Concepts (deprecated)

Deprecated. Concepts are superseded by Topics, OpenAlex’s current subject-classification system. The concepts endpoints and the concepts field on works still work, but concepts are frozen — no longer recomputed or expanded — so new works are not tagged with them and the concept tree is not maintained. Use topics (and the aboutness hierarchy of domains, fields, and subfields) for anything new. This page is kept for the many links and workflows that still point at it.

A concept is a subject tag from OpenAlex’s original, now-deprecated classification: a hierarchical taxonomy of research areas — Computer science, Machine learning, Citation — inherited from the Microsoft Academic Graph (MAG) and linked to Wikidata. There are about 65,000 concepts, arranged in six levels from broad (level: 0, e.g. Computer science) to narrow (level: 5). A concept’s OpenAlex ID looks like C41008148; fetch one at api.openalex.org/concepts/C41008148.

How we build it

Concepts came out of the Microsoft Academic Graph, whose final open dataset OpenAlex adopted when MAG was discontinued in 2021. Each concept maps to a Wikidata item, which supplied its description, image, and multilingual labels. Concepts were arranged into a tree — every concept records its ancestors (broader concepts above it) and related_concepts (siblings and neighbors) — and works were tagged with concepts by a machine-learning classifier that read each work’s title, abstract, and other metadata, emitting a score per concept. Because ancestors of a tagged concept were also attached, a work’s concepts list often included broad, low-scoring entries.

This scheme was retired because it was hard to maintain and its accuracy was uneven, especially at the deeper levels. In 2024 OpenAlex replaced it with topics — a cleaner, curated four-level aboutness hierarchy (domains → fields → subfields → topics) that classifies each work more reliably. Concepts are now frozen: the tree is no longer expanded, and derived fields such as counts_by_year, summary_stats, ancestors, and related_concepts are no longer recomputed and are typically null on the live objects. See Aboutness for how the successor signals compare.

Fields

This is the canonical dictionary of every field on a concept object. Fields shared with other entities are documented once on Common fields; concept-specific notes are below. As noted above, several fields are no longer maintained and may come back empty.

id

String. The OpenAlex ID for this concept, e.g. https://openalex.org/C41008148. See Common fields.

wikidata

String. The Wikidata ID for this concept, as a URL, e.g. https://www.wikidata.org/wiki/Q21198. Wikidata is the canonical external ID for concepts — every concept has one.

display_name

String. The concept’s name, e.g. Computer science. See Common fields.

level

Integer. The concept’s depth in the tree, from 0 (broadest, e.g. Medicine) to 5 (most specific). Level-0 concepts have no ancestors.

description

String. A short description of the concept, taken from its Wikidata item.

ids

Object. All known external identifiers for this concept, as URIs where possible; keys with no value are omitted. Concept-specific keys: openalex, wikidata, mag (Microsoft Academic Graph integer ID), wikipedia, umls_aui, and umls_cui (Unified Medical Language System identifiers). See Common fields.

image_url

String. A URL to a representative image for the concept (usually the lead image of its Wikipedia article).

image_thumbnail_url

String. A URL to a smaller (thumbnail) version of image_url, handy for icons.

international

Object. The concept’s display_name and description translated into many languages, keyed by language code. No longer maintained — usually an empty object on live concepts.

ancestors

List. Dehydrated concept objects for the broader concepts above this one in the tree (id, wikidata, display_name, level). No longer recomputed — typically null on live concepts.

related_concepts

List. Dehydrated concept objects for concepts frequently co-occurring with this one (id, wikidata, display_name, level, score). No longer recomputed — typically null on live concepts.

works_count

Integer. The number of works tagged with this concept. See Common fields.

cited_by_count

Integer. The total citations received by all works tagged with this concept. See Common fields.

summary_stats

Object. Precomputed bibliometric indicators (2yr_mean_citedness, h_index, i10_index). See Common fields. No longer recomputed — typically null on live concepts.

counts_by_year

List. Works and citation counts for roughly the last ten years, one element per year. See Common fields. No longer recomputed — typically null on live concepts.

works_api_url

String. A ready-made Works API URL returning every work tagged with this concept, e.g. https://api.openalex.org/works?filter=concepts.id:41008148. A convenience link — the same query you’d build with the concepts.id filter.

created_date

String. The date this concept was added to OpenAlex (YYYY-MM-DD). See Common fields.

updated_date

String. The ISO 8601 UTC timestamp of the last change to this concept object. See Common fields.

In the API

Concepts are deprecated. The endpoint below still works but is frozen and will not receive updates — use topics instead.

The Concepts endpoint is at api.openalex.org/concepts. Fetch a single concept by ID — /concepts/C41008148 — or a list, and filter, search, sort, group, and page over the fields above.

To find the works carrying a concept, filter on the Works endpoint:

https://api.openalex.org/works?filter=concepts.id:C41008148

For the full list of filterable, sortable, and groupable fields see the Concepts API reference; for all endpoints see the endpoints index.