The last ones were supposedly contemporary with 688i. But honestly there's absolutely no way to know for certain.
All we can use to clue is the public specs of the sub, it's publicly declared quieting systems, it's shape, and the overall quality of the nation's precision manufacturing ability.
Based on those clues, a 2024s Chinese SSN could be anywhere from around 688i to Virginia noise level. It depends on how well the updated quieting equipment integrates with the older hull, and how much the hull was modified to accommodate it.
Precision manufacturing wise, China is among the top in the world, and the 093B has the expected subsystems of a very quiet submarine. It is however in the "aged" hull about similar age as LA and Akula. But it's impossible to know how much the hull was modernized. If it is "just" modified a little and the improved quieting haphazardly bashed on it, it would be less quiet than if it's heavy modified inside and out to fit the new tech perfectly.
We don't have confident knowledge of 09IIIB's subsystems let alone whether they would be expected to be consistent with that of a "very quiet submarine".
Also being an "aged hull" isn't the biggest inherent issue, rather it is its nature as a double hull submarine which is more significant.
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We can certainly make some estimates and speculation about where PLAN nuclear submarine subsystems might be at these days and how well they can apply them to a double hull submarine of 09III family's size, in context of what relevant precision manufacturing capability they may have for it.
And sure, in the past people have thrown around the possibility of 09IIIA maybe approaching that of a 688-688i in terms of acoustic silencing, and it's not out of the realm of possibility that 09IIIB may advance that a bit further to 688i or even a bit better, but I think it's important for everyone to talk about acoustic silencing with a lot and I mean a LOT of caveats.
IMO if anyone tries to write about nuclear submarine silencing (especially for PLAN boats) without using terms like "speculation" or "guesses" or "estimates" or "hard to confidently say" then they are probably being too confident and they need to be dialed down a few notches.
