Deciding a question left open in Montrose Chemical Corp. v. Superior Court (2020) 9 Cal.5th 215, this decision holds that in a case involving coverage for injuries occurring over multiple coverage periods, the insured can reach an excess policy after “vertically” exhausting any primary insurance policies for the same period, but need not exhaust all primary insurance policies “horizontally” over all time periods in which injury occurred. However, the decision remands for the Court of Appeal to decide whether equitable considerations might bar a claim for equitable contribution by a primary insurer (whose policy has not been exhausted) against an excess insurer from a prior period. The insured’s rights to defense and coverage are strictly governed by the policy language, but rights to contribution among insurers on the same risk arise in equity and are governed by equitable considerations instead or in addition to contract language.