Two acronyms, two programs, and one persistent source of confusion. While they sound like siblings, a 3PAO and a C3PAO serve different masters, enforce different standards, and operate under entirely different regulatory umbrellas. Using the wrong one isn't just a typo, it's a compliance dead end.
This guide separates the two, explains when you need each, and provides the 10 hard-hitting questions most vendor-selection guides skip.
A 3PAO is an independent organization that validates a Cloud Service Provider's (CSP) security controls against FedRAMP baselines derived from NIST SP 800-53 Rev. 5. They execute the Security Assessment Plan (SAP), produce the Security Assessment Report (SAR), and document residual risk. The CSP then uses the SAR to build a Plan of Action and Milestones (POA&M) and submit the authorization package to a sponsoring federal agency and the FedRAMP PMO.
A C3PAO is authorized by The Cyber AB specifically for the Department of Defense (DoD) supply chain. They assess contractors against the 110 requirements of NIST SP 800-171 Rev. 2 under CMMC Level 2.
The decision depends on who you sell to and what data you handle.
The overlap is real but the assessors are not shared. Public control-mapping analyses estimate roughly 50% overlap between the 800-53 and 800-171 control sets. That means evidence can be reused across programs, but the assessments themselves must be conducted separately by their respective authorized organizations.
If you need both, plan the evidence architecture once and map it to both frameworks. Duplication of evidence collection is the avoidable cost. Duplication of assessments is not.
Don't pick an assessor based on brand prestige alone. Use these questions to evaluate fit and capacity before you sign.
Print this list. Bring it to every call. The assessor who answers all 10 without hesitation is the one who has done this before.
Even with the right assessor, first-time assessments often fail for predictable reasons:
For a deeper look at the habits that keep teams audit-ready year-round, see Mycroft's guide to continuous compliance monitoring and compliance automation for startups.
Your tooling choice is a direct cost lever on the assessment itself. Assessing six separate point tools is manual, slow, and expensive. The assessor bills for reconciling log formats, retention periods, scan cadences, and API export structures across every system.
By using a platform like Mycroft to unify cloud security, application security, device management, vulnerability scanning, and compliance automation, your evidence is already structured, timestamped, and cross-mapped to the control families your 3PAO or C3PAO needs to test. Controls map once across FedRAMP, CMMC, SOC 2, ISO 27001, HIPAA, and GDPR and stay mapped through continuous compliance monitoring.
Preparation is not a shortcut; it's a defense. By structuring evidence upstream, you ensure the assessment downstream runs clean, fast, and within budget.
3PAO and C3PAO selection is not about logos on a slide deck. Pick based on four criteria: volume of comparable assessments, independence posture, team stability, and tooling alignment. Start with the FedRAMP Marketplace for 3PAOs and the Cyber AB Marketplace for C3PAOs. Filter by assessment volume, then run the 10-question interview from this article.
See how Mycroft's cross-mapped evidence layer reduces 3PAO reassessment friction.
Can the same firm serve as both a 3PAO and a C3PAO?
Yes, some firms hold both designations. Coalfire, Schellman, and A-LIGN are recognized FedRAMP 3PAOs and authorized CMMC C3PAOs. However, the assessments are separate engagements under separate accreditation programs. Having one firm handle both can simplify scheduling but does not reduce the number of assessments required.
How long does a FedRAMP 3PAO assessment typically take?
Initial FedRAMP authorization assessments typically run 6 to 12 months from readiness review through agency ATO, depending on system complexity and agency engagement. The 3PAO assessment phase itself (SAP through SAR delivery) often takes 8 to 16 weeks. Annual reassessments are shorter because the 3PAO tests a subset of controls plus one-third of the remaining control set each year.
What is the difference between A2LA and the Cyber AB?
A2LA (American Association for Laboratory Accreditation) accredits FedRAMP 3PAOs against ISO/IEC 17020:2012 and FedRAMP-specific requirements. The Cyber AB is the sole accreditation body for the CMMC program, authorizing C3PAOs to conduct CMMC Level 2 assessments. Different bodies, different programs, different accreditation standards.
Do I need a sponsoring agency before engaging a 3PAO?
For FedRAMP authorization, yes. Without an engaged sponsoring agency, the only path forward is FedRAMP Ready status, which is a readiness designation, not an authorization. An active sponsor reviews your security package and ultimately grants the Authority to Operate (ATO). Secure the sponsor before contracting the 3PAO.
Can evidence collected for FedRAMP be reused for CMMC?
Partially. NIST SP 800-171 (CMMC's control foundation) derives from NIST SP 800-53 (FedRAMP's control foundation), with roughly 50% overlap in control requirements. Evidence for overlapping controls can be reused, but each program requires its own formal assessment by its authorized assessor type. Plan your evidence architecture to serve both frameworks from a single source of truth.
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