Propagate Subgraph Extensions in Hive Router

A GraphQL response can carry a top-level extensions object - a free-form map where services attach metadata like cache hints, tracing spans, or warnings alongside data and errors. Until now, Hive Router dropped the extensions returned by your subgraphs.

You can now opt in and propagate them to the client, configured with the new top-level response_extensions block:

response_extensions:
  propagate:
    algorithm: last # first | last | append. default: last
    allow: # optional key whitelist. omit to forward all keys
      - cacheControl
      - warnings

Without this config, behavior is unchanged and nothing is forwarded.

Merging Across Subgraphs

Because a single operation can fan out to multiple subgraphs, the same extension key can show up in several responses. The algorithm setting decides what the client sees:

• last (default) - the last subgraph to respond wins.
• first - the first subgraph to respond wins.
• append - every value is collected into an array, always an array even for a single value.

For example, if subgraph a and b both return extensions.foo, append gives the client every contribution:

{ "extensions": { "foo": [{ "some": ["array"] }, { "some": "object" }] } }

• response_extensions configuration reference