Haystack is an open-source Python framework for building applications and agents on top of large language models. Developers assemble modular pipelines for retrieval, routing, memory and generation, and connect them to model providers and search or vector stores such as OpenAI, Anthropic, Hugging Face, Weaviate, Pinecone and Elasticsearch. Typical uses are retrieval-augmented generation, semantic search, question answering and multi-step agents. Haystack is installed as a library and runs wherever you run your own code; pipelines are serialisable and Kubernetes-ready.
Haystack is maintained by Berlin-based deepset GmbH, which also has an office in New York. The code is published under the Apache 2.0 licence on GitHub, so you can inspect, modify and self-host the framework without relying on a vendor-operated service. For commercial needs, deepset offers the Haystack Enterprise Platform, built on the open-source framework and available in the cloud or self-hosted. Where your data ends up depends on the models and stores you connect. A European organisation can therefore build a fully EU-based setup by choosing European infrastructure and providers.