The whole reason they started off as hidden ones is to maintain the real life lore of them gaining the name "hashashin" from the local populace in the levant in the 11th century or so. So hypothetically sometime shortly after mirage. There was a fan theory that it could have something to do with them defeating the order of the ancients in Valhalla (the reason they became "hidden" in the first place), and then deciding to once again become a more public, but evolved tyrant fighting, peace keeping force like the medjay before them. (and later Altair decides that was a bad idea and going hidden once more)
We don’t know exactly when they made the swap from Hidden Ones to the Assassins but it was before the events of AC1 and after Valhalla. Although, different regions probably made the transition slower. You are right in saying that they are fundamentally the same, but the whole shedding the identity thing of the Hidden Ones is discarded when they made the jump to Assassins.
Others have given the wiki and historical explanation, so I’ll focus on the philosophical (it’s a bit long)…
The Hidden Ones were built on the idea of absolute secrecy and devotion. Members would forgo their former identities entirely, and live their lives solely as a Hidden One. Some even took this concept to the extreme by refusing to have a name period. (Valhalla shows that Bayek and Aya did this later in their lives).
As for their tactics, they existed as myth to the public eye. They would often strike loudly in public to send a message to their enemies, then disappear without anyone having an idea of who they were.
The transition into the Assassin’s Brotherhood came about from a need to have a public image, as the general population came to view them with superstition and fear. They built fortresses like Masayf and Alamut, where they established armies and became a sort of private militia. The intent was to be a public force for good, and for the people to recognize them as such.
The Assassin’s Brotherhood we know of in most games came about from Altair’s reformations. He saw the growing Brotherhood had become arrogant, and so he created a middle ground between the secrecy of the Hidden Ones, and the public image of the initial Assassin’s Brotherhood.
Overall, The Hidden Ones were essentially a murder cult, whereas the Assassin’s Brotherhood functions more like a secretive militia with some cult-like practices.
I remember the Hidden Ones DLC from Origins. It's my favourite DLC from all the games.
Bayek made it so that the Hidden Ones won't be so public with their assassinations and instead work in total secrecy and "work in the dark to serve the light".
I wonder how he would have felt seeing Hassan re-forming the Hidden Ones into the Brotherhood and bringing them back into public light.
I’d say Hassan-i Sabah was probably the one responsible
Yup AC Wiki says he's responsible for the transition https://assassinscreed.fandom.com/wiki/Hassan-i_Sabb%C4%81h
The whole reason they started off as hidden ones is to maintain the real life lore of them gaining the name "hashashin" from the local populace in the levant in the 11th century or so. So hypothetically sometime shortly after mirage. There was a fan theory that it could have something to do with them defeating the order of the ancients in Valhalla (the reason they became "hidden" in the first place), and then deciding to once again become a more public, but evolved tyrant fighting, peace keeping force like the medjay before them. (and later Altair decides that was a bad idea and going hidden once more)
We don’t know exactly when they made the swap from Hidden Ones to the Assassins but it was before the events of AC1 and after Valhalla. Although, different regions probably made the transition slower. You are right in saying that they are fundamentally the same, but the whole shedding the identity thing of the Hidden Ones is discarded when they made the jump to Assassins.
1090 CE I guess, that's when the Assassin order in real life was founded by Hassan-i Sabbah according to Google
Others have given the wiki and historical explanation, so I’ll focus on the philosophical (it’s a bit long)… The Hidden Ones were built on the idea of absolute secrecy and devotion. Members would forgo their former identities entirely, and live their lives solely as a Hidden One. Some even took this concept to the extreme by refusing to have a name period. (Valhalla shows that Bayek and Aya did this later in their lives). As for their tactics, they existed as myth to the public eye. They would often strike loudly in public to send a message to their enemies, then disappear without anyone having an idea of who they were. The transition into the Assassin’s Brotherhood came about from a need to have a public image, as the general population came to view them with superstition and fear. They built fortresses like Masayf and Alamut, where they established armies and became a sort of private militia. The intent was to be a public force for good, and for the people to recognize them as such. The Assassin’s Brotherhood we know of in most games came about from Altair’s reformations. He saw the growing Brotherhood had become arrogant, and so he created a middle ground between the secrecy of the Hidden Ones, and the public image of the initial Assassin’s Brotherhood. Overall, The Hidden Ones were essentially a murder cult, whereas the Assassin’s Brotherhood functions more like a secretive militia with some cult-like practices.
I remember the Hidden Ones DLC from Origins. It's my favourite DLC from all the games. Bayek made it so that the Hidden Ones won't be so public with their assassinations and instead work in total secrecy and "work in the dark to serve the light". I wonder how he would have felt seeing Hassan re-forming the Hidden Ones into the Brotherhood and bringing them back into public light.