When you invest with Autumn, you're doing it through Saxo. This means that you create an account in Autumn, and get an investment account at Saxo Markets - but you control everything in the Autumn app.
Your holdings in Autumn portfolios are held in custody accounts with Saxo Markets. Saxo Markets primarily uses its global custodian for securities except for a few exchanges where local requirements make that necessary. The global custodian is currently Citibank and HSBC.
Saxo Markets is a licensed subsidiary of Saxo Bank, and has operated in Singapore since 2006 and serves as the APAC headquarters. It is a leading fintech specialist that connects people to investment opportunities in global capital markets by providing online trading and investment services.