What ACS Actually Is — and How It Relates to AOS
The Naming Confusion
This is worth being precise about, because the two names get used almost interchangeably in vendor content, and there’s a second, unrelated naming collision to watch for.
The Agent Observability Standard (AOS)
- Status: OWASP-incubated open specification (Apache 2.0)
- Hosted at: aos.owasp.org
- GitHub:
trustworthyagentsorganization, mirrored atOWASP/www-project-agent-observability-standard - Definition: Defines the technical contract — the hook methods, event schemas, verdict objects, and extensions to OpenTelemetry, OCSF, CycloneDX, SPDX, and SWID that make an agent “instrumentable, traceable, and inspectable”
The Agent Control Standard (ACS)
- Status: Applied, governance-framed expression of the AOS specification
- Launch: v0.1.0 on May 27, 2026, announced at AI Agent Security Summit in San Francisco
- GitHub:
Agent-Control-Standard/ACS(MIT-licensed) - Definition: The runtime-governance framing, reference architecture (Guardian Agent pattern, three-tier control model), and community push built on top of AOS
The Structural Relationship
ACS as a Fork of AOS
The ACS repository is, structurally, a fork of the OWASP AOS repository:
- The rationale, key components, and version roadmap are close to identical across both projects
- ACS’s own site points back to
aos.owasp.orgas “the Specification” - Licensing differs (Apache 2.0 for the OWASP repo, MIT for the ACS repo)
- Both are community-governed with no single vendor owning the spec
Key Contributors
The initiative is coordinated by contributors including:
- Michael Bargury — co-creator of ACS, co-founder and CTO of Zenity (AI-agent-security firm)
- Rock Lambros — director of AI standards and governance at Zenity
- A broader community of founding contributors
The Launch Philosophy
As Bargury put it at launch:
“Governance cannot rely on soft guardrails or wishful system prompts.”
This statement captures the ACS philosophy: runtime enforcement, not just documentation or guidelines.
The Practical Takeaway
Treat AOS as the Specification
AOS provides the technical foundation:
- Hook methods and event schemas
- Verdict objects and response shapes
- Extensions to OpenTelemetry, OCSF, CycloneDX, SPDX, and SWID
- The “instrumentable, traceable, and inspectable” contract
Treat ACS as the Governance Framing
ACS provides the implementation guidance:
- Reference architecture (Guardian Agent pattern)
- Three-tier control model
- Implementation roadmap and best practices
- Community governance and ecosystem
When You Implement “ACS”
When you implement “ACS,” you are:
- Implementing AOS’s instrument/trace/inspect contract
- With a control-plane mindset
- Following the ACS reference architecture
- Participating in the ACS community governance
The Microsoft Naming Collision
A Separate “Agent Control Specification”
Microsoft introduced its own, similarly-named “Agent Control Specification” as part of its Build 2026 Agent Governance Toolkit:
- Distinct effort with a different set of interception points
- Not affiliated with the OWASP/Zenity-led ACS covered in this guide
- Different architecture and implementation approach
Why This Matters
Some early blog coverage conflates the two, leading to confusion:
| Aspect | OWASP/Zenity ACS | Microsoft ACS |
|---|---|---|
| Governance | Community-led (OWASP, Zenity) | Microsoft-controlled |
| Specification | Built on AOS | Independent specification |
| Licensing | MIT + Apache 2.0 (AOS) | Microsoft’s licensing terms |
| Interception Points | AOS hook methods | Microsoft-defined hooks |
| Ecosystem | Open-source community | Microsoft ecosystem |
Recommendation
When you read vendor material referencing “ACS,” confirm which one is meant:
- Check if it references aos.owasp.org or agentcontrolstandard.org
- Look for mentions of OWASP or Zenity
- Verify the GitHub repository being referenced
AOS vs ACS: A Practical Mapping
| Layer | AOS (Specification) | ACS (Governance) |
|---|---|---|
| Technical Contract | Hook methods, event schemas, verdict objects | Uses AOS specification |
| Observability | OpenTelemetry extensions, OCSF mapping | Implements AOS tracing |
| Inventory | CycloneDX/SPDX/SWID extensions | AgBOM implementation guidance |
| Architecture | Core concepts (Observed Agent, Guardian Agent) | Reference architecture patterns |
| Implementation | Technical definitions | 12-step implementation guide |
| Governance | OWASP community governance | ACS community governance |
| Ecosystem | Framework integrations | Enterprise deployment patterns |
Key Takeaways
- AOS is the specification — the technical contract for making agents instrumentable, traceable, and inspectable
- ACS is the governance framing — the reference architecture and implementation guidance built on AOS
- ACS is structurally a fork of AOS — they share the same technical foundation and roadmap
- The Microsoft naming collision is real — verify which “ACS” vendor material is referencing
- When implementing ACS, you’re implementing AOS — with a control-plane mindset and governance framing
Next Steps
- Three Pillars — understand the core AOS concepts that ACS builds upon
- Three-Tier Architecture — see the ACS reference architecture
- Implementation Guide — follow the step-by-step deployment process