On February 15, 2022, Michael Amundsen posted this thread at the BGG Abstract Games Forum. Here's part of the design notes that came with it:
It's no secret that this game was inspired by Meridians and Go. More precisely, it was inspired by a finite Go variant I wanted Luis' opinion on. He quite quickly came to realize that the game could be at once simplified and made into something more than a Go variant. I had actually thought about the very change he suggested, but I had dismissed it because it seemed to make for a less interesting game. I'm very happy to say he showed me wrong. This is one of those situations that illustrate the important difference between having an idea and recognizing its worth.

Anyway, the change was to the capture condition: Instead of tightly surrounding a group (Go's capture condition), it's enough to cut it off from other groups – to loosely surround it, so to speak. This is of course extremely similar to the brilliant idea Kanare had for the capture condition in Meridians. Simply change that game's definition of a path, so it doesn't have to be a straight line.

The hex grid (as opposed to the square grid) is interesting in that you more often need to connect your own groups in order to cut your opponent's groups from each other. This creates an interesting dilemma, and makes securing life far from trivial.

After some 3 months of lively discussion, Luis was confident to state:
For what it's worth, Michael and I think Lifeline is the best game either of us has designed.

Need we say more ...

Lifeline © 2022, Michael Amundsen and Luis Bolaños Mures