Defining the Three Architectures
Enterprise teams deploying AI agents generally choose between three enforcement architectures, and the distinction matters because it determines where policy decisions actually happen. A gateway architecture places enforcement at a shared network point that all agent traffic passes through before reaching tools, models, or external services. A sidecar architecture places enforcement in a process that runs alongside each workload, typically in the same pod or host, intercepting traffic locally rather than centrally. An SDK architecture places enforcement inside the application itself, as a library that the agent code calls directly when making tool or model requests. Each model answers the same question, where should policy be checked, with a different tradeoff between centralization and proximity to the workload.
Identity, Least Privilege, and Audit Across Models
Enforcing least privilege and maintaining an audit trail depend on where policy decisions are made and how consistently that point sees traffic. A gateway can apply consistent identity checks and permission scoping across every agent that routes through it, and because logs originate from one place, audit evidence is easier to centralize and review. The tradeoff is that a gateway only sees what passes through it, so any tool call made outside that path is invisible to the enforcement layer. A sidecar keeps enforcement close to the workload, which can capture local calls a gateway would miss, but audit and identity data is now distributed across many instances, requiring aggregation before it is useful for compliance review. An SDK ties enforcement directly to the calling code, which can enable fine-grained permission checks tied to the specific function or agent making the request, but it depends entirely on developers calling the SDK correctly and consistently, and audit logging quality is only as good as what each integration actually emits. In multi-tool or multi-model environments, this difference compounds, since agents rarely follow a single, uniform code path.