Fosnie vs Onyx, Open WebUI, and LibreChat

Onyx, Open WebUI, LibreChat, and Fosnie are all open-source, self-hosted AI workspaces you run on your own infrastructure. On the common ground - private chat, retrieval over your documents with citations, any-model/BYOK, agents, MCP, a code interpreter, voice, and single sign-on - they are broadly comparable in 2026. If you want a self-hosted ChatGPT for a team, any of them is a reasonable choice.

Fosnie is built for a narrower, harder job: regulated, document-heavy work where you must be able to review and edit generated documents, prove where every answer came from, and hand an auditor a tamper- evident record. That is the lens for this comparison. We have tried to be fair; where a competitor is stronger, we say so.

At a glance

How model routing differs

For this comparison, automatic prompt routing means choosing which configured LLM should answer a request using its requirements or a routing policy. Model selection, provider gateways and agent handoffs cover different parts of that job; the entries above describe the documented implementation, including the configuration or extensions it needs.

Fosnie includes automatic model routing in open-source Core and Enterprise. Auto supports Rules, Classifier and Hybrid strategies across local, cloud or mixed pools. A judge is optional for Rules and explicitly assigned for Classifier/Hybrid; it may run locally or in the cloud. The server checks model capabilities, reasoning effort, locality, permissions and shared usage limits before dispatch. Off, Shadow and Active support gradual rollout. Eligible failures can use one permitted alternate before output in supported callers; Manual stays pinned. The guide documents caller limits. Selection depends on configured profiles and evidence, with no guarantee of the best answer or savings.

Onyx documents visible models and default/fast model settings, plus integrations with LiteLLM Proxy and Bifrost. Routing can therefore be supplied by the configured gateway. Its Enterprise LLM Gateway also exposes approved models with access controls and usage limits, using an explicit provider/model ID. These guides do not establish a built-in prompt-complexity judge that automatically chooses the chat's main model.

Open WebUI explicitly documents routing through Pipe Functions, including choosing a cheaper or more expensive model from the prompt. Filter Functions can redirect requests based on content. This is a supported extension path, with installed or custom function code and its configuration determining the routing policy. A routing gateway can also sit behind its provider connection. It would be misleading to mark model routing as absent.

LibreChat lets each agent select its provider/model and supports model-driven handoffs to configured specialist agents. This can delegate work to an agent backed by a different model. It also documents LiteLLM and OpenRouter custom endpoints, where routing can be configured in the upstream service. Agent delegation and gateway routing are supported approaches; these pages do not establish a general chat Auto policy equivalent to Fosnie's Rules/Classifier/Hybrid settings.

The competitor notes are a review of the linked official documentation, not an exhaustive feature audit or a comparative routing benchmark. Evaluate the configured route on representative requests before making claims about accuracy, latency or cost.

Where each one is strongest

Onyx is the enterprise-search specialist: 50-plus prebuilt connectors and best-in-class retrieval over your existing tools. If your main need is "answer questions across SharePoint, Confluence, Slack and Drive," Onyx is the most complete out of the box.

Open WebUI has by far the largest community and ecosystem (140k+ stars), a very polished local-model experience, and a deep plugin/pipeline framework. It is the safe default for a self-hosted ChatGPT over Ollama. Note its licence changed in April 2025 to require retaining Open WebUI branding on deployments over 50 users; it is no longer OSI-approved.

LibreChat supports the widest range of model providers out of the box, with a strong multi-user chat UX, agents, artifacts, and a self-hostable code interpreter. If provider breadth and chat polish are your priority, it is excellent.

Fosnie is built for regulated, document-heavy teams: legal, audit, finance, and healthcare, who hold other people's confidential data. It is the only one of the four that combines first-class document generation with tracked-changes review, answer verification (groundedness), and a tamper-evident audit with legal holds and certified air-gap. If you have to defend an answer or a document to a regulator, that is the difference.

Fosnie vs Onyx

Onyx and Fosnie are the closest match: both do agentic RAG, deep research, a code interpreter, voice, and SSO/SCIM. Onyx wins on breadth of prebuilt connectors, so it is the better pick if your value is connecting to many SaaS sources. Fosnie wins where the work is producing and standing behind documents: it turns a generated DOCX into a tracked-changes review you accept or reject clause by clause, verifies answers against their sources and flags unsupported claims, and keeps a tamper-evident, hash-chained audit with legal holds and GDPR crypto-shred. Choose Onyx for enterprise search across your tools; choose Fosnie for document-heavy, auditable work under regulation.

Fosnie vs Open WebUI

Open WebUI is the most popular self-hosted AI UI and the most mature ecosystem. It is a great front-end for local models. Two things separate Fosnie: licensing and compliance. Fosnie is Apache-2.0 and imposes no branding restriction, whereas Open WebUI's licence requires keeping its branding on deployments over 50 users. And Fosnie is built as a compliance product: verification, tracked-changes documents, tamper-evident audit, legal holds, moderation, and certified air-gap, none of which are Open WebUI's focus. Choose Open WebUI for a polished local-LLM chat; choose Fosnie when the deployment has to pass a compliance review.

Fosnie vs LibreChat

LibreChat has the widest provider support and a polished multi-user chat experience, and its code interpreter can be self-hosted. Fosnie overlaps on chat, agents, MCP, and code execution, and pulls ahead on the document and compliance layer: first-class DOCX/PDF/XLSX generation with tracked-changes review and tabular review across many documents at once, groundedness verification, and a tamper-evident audit with legal holds and air-gap. Choose LibreChat for broad model access and general chat; choose Fosnie for regulated document work you have to be able to prove.

Sources

The routing section links directly to the official guides supporting each entry.

• Onyx: github.com/onyx-dot-app/onyx, onyx.app, changelog
• Open WebUI: docs.openwebui.com/features, licence, enterprise/security
• LibreChat: github.com/danny-avila/LibreChat, code interpreter, speech settings