OpenBook vs Vellum
Vellum is a closed-source SaaS focused on the LLM development lifecycle: prompt engineering, evaluation, experimentation, and deploying workflows, with strong tooling for testing and comparing prompts. OpenBook is an open-source, self-hostable agentic platform — agents with long-term memory, an AI builder, a real workflow engine, and human-in-the-loop. They overlap on workflows but differ on focus and licensing.
At a glance
OpenBook and Vellum, capability by capability.
| Capability | OpenBook | Vellum |
|---|---|---|
| Open source | ||
| Self-hostable | ||
| Visual workflow builder | ||
| AI builds the workflow for you | ||
| First-class agents with memory | Partial | |
| Human-in-the-loop pause/resume | Partial | |
| Prompt evaluation & experimentation tooling | Basic | |
| Bring your own model keys | ||
| No closed-SaaS subscription required |
Why teams pick OpenBook over Vellum
Open source & self-hosted
Run OpenBook on your infrastructure with your keys and read every line. Vellum is a closed SaaS.
Agentic runtime with memory
OpenBook agents run a plan-act-observe loop and remember across runs by default. Vellum centers on prompts, evaluation, and workflow deployment.
AI builder + human-in-the-loop
Describe a workflow and OpenBook wires the graph, with branching, error paths, and pause-for-approval that resumes from an inbox.
No per-seat or per-run lock-in
Self-host and pay your model provider directly instead of a closed SaaS subscription with usage limits.
MIT, self-host, your keys.
Closed SaaS with subscription pricing.
When to choose which
- You want a self-hostable agentic platform with agents, memory, and human-in-the-loop
- You want an AI builder and a real workflow engine without a closed-SaaS subscription
- You want to own your data, prompts, and infrastructure
- Your priority is rigorous prompt engineering, evaluation, and experiment tracking
- You want a managed LLMOps SaaS with mature testing and comparison tooling
Recreate Vellum workflows as OpenBook graphs and prompts as agent system prompts. Keep using Vellum-style evaluations during development, then deploy the workflow on self-hosted OpenBook.
Frequently asked questions
Build your first agentic workflow today.
OpenBook is free and open source. Self-host it in minutes, or read the docs to see how far the engine goes.