Expansion corpus

OpenAlex’s works come in two corpora. The core is the curated catalog most people mean by “OpenAlex” — more than 320 million works built and matched from Crossref, MAG, PubMed, DataCite, and other trusted sources. The expansion is a larger, rawer layer of about 190 million additional works — mostly datasets and single-repository records that don’t match anything already in the core. Together they’re the all corpus: over 510 million works.

The expansion was added in the November 2025 Walden update, and for a while carried the name XPAC (“Expansion Pack”). You’ll still see “XPAC” in older docs, blog posts, and the is_xpac field name — it means exactly this expansion corpus.

The one thing to know: by default you only see the core. Every works query excludes the expansion unless you ask for it, so if a count looks surprisingly low (or suddenly doubles), the corpus is usually why.

Core, expansion, all

Think of it as three views over the same pile of works:

The corpus selector applies to works only — the other entity types have no expansion, so selecting one there does nothing.

In the REST API

The default is core. Pick a different view with the corpus parameter on any works request:

# Core only (default) — ~320M works
curl "https://api.openalex.org/works"

# All works, core + expansion — ~510M works
curl "https://api.openalex.org/works?corpus=all"

# Only expansion works
curl "https://api.openalex.org/works?corpus=expansion"

corpus composes with everything else — ?filter=has_abstract:true&corpus=all counts abstracts across both corpora. It’s a works-only parameter; the other entity types reject it like any unsupported parameter. Each work also carries an is_xpac boolean, so on a corpus=all request you can still tell which results came from the expansion.

Deprecated legacy controls: older docs and code express the same choice with include_xpac=true (equivalent to corpus=all) and the is_xpac filter (filter=is_xpac:true&include_xpac=true is equivalent to corpus=expansion). Both still work, but they’re deprecated — use corpus= in new code. Don’t mix the two vocabularies: a request that combines corpus= with either legacy control returns an error.

In OQL

In the Query Language, the corpus is a trailing parenthetical on a works query — the underlying selector is corpus, with values core, expansion, and all:

works                          # core (default)
works (expansion corpus)       # only the expansion
works (all corpora)            # core + expansion

Why the expansion is opt-in

Two reasons. Data quality: expansion works have thinner, noisier metadata on average — many are bare repository or DataCite records with little more than a title and an identifier. Quality is improving over time, but it’s well below the core. Stability: silently doubling everyone’s result counts overnight would have broken a lot of queries and dashboards, so the expansion sits behind a flag you turn on deliberately.

If you’re doing careful bibliometrics or want the well-described literature, stay on the core. If you’re casting the widest possible net — hunting for a specific dataset, or measuring total coverage — reach for all. For where these records come from in the first place, see Sources › Repositories and How it’s built.