The current arc and chapter are indicated at the beginning of each episode when they are prepublished in Young Animal, that's how we know. That information is also included in the volumes.
Thanks for the quick reply. I didn't realize that Young Animal releases included that info. Good to know.
The reason I asked was because some mangaka reveal that their manga is entering its last arc. I wonder if Miura would do it with Berserk.
I mean sure, these majors events involved Griffith, but with the exception of the battle atop Ganishka, they also involved Guts and Casca. In fact, all three of them involved the Skull Knight and Zodd as well. What I'm trying to say is that since Griffith is the main antagonist, it's not surprising that he's key to these big climactic events.
The reason I included Griffith and not Guts in my question is because of the following.
Guts' story line, at first, was revenge. Then it became to rescue Casca. Then, to take Casca to Elfhelm. And, at last, Casca is healed. This is, of course, just a simplified baseline of Guts' journey so far. And as of Episode 357, the only major thing remaining on Guts' journey is revenge against Griffith. Unless something new pops out, his storyline is ready for the conclusion.
For Griffith it's somewhat different. His major story beats are the Eclipse, Albion, World Spiral Tree. Each being the climax of an arc. All these events come off as methodically planed for something that's going to happen in the future. The God Hand has a plan that it's trying to make into fruition, and according to Guts, Griffith has the same ambition as before, so it's safe to assume that he might have a unique opinion on the matter and his own goals. What this could be is unknown and up for debate and speculation, but the next Griffith story beat is definitely coming. It might be the climax of Fantasia arc, that would move us to the last and conclusive arc of the story, or it might be the endgame, which means that Guts vs Griffith showdown will happen before/during this event.
Long story short, in my opinion Guts' storyline is already ready for the conclusion of the story. Griffiths' storyline still has a bit left. I'm expecting the next few episodes, not sure exactly how many, to reveal what God Hand's endgame is. I'm also expecting to see Skull Knight appear in Elfhelm. He might be the one to reveal this. Maybe though a flashback to 1000 years ago. If this is the case, that this would explain the endgame of the God Hand, give us Skull Knight's backstory, and, most likely, Void's backstory. This is of course mere speculation on my part, but, in my eyes, if we break the story down to 3 simple sections: beginning, middle, and end, then the beginning would be Black Swordsman and Golden Age arcs, middle would be Conviction, Millennium Falcon, and Fantasia so far, plus a bit more setup. I feel like we are very close to the end section of the story. However long it's gonna be, I honestly can't say. But I do see it taking as little as 50 episode and as much as 150.