- Bats Right, Throws Right
- Height 6' 8", Weight 260 lb.
He struggled in the 2012 European Junior Championship Qualifier with three walks, one hit and two runs (both earned) while retiring no one.  He also attended the MLB European Academy that year.  He was 3-2 with a 3.03 ERA for the 2013 Leksand Lumberjacks, tying Blake Eager, Per Sjörs and Paul Waterman for 8th in the Elitserien in wins. 
He fell to 1-3 in 2014 with a 10.25 ERA for Leksand and Akademin.  He was 1-2 with a 3.50 ERA for the London Cavaliers in Collegiate Baseball League Europe.  He still made Sweden's team for the 2014 European Championship; Arvid Carlstedt was Sweden's only younger pitcher. He debuted against Italy, relieving Kent Karlsson in the 4th with a 7-1 deficit. He began by walking Alex Sambucci on four pitches. He fanned Mario Chiarini but Alberto Mineo doubled and Mattia Reginato grounded in a run. He escaped further harm by getting Erick Epifano on a grounder. In the 5th, he was wild, walking Stefano De Simoni and Juan Carlos Infante. Gabriele Ermini flew out then Jakob threw a wild pitch. Alessandro Vaglio hit into a run-scoring error and Syrén walked Sambucci and Chiarini to force in another run, 10-1. He escaped the bases-loaded jam by getting Mineo and Reginato on flies. He then went 1-2-3 in the 6th, then was relieved by Emil Sahlin. His other outing was closing out a 12-8 loss to Germany, relieving Sahlin and serving as Sweden's top hurler of the day (2 1/3 IP, 4 H, 1 BB, 1 R, 1 ER, 2 K). 
In 2015, he rebounded to 1-1, 2.55 for Akademin.  In the 2015 B-Level European Championship, he went the distance to beat Lithuania (9 H, 5 BB, 4 R, 3 ER); he was third in the event in ERA, behind future major leaguer Dean Kremer and Marek Deska. 
He did not pitch in the '16 Elitserien and allowed one run in 7 2/3 for the Rättvik Butchers.  He then played for De Glaskoning Twins in the Netherlands. In the 2018 Hoofdklasse, he was 1-1 with a save and a 2.74 ERA, though he walked 18 in 23 innings.
The big right-hander next signed with Germany's Solingen Alligators. In 2019, he had no decisions but four saves and fanned 19 in 16 2/3 IP, with a 1.62 ERA; he added 5 1/3 shutout innings in the postseason. He led the loop in saves.  He was back with the Swedish team for the 2019 European Championship; Sweden went winless. They had a chance against Israel, leading 3-2 in the 9th when he relieved Nicklas Melin. He gave up hits to Nick Rickles and former major leaguer Danny Valencia. Simon Rosenbaum drew a full-count walk to load the bases. A wild pitch scored PR Assaf Lowengart with the tying run. He intentionally walked Rob Paller and finally got an out, fanning Zach Penprase, but then walked Jeremy Wolf on four pitches to force in the losing run. He made three appearances in the 2019 Euros but struggled (2 1/3 IP, 8 H, 6 R, 6 ER, 6 BB, 2 K); only Erik Marquardsen had a higher ERA for the Swedes. 
He was back south in 2021, with Quick Amersfoort in the Netherlands.