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Part of the Cyc technology was released, starting in 2001, as OpenCyc, which provided an API, RDF endpoint, and data dump, under appropriate Apache and Creative Commons open source licenses. Its distribution was discontinued in early 2017 because such “fragmenting” led to divergence, and led to confusion amongst its users and the technical community generally that that OpenCyc fragment was Cyc. Those wishing access to the latest version of the Cyc technology today should contact to obtain a research license or a commercial license to Cyc itself. Information about ResearchCyc can be found here and EnterpriseCyc here.

The OpenCyc Platform is your gateway to the full power of Cyc, the world's largest and most complete general knowledge base and commonsense reasoning engine. OpenCyc contains hundreds of thousands of Cyc terms organized in a carefully designed ontology. Cycorp offers this ontology at no cost and encourages you to make use of, and extend, this ontology rather than starting your own from scratch. OpenCyc can be used as the basis of a wide variety of intelligent applications such as:

  • rich domain modeling
  • semantic data integration
  • text understanding
  • domain-specific expert systems
  • game AIs
  • to name just a few.

Release 4.0 of OpenCyc includes:

The core Cyc ontology whose domain is all of human consensus reality. The current release includes:

  • ~239,000 terms (up from ~177,000 terms in the previous release)
  • ~2,093,000 triples (up from ~1,500,000 in the previous release)

Select class (direct and indirect) instance counts:

  • 'place': ~19,000

  • 'organization': ~26,000

  • 'predicate': ~22,000

  • 'business related thing': ~28,000

  • 'person': ~12,700

  • n ~69,000 owl:sameAs links to external (non-Cyc) semantic data namespaces:

    • DBpedia: ~47,000 links, including 696 links to the DBpedia ontology
    • UMBEL: ~21,000 links
    • WordNet: ~11,000 links
    • Wikicompany: 1028 links
    • CIA World Factbook: 172 links
    • RDFAbout SEC company identifiers: 661 links
    • RDFAbout states and counties: 71 links
    • FOAF: 44 links
  • English strings (a canonical one and alternatives) corresponding to each concept term, to assist with search and display.

  • A java-based Cyc Inference Engine and the Cyc Knowledge Base Browser

  • Documentation and self-paced learning materials to help users achieve a basic- to intermediate-level understanding of the issues of knowledge representation and application development using Cyc.

  • A specification of CycL, the language in which Cyc (and hence OpenCyc) is written.

  • A specification of the Cyc API for application development.


OpenCyc is available for download from SourceForge under an OpenCyc License.

The OpenCyc KB content is also available via downloadable OWL files, as semantic web endpoints, and via web services.

Cycorp also offers a complete version of Cyc, including many more assertions and additional NL capabilities, under a ResearchCyc license at no cost for research purposes. For commercial applications, EnterpriseCyc provides a supported version of the knowledge base and reasoning technology that includes enterprise-grade development, deployment, and administration capabilities.

You can download the OpenCyc knowledgebase and inference system from SourceForge.

OpenCyc Ontologies (OWL Files)

The full OpenCyc content is available for download in the following OWL files:

md5 checksum: 96110c055c66b8774529b3b529ac2b55

Archived Versions

  • 2012 May 10

Permanent IDs: opencyc-2012-05-10.owl.gz

md5 checksum: b9d27434a4f1333980a60d31d989b467

Human-readable IDs: opencyc-2012-05-10-readable.owl.gz

md5 checksum: 30b9c78d069cce2148c3a735fba3e77e

  • 2010 August 15

Permanent IDs: opencyc-2010-08-15.owl.gz

md5 checksum: da28191aeb1885e243cb47d625e69d36

Human-readable IDs: opencyc-2010-08-15-readable.owl.gz

md5 checksum: 209d16a2858cdcded23ffd3c9f9e54a8

  • 2009 April 07

Permanent IDs: opencyc-2009-04-07.owl.gz

md5 checksum: 5fb3a25fb97d24312974bcf29675fae7

Human-readable IDs: opencyc-2009-04-07-readable.owl.gz

md5 checksum: 7ff7874b550dbdb27811ed50f240dcc4

  • 2008 June 10

Permanent IDs: opencyc-2008-06-10.owl.gz

md5 checksum: 5bc2cb422e9c4528392019387dcd27e2


All the texts above were extracted from pages from Copyright ©2018 Cycorp, Inc. All Rights Reserved.

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