CSMS 66390093 is a U.S. Customs and Border Protection (CBP) Cargo Systems Messaging Service bulletin (system update), published on September 30, 2025. It carries the official CBP guidance brokers and importers must follow for the topic — "ACE Certification Standard Invasive Maintenance Window on October 1, 2025 from 5:00 p.m. ET to 8:00 p.m. ET". CSMS messages are the operational layer between Commerce determinations and at-the-border collections: when Commerce publishes a new rate, scope ruling, or instruction, CBP turns it into a CSMS that ACE/ACS systems and brokers act on.
Full text as published by U.S. Customs and Border Protection
CSMS 66390093 is a U.S. Customs and Border Protection (CBP) Cargo Systems Messaging Service bulletin titled "ACE Certification Standard Invasive Maintenance Window on October 1, 2025 from 5:00 p.m. ET to 8:00 p.m. ET". CSMS bulletins are the operational instructions CBP issues to brokers, importers, and ACE filers covering rate changes, system updates, scope guidance, and other day-to-day customs-operations changes.
CBP published CSMS 66390093 on September 30, 2025. The bulletin's instructions are typically operative as of the publication date unless the body specifies a different effective date.
Yes — for at-the-border filing and entry collection. CSMS messages translate Commerce's Federal Register determinations into operational CBP instructions that ACE/ACS systems and brokers execute. The Federal Register notice is the underlying legal authority; the CSMS is the operational implementation. Both should be read together when reconciling a rate or scope change.
Tandom guides relevant to CBP CSMS messages
How to subscribe to CBP Cargo Systems Messaging Service and triage the messages that change broker filing behavior, without losing the ones that matter.
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Set up alerts when a CBP CSMS message changes a duty rate on an HTS code you depend on. Built for brokers, forwarders, and importer compliance teams.
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Cash deposit cascade, separate rates, all-others, and PRC-wide rates. Worked example on case A-570-910 (galvanized welded steel pipe from China) with three exporter-specific rates.
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