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This was registrar level, not nameserver level.

AWS Route 53 provides full registrar services for a while now.

They use Gandi iirc, they are not a registrar themselves.

Sure they are, if you register a .com the registrar is "Amazon Registrar, Inc." since 2016 or so (https://www.icann.org/registrar-reports/accredited-list.html). For some other TLDs, they might outsource it.