All controlled participants must commit to, and in fact, engage in cost sharing transactions. In CSTs, the controlled participants make payments to each other (CST Payments) as appropriate, so that in each taxable year each controlled participant’s IDC share is in proportion to its respective RAB share ...

See paragraph (b)(1)(i) of this section regarding the requirement that controlled participants, as defined in section (j)(1)(i) of this section, share intangible development costs (IDCs) in proportion to their shares of reasonably anticipated benefits (RAB shares) by entering into cost sharing transactions (CSTs) ...