"I know what I want the final story to be and where I want these people to end up in the end," creator Jason Rothenberg said Sunday at TCA.

The 100 returns for season three in January after one of The CW series' bloodiest, and most ambitious, episodes to date.

The season-two finale of the series saw one of the show's leading ladies, Clarke (Eliza Taylor), forced to kill to save her own people. Creator Jason Rothenberg admits it was an uphill battle both onscreen and off.

"We try to create impossible choices all the time," he told reporters Sunday at the Television Critics Association's winter press tour. "Last season, I knew that that moment of choice was going to come for Clarke at the end and where she was going to have to pull the lever or not and kill all of Mount Weather to save her people. We could have gone a little bit easier and saved the kids, but I was like — and this was a standards and practices nightmare — but I wanted to see the cost of it and I wanted people to feel the cost of it."

Despite the battle with standards and practices behind the scenes, Rothenberg has embraced that part of his job on the series thus far.

"I'm more surprised by the notes that we don’t get than by the notes that we do get," he said. "I feel like one of our jobs creatively is to push the envelope for them, for the network, for broadcast television, and I'm happy to do it."

The 100 will continue to test boundaries and expectations in season three, as it delves more into the world of the grounders and introduce new societies.

"One of the things I love to do is expand the world, so we've obviously done that a lot in the first three seasons," said Rothenberg. "But at the same time, the show started with the 100 wanting to kill each other, and could they overcome their internal conflict before the threat of the Grounders wiped them out? Last year, we introduced some new elements and the conflict was a little more external.

"This season we get into, I think, a bigger version of where the show started, which is there's internal conflict," he continued. "There's a new group that comes in that really mixes things up and creates a lot of conflict internally. We get to know a lot about the Grounder clans, and there's a civil war brewing there too, so, again, it's about, can these people overcome their internal stuff in time to avoid a bigger catastrophe?"

When asked about diving into the Grounders, Rothenberg said he was inspired by Game of Thrones and other shows that are able to continue plot threads from early episodes while also exploring completely new territories as they age. "The world-building of it is one of the things that I like the most just creatively, and allowing us to expand the playing field the way we have keeps it alive," he said.

Speaking about the life of the show and how long he envisions it running, Rothenberg already has a few ideas in mind. "I know what I want the final story to be and where I want these people to end up in the end," he said. "I don’t know how long that’s going to take. I'm not going to sit here and say that I want to do the show as long I can do it. I want do to the show for as long as it interesting to me."

However, he sounds optimistic at least about a fourth season. "Lord willing, we get a season four. We have a good idea of what we want that story to be," said Rothenberg. "If they said, 'This is it. Wrap it up,' we could make this idea I have right now for the wrap-up happen at the end of season four, or five or eight."

The 100 returns Thursday, Jan. 21, at 9 p.m. ET/PT on The CW.