Hey as per my idea K family of missiles is known as Black Project in DRDO and here I am giving you its details

About DRDO
The Defence Research and Development Organisation is an agency of the Republic of India, charged with the military's research and development, headquartered in New Delhi, India.

Black Project
The K family of missiles is a series of submarine-launched ballistic missiles (SLBM) developed by India to boost its second-strike capabilities and thus the nuclear deterrence. Information about this family of missiles has mostly been kept classified.
"The classified 'K' missile family" is known as the "Black Project" which DRDO officials are covertly working on.
It is reported that "the top secret indigenous "K" missiles are faster, lighter and stealthier.

Types of Missiles
K-15 SLBM
K-4 Mark I (Agni-III MRBM)
K-4 Mark II (Agni-V ICBM)
Air Launched
K-5 SLBM (Agni-VI ICBM)