​The Athletics selected Jamie Arnold in the first round of the 2025 MLB Draft with the 11th overall pick out of Florida State, and he ended up ranked as the A’s No. 2 prospect for much of the season, until 2026 first-rounder Drew Burress took that spot. Still, Arnold is viewed as a top-100 prospect in the game, ranked No. 57 by MLB Pipeline. The A’s were aggressive with his starting point in the pros, sending him out to Double-A Midland to begin the season. Outside of a rough month of May where he posted a 7.11 ERA and a 2.13 WHIP across 25 ⅓ innings, Arnold has been tremendous. His second-highest ERA in any other month has been the 3.54 he posted in five July starts. On the year, he has a 6-5 record with a 3.67 ERA and a 1.45 WHIP across 108 innings. In each of his last four appearances, Arnold has gone at least 5 ⅔ innings, giving up three runs in two starts and not allowing an earned run in the other two. Over those 23 ⅓ innings, he has struck out 31 batters and walked just four. In his last two, he hasn’t allowed a single free pass. This is the kind of stretch late in a season that could see him earn a promotion to Triple-A Las Vegas before the end of the year to give him some tangible experience of pitching in that ballpark to take into the offseason. On A’s Cast this week, Arnold was asked about his changeup, which he said is essential for any successful lefty in the big leagues to pair with a good fastball. “I’ve been working on [the changeup] all year and it’s really come together since the All-Star break,” Arnold said. “I’ve settled with a grip that I like.” He also mentioned that he estimated he threw it about 13 times in his previous start, getting four or five whiffs and keeping the pitch in the zone. The success matches up with the timeline of when he seemed to unlock his changeup this season. Right now the focus is to keep building the trust he has in the pitch and the confidence to throw it in any situation. That’s going to be one of the bigger development points for him in the minors. Arnold has also been working on locking in his routine since the break, which is another key piece of any player’s development. This is a facet of the game that isn’t talked about as much, but one that players mention consistently as a key to getting them ready every day. That routine helps keep them ready over the course of a grueling season. “It’s been a learning experience,” Arnold said of his first year in pro ball. “It’s a longer season and you’re facing better competition on a daily basis. I’ve learned a ton. I’ve gotten my [stuff] kicked in a couple of times, but I learned from it and just try to move forward.”