Microsoft's Agent Control Specification is one of the more practical Build 2026 ideas because it targets a gap every serious agent team eventually hits: prompts are not controls. If an AI agent can call tools, write files, update tickets, query internal data, or invoke another agent, the runtime needs a deterministic place to say "allow," "deny," or "modify" before the action reaches the real system.
The naming is still easy to confuse. Microsoft's Build recap calls ACS the Agent Control Specification, the public community site uses Agent Control Standard, and the installable package Effloow Lab tested is @microsoft/agent-governance-sdk@4.0.0, a public-preview TypeScript SDK from the Agent Governance Toolkit. This article uses "ACS-style control" for the pattern and is careful not to claim that every framework-specific adapter is generally available.
Effloow Lab ran a local sandbox PoC for this article. The lab installed the TypeScript SDK, installed the Python agent-governance-toolkit==4.0.0 package in a virtualenv, and used the SDK's GenericFrameworkAdapter to allow one simulated tool call while denying a destructive shell-style action before its handler ran. The evidence note is at data/lab-runs/microsoft-acs-sdk-agent-control-multi-framework-sandbox-poc-2026.md.
