Will it support only "basic" DynamoDB features (reading/writing records) or some "advanced" things too, like GSIs/LSIs, streams, fine-grained access control, TTLs, backups?
GSI, LSI are fully supported already.
Backup is fully supported too (but not identical to DynamoDB).
TTL is in final development mode.
So yes, everything is planned to be fully supported
1. Scylla added Alternator Streams as an experimental feature in Scylla Open Source 4.3: https://www.scylladb.com/product/release-notes/scylla-open-s...
2. You can read about the current state of compatibility here:
https://scylla.docs.scylladb.com/master/alternator/compatibi...