REDUCE COLLECT is gated behind the server's unstable features flag; the feature and its API may be subject to change.

COLLECT is an FT.AGGREGATE reducer that gathers per-document projections within a GROUPBY group and returns them as an array of per-entry maps under the reducer alias, optionally sorted and bounded.

The server does not expose it by default: it must be enabled explicitly, for example via

CONFIG SET search-enable-unstable-features yes

In a cluster the coordinator fans the query out to every shard, so the flag must be enabled on all nodes rather than only the one a given connection happens to route to. Without it, the server replies with an error.

The corresponding library feature must also be considered subject to change:

1. Existing bindings may cease working correctly if the underlying server API changes.
2. Changes to the server API may require changes to the library API, manifesting in either/both of build-time or run-time breaks.

Because the server itself still classes this as an unstable feature, such changes are rather more likely here than for a feature that has simply not been out for long. If you acknowledge this, you can suppress this warning by adding the following to your csproj file:

<NoWarn>$(NoWarn);NRS003</NoWarn>

or more granularly / locally in C#:

#pragma warning disable NRS003