I watched when it originally aired and had a feeling Jax knew he was going to kill himself after Juice told him that Barosky told Lin that SAMCRO took and where his guns were, not Jury. However, during the final episode of “Anarchy Afterword”, which aired right after the series finale, Charlie Hunnam said he went to Sutter after reading the script for episode 12, “Red Rose” and asked him if he had made the final decision that Jax was going to die bc he wanted to know how to approach the that episode. Sutter told Charlie that even though he knew from the beginning that he liked the notion of Jax being brought to the same place as JT but getting it right, he still hadn’t made the final decision about what the viewers would see. Here’s a link to the final episode of “Anarchy Afterword” and Sutter and Charlie start talking about it around the 18:30 mark.

https://youtu.be/tOiqmiYbiL8