---
title: "Derived per-ETF filing-cadence net flow estimate (creation/redemption proxy)"
method: GET
path: "/api/v1/etf/{symbol}/flows"
tags: ["Funds & ETFs"]
---

# Derived per-ETF filing-cadence net flow estimate (creation/redemption proxy)

`GET /api/v1/etf/{symbol}/flows`

Derived endpoint that computes per-ETF net flow estimates for one ETF over the requested lookback window by walking the ETF snapshot history and emitting ONE period per CHANGE of the SEC-derived (aum_usd, nav) pair. Formula per period: ``net_flow = Δ(shares_outstanding) × to_nav`` where ``shares_outstanding = aum_usd / nav``, ``from_date`` is the last snapshot carrying the old pair and ``to_date`` is the first snapshot carrying the new pair. This is the standard ETF creation/redemption proxy used by analysts; results are an ESTIMATE, not ICI-authoritative numbers. Snapshot aum_usd/nav derive from SEC filings (NPORT-P monthly, 485BPOS annual) and are constant between filings, so flows are reported on FILING CADENCE, not per calendar day (the previous per-day contract read 0.0 on every non-filing day). Consecutive snapshots with unchanged (aum_usd, nav) are a single plateau and produce NO entry. When fewer than 2 distinct plateaus exist in the window the response is 200 with ``period_flows=[]`` and ``total_net_flow_dollar_estimate=null`` (honest 'no change observed', not an error) - and since API-1.9 the BODY says why: ``reason`` (``single_filing_plateau`` / ``no_computable_shares``), ``plateaus_observed``, and the backing filing's ``rep_pd_date`` + ``accession``. Days where the snapshot blob is missing are silently skipped; plateaus span across missing dates. Use case: ``UC-3 Sector Rotation Detector`` per-ETF accumulation signal, complemented by ICI aggregate at /etf/flows/aggregate. BREAKING (DATA-N4.7.1): this endpoint replaced the per-calendar-day ``series`` contract with filing-cadence ``period_flows``, and renamed the ``days`` query param to ``lookback_days``. The old ``days`` param is SILENTLY IGNORED (FastAPI drops undeclared query params; it is not rejected) - a mid-migration client sending ``?days=30`` gets 200 with the default lookback window.

## Path parameters

- `symbol` string, required — ETF ticker.

## Query parameters

- `lookback_days` integer — Lookback window in days (1..90, default 90). Bounded by the 90-day ETF snapshot retention - a wider window can never hold more data (dated snapshots are swept after 90 days). Out-of-range returns 400. NOTE: the pre-DATA-N4.7.1 param `days` is no longer declared, so it is silently ignored, not rejected.

## Response `200`

Per-symbol derived filing-cadence period flows + total.

- EnvelopeEtfPerSymbolFlowsPayload
  - `data` EtfPerSymbolFlowsPayload, required — Derived per-ETF filing-cadence net flow estimates over the ETF snapshot. Methodology: standard ETF creation/redemption proxy. Period net flow = Δ(shares_outstanding) × to_nav where shares = aum_usd / nav. Periods are bounded by the snapshot dates where the SEC-derived (aum_usd, nav) pair CHANGED, NOT by calendar days - because snapshot aum_usd/nav derive from SEC filings (NPORT-P monthly, 485BPOS annual) and are constant between filings. Computing per calendar day produced 0.0 on every non-filing day, which was misleading; filing-cadence periods report the real step. Caveats (echoed in `methodology` field): - Period boundaries are filing-refresh dates, NOT daily creation/redemption activity. Treat each period as one aggregate creation/redemption signal spanning the filing interval. - ETF snapshots report prior-day close NAV. - Estimate is NOT ICI-authoritative (ICI member-only ETF data publishes monthly per-asset-class, not per-symbol). - Days where the symbol's snapshot blob is missing are skipped (sparse time-series); plateaus span across missing dates transparently.
    - `symbol` string, required — ETF ticker.
    - `lookback_days` integer, required — Echoed scanned window length in days.
    - `snapshots_available` integer, required — Count of dated ETF snapshots successfully loaded within the window (<= lookback_days).
    - `period_flows` EtfPerSymbolFlowPeriod[], required — Filing-cadence periods oldest-to-newest, one per (aum_usd, nav) change. Empty list when fewer than 2 distinct plateaus exist in the window (honest 'no change observed', NOT an error).
      - `from_date` string, required — Last snapshot date carrying the prior (aum_usd, nav) pair (YYYY-MM-DD).
      - `to_date` string, required — First snapshot date carrying the new (aum_usd, nav) pair (YYYY-MM-DD).
      - `from_nav` number, nullable — NAV per share on from_date.
      - `to_nav` number, nullable — NAV per share on to_date (used in the net-flow formula).
      - `delta_shares` number, nullable — shares(to_date) - shares(from_date) where shares = aum_usd / nav. Positive = net creations, negative = net redemptions.
      - `net_flow_dollar_estimate` number, nullable — Derived period net flow estimate = delta_shares * to_nav, rounded to 2 dp. Positive = net creations, negative = net redemptions.
    - `total_net_flow_dollar_estimate` number, nullable — Sum of net_flow_dollar_estimate across period_flows. Null when period_flows is empty.
    - `reason` string, nullable — API-1.9: machine-readable cause of an EMPTY period_flows, so a client can tell 'no data by domain law' from 'broken pipeline' without reading OpenAPI prose. `single_filing_plateau` = the window held exactly one distinct (aum_usd, nav) filing plateau and EVERY loaded snapshot was computable (fewer than the 2 plateaus a flow period needs - quarterly NPORT-P inputs make this the NORMAL state between filings, not an error). `plateau_with_unusable_snapshots` = one plateau exists but the window also holds loaded snapshots that could not yield shares (any position - head, interior, or tail), so 'the filing did not change' is NOT established across the window. `no_computable_shares` = snapshots loaded but no (aum_usd, nav) pair yielded a shares-outstanding estimate. Days with no snapshot blob at all remain transparent (sparse series). Null whenever period_flows is non-empty.
    - `plateaus_observed` integer, required — Distinct (aum_usd, nav) filing plateaus observed in the window. A flow period needs at least 2; 1 means the SEC inputs did not change across the window (see `reason`).
    - `snapshots_unusable` integer, required — Loaded snapshots whose (aum_usd, nav) could not yield a shares-outstanding estimate (missing / zero / negative / non-finite inputs). They are excluded from plateau detection and disclosed here - skipped data is declared, never silent.
    - `rep_pd_date` string, nullable — Reporting period date of the SEC filing backing the newest COMPUTABLE snapshot in the window (from that snapshot's _sources.holdings) - the snapshot that actually took part in plateau detection. Null when no computable snapshot carries provenance. When flows are empty this is the filing the single plateau rests on - the next filing is what ends it.
    - `accession` string, nullable — SEC accession number (dashed format) of that same backing filing. Null when the snapshot carries no holdings provenance.
    - `methodology` string, required — Plain-English description of the formula + filing-cadence period semantics + non-ICI-authoritative disclaimer.
  - `meta` SugraMeta, required — Metadata attached to every /api/v1/* response envelope.
    - `endpoint` string, required — Requested endpoint path.
    - `data_time` string, required — ISO 8601 UTC timestamp of the source data, not of the request.
    - `response_time` string, required — ISO 8601 UTC timestamp when this response was produced.
    - `provider` string, required — API name and version.
    - `source` string, nullable — Identifier of the primary upstream source used for this response.
    - `attribution` string, nullable — Human-readable attribution mandated by an upstream source (e.g. a securities regulator or self-regulatory organization). Present only on responses whose source requires the owner and source to be clearly identified. Do not remove or alter it when using the response.
    - `fallback_used` boolean, nullable — True when the primary source failed and a fallback produced the data.
    - `fallback_chain` string[], nullable — Ordered list of sources attempted, in the order they were tried.
    - `cached` boolean, nullable — True when this response was served from the internal cache.
    - `stale` boolean, nullable — True when the cached response was returned after the upstream rate-limited or errored. Clients can use this to detect degraded data.

## Other responses

- `401` — Missing or invalid `x-api-key` header. JSON body with a stable `code` distinguishing `missing_api_key` (no header sent) from `invalid_api_key` (header sent, key not accepted); any other 401 source carries the generic `unauthorized` with its detail as `reason`. Plus `hint`. `plan` is always null on 401 - an unauthenticated request has no plan; quota exhaustion is 429, not 401.
- `422` — Validation Error
- `429` — Daily rate limit exceeded. Check `X-RateLimit-Reset` for the next window.
- `503` — Upstream source is temporarily unavailable. Retry after a short delay.

---

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