As you can see, Instagram's adding comment threads, making it easier to see what each comment relates to within the comment stream.
As explained by Instagram:
"Now, when you hit reply underneath any comment, your response will automatically be grouped right underneath it in a thread."
The change was first highlighted in testing by Mashable back in June - and it makes sense, particularly given the amount of account tagging that goes on in the comments of Instagram posts, and on other platforms, these days.
Facebook's always looking to find more ways to get people sharing and engaging more often, and smaller design tweaks like this are one of the most effective, and simplest ways for them to do so. Rather than having to tweak the feed algorithm or update a process, changes like this align with user behaviors and help to clarify the process.
That's not to say any design change of an app with 700 million users is easy, and won't come without criticism, but the underlying logic makes sense.
The new replied are available as part of Instagram version 24 and above for iOS and Android, and will be available globally in the coming weeks.