Do you ensure that the API retrieves only changed data?

Yes, to retrieve only changed data, I would implement incremental data fetching. Common techniques include: 1) Using timestamps or version numbers: the API exposes a 'last_updated' field; the client sends the timestamp of the last sync, and the server returns records newer than that. 2) ETag/Last‑Modified headers: the client stores the ETag from the previous response and includes it in the If‑None‑Match header; the server returns 304 if nothing changed. 3) Change Data Capture (CDC) streams: the backend publishes change events to a message queue or log, and the client consumes only new events. 4) Delta queries: the API accepts a delta parameter and returns only differences. These approaches reduce bandwidth, avoid duplicate processing, and keep the client state consistent.