https://www.navalnews.com/naval-new...dias-unique-arihant-class-is-still-in-hiding/
Analysis of the few photograph available confirm that some aspects of Arihant bear a strong resemblance to the Kilo Class. The upper sonar dome on top of the bow and many aspects of the sail are visually identical. And the hull diameter appears to match. In essence, the forward hull and sail are essentially similar to the Kilo Class. This makes some sense as India purchased 10 Kilos which are known as the Sindhughosh Class in service.
Overall the arrangement of the system is the same as the Russian systems originally fitted to the Kilo. However the intercept sonars in the trailing edge of the sail are arranged one above the other. This may explain the different shape of the sonar window seen there on the Arihant.
One visible difference between the bow on Arihant and the Kilo Class is the torpedo tube arrangement. Arihant’s are set lower. This indicates some internal differences and confirms that it is not literally a Kilo hull.