The Multi-Model Margin Curve: Why AI Infrastructure Choice Sets Agency Gross Margin

AI infrastructure is no longer a build-versus-buy decision for agencies; it is a margin decision. Every point of provider concentration raises the cost of a client retainer the moment a model's pricing, rate limits, or safety guardrails shift, and 83% of B2C marketers already treat agent capability as a baseline expectation rather than a differentiator. Agencies that route work across multiple providers and gateways protect retainer economics; those that standardize on one API inherit that vendor's roadmap as their own risk profile.