> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/faq/help-topics/webhook/large-payloads-and-chunking/track-chunked-backfill-via-reference.md).

# How do I know when a chunked backfill is complete?

**Large or chunked requests are announced by two notification events before the data arrives:**

* a `large_request_processing` event
* a `large_request_sending` event, the one to track. It includes `expected_payloads`, telling you how many chunks to expect.

Each subsequent chunk carries a `terra-reference` header beginning with that same reference plus colon-separated metadata such as chunk numbering (for example `{INITIAL_UUID}:chunk:{CHUNK_ID}`).

**Group all chunks by the shared reference, and use `expected_payloads` to know when the backfill is complete.**

These marker events fire only for explicit API backfills exceeding a one-month range. Passive auto-syncs deliver directly to the standard data folders/endpoints. See the [event types reference](https://docs.tryterra.co/reference/health-and-fitness-api/event-types).