The missile is still under development. Also this is first test from canister I suppose. First time they have released fotos of agni 5 with canister launch. Mirv is already tested with agni 3. Don't expect goi to declare so soon as it will be crossing the Rubicon which can attract sanction and make other nations suspicious about India. Further agni 5 & 6 are completely different family of missiles, these are actually surya 1&2 full blown ICBMs with mirvs Agni 6 will come with minimum 5-7 warheads with above 10000kms range just short of reaching America so as to not annoy uncle. K4 and K5 too are mirved.
There's a reason why chinese are crying as they have lost nuclear blackmailing capability and doklam is a proof where all their threats were countered by similar threats from India and China backed off. Also chinese have toned down and are now talking about CBM and resolving issues through talks and negotiation....
Enjoy the new power status of India which will only keep on improving from here...