round pick Alfred Collins watched but did not participate in the rookie minicamp three weeks ago. Two veteran defensive ends, Drake Jackson and Alex Barrett, have exited since then.

2. SALEH’S AURA >> This is the media’s first chance to see defensive coordinator Robert Saleh work on the field with his unit — for the first time since the 2020 season, that is. Eight years ago, it was fun watching Saleh as a first-time coordinator match up in spring practices and camp against Kyle Shanahan.

3. RUNNING MEN >> Christian McCaffrey’s level of participation is always worth monitoring. But he is an expectant father with potential paternity leave this summer, so attention should shift toward his backups instead. We’ll look more so at them as potential receivers since tackling is not permitted until camp. How does Isaac Guerendo look as a potential third-down back, and how are the hands of rookies Jordan James and Corey Kiner? Are they in the right position for pass protection?

4. OFFENSIVE LINE OPTIONS >> An overlooked competition this year is among the offensive tackles. If Trent Williams isn’t up for these six voluntary OTA practices, who mans the left tackle spot? After an apparent deal with D.J. Humphries fell through, the 49ers added Andre Dillard and Nicolas Petit-Frere to compete with Austen Pleasants and Spencer Burford.

No pads, so no real competition to examine, but we’ll see who might be in the lead as the swing tackle, as well as at left guard, where Ben Bartch and Nick Zakelj figure to battle for Aaron Banks’ old job.

5. LINEBACKER CREW >> Fred Warner has a new contract (three-year extension) and a potential new wingman in rookie Nick Martin, a third-round pick. If Dee Winters has a say, it’s time to show he can be more assignment sound. And if Luke Barrett is more than a special-teams ace, we could see him factor into the linebacker mix here, with the same said for Tatum Bethune and Jalen Graham.

6. WIDE RECEIVER PROSPECTS >> While Brandon Aiyuk does his ACL rehab on the side, the 49ers need to see what kind of connection Brock Purdy has with other wide receivers beyond Jauan Jennings. Ricky Pearsall, last year’s first-round pick, is the most intriguing after his strong finish last year. Jacob Cowing, after a four-catch rookie season, can show the strides he’s made. Demarcus Robinson makes his public debut, but rookies Jordan Watkins and Isaiah Neyor are fascinating projects.

7. SAFETY IN CHARGE >> Ji’Ayir Brown and George Odum are the 49ers’ most experienced safeties, but these OTAs offer a chance to get a first impression of veteran additions Jason Pinnock and Richie Grant. Communication and play-making range will be worth monitoring from all options; Malik Mustapha is amid ACL recovery, and Talanoa Hufanga is in Denver.

8. TIGHT END DEPTH >> Two tight-end sets again should be en vogue this season after the 49ers’ offseason investments in Kittle and free agent Luke Farrell, the latter of whom is a blocking specialist. Aside from observing Farrell’s onboarding process, the 49ers have familiar faces to study: Ross Dwelley, Brayden Willis, Jake Tonges, and Mason Pline.

9. GREEN LIGHT? >> Renardo Green’s seven starts as a rookie make the 2024 second-round pick the odds-on favorite to replace Charvarius Ward at cornerback and pair with Deommodore Lenoir. The greater mystery at cornerback is whether rookie Upton Stout is immediately ready to serve as the Day 1 nickel back, or if that job could be pursued by Chase Lucas or Darrell Luter Jr.

10. QB WATCH >> This is Brock Purdy’s show. He has a new understudy in Mac Jones, who’ll be making his first throws in 49ers’ OTA action — four years after the 49ers’ bypassed him for Trey Lance with the No. 3 overall pick.

If Purdy, Jones or Tanner Mordecai have an off-day, odds are they’ll get a pep talk from Kittle, who added about OTAs: “It’s just going to work, getting great hard work with your teammates, learning some stuff in the meeting room, then you get a three-day break to take a step back, and by the time Monday hits, you’re, ‘Oh, I’m ready to go again.’ ”