Updated and Revised CT Penal Code linked below prefaces the guide providing the Crime (CGS) for Conspiracy as (CGS § 53a-51). See pg 2.
However, under a multi-charge conviction, and if the offender
can be punished as if they were the principal offender, perhaps the applicable
Mandatory Minimum of Class A Murder (53a-54a) or
25 years will be applied at sentencing-- not withstanding the Class A offense to Class B Felony default instruction (one to 20 years punishment).
I'm finding the language about Conspiracy for any Class A offense defaulting to a Class B Felony unclear, given the purpose of Conspiracy pursuant to (CGS § 53a-51) is to prevent the offender from being punished more for a lesser Classed offense than punished for Murder (53a-54a) which is conceivable since punishment under Class B Felony can be as little as one year but not more than 20!