# Combine streaming with backfill

> HyperCore private-preview documentation.

> For the complete documentation index, see [llms.txt](/docs/llms.txt).

<Callout intent="info">
  This API is in private preview. Endpoint availability and response schemas may change before general availability.
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# Combine streaming with backfill

Run a live subscription and persist the cursor plus block height. On reconnect, request replay. If replay fails, backfill the missing block range, dedupe domain events, update the cursor, then resume live delivery.

## Cursor rule
Advance a durable cursor only after downstream storage succeeds. Treat a gap, correction, or finality change as a reason to backfill and reconcile.

## Chain API cross-link

When replay cannot bridge a gap, use [Chain API block backfill](/docs/chains/hyperliquid/hypercore/guides/retrieve-and-backfill-blocks).