This document describes a cloud bidding method and system for DSPs, agencies, and technical advertisers, providing all the advantages of owning a bidder, such as deploying first party data and models for bidding and creative selection, with none of the infrastructure overhead or data security concerns. The advertiser only focuses on the data and models, while cloud bidding takes care of bid request ingestion, targeting, impression tracking, budgeting, pacing, creative filtering, logging, reporting, billing and more. The cloud bidding system includes a Multi-Tenant Bidder (MTB) which enables lean bidding by hosting many “tenant” bidders. The MTB receives and ingests callouts from a number of advertising exchanges (e.g., SSPs), applies targeting, budgeting, and pacing, and requests bids by invoking custom bidding functions (campaign endpoints) for each of the eligible advertiser “tenants.”