Kelu vs OpenAI Responses API
Last reviewed:
OpenAI shut down the Assistants API on August 26, 2026. Its replacement is the Responses API, with the Conversations API for threads and a hosted file search tool over vector stores. It is a set of building blocks for your own assistant. Kelu is a packaged knowledge assistant: connectors, retrieval, the widget, bots and analytics are shipped, not built. This comparison is about product vs building blocks, and what each costs to run.
Choose the Responses API if the assistant is your product, or you need custom tools and flows, and you have engineers to build and run ingest, sync, UI, bots and analytics. Choose Kelu if you want a docs and support assistant that works now: 24 source types kept in sync, cited answers that abstain when your sources don't cover a question, and a widget, Slack and Teams bots, MCP and helpdesk surfaces included.
Feature comparison
Comparison based on OpenAI's own API docs, deprecation notices and pricing page. Time estimates for the build side are rough.
Where Kelu focuses differently
A product, not building blocks
The Responses API gives you a model, hosted file search and a chat UI kit. Turning them into a production assistant means building the ingest pipeline, the sync, the widget backend, the Slack and Teams bots, the analytics and the ops. Kelu ships all of that. The build-vs-buy question isn't 'can we build this?' — it's 'is this worth months of engineering, and an owner for years?'
Retrieval tuned for docs, out of the box
File search now does hybrid search with a ranker, which is a good base. What it doesn't do is prepare your docs: HTML→markdown that strips nav and boilerplate, code-block handling, chunks that follow headings rather than token counts, PDF structure, and a coverage check that decides whether to answer at all. Those are the pieces most build-your-own projects find they need after launch.
The connectors are the moat
Building one connector (say, Zendesk) with correct pagination, incremental sync and removal handling is weeks of engineering — a rough estimate. Doing 24 of them, and keeping each working as vendor APIs change, is a standing job. Kelu ships and maintains them, skips unchanged pages, and holds back large removals for review.
Keep your model and your bill
Bring your own model key (on every plan) means Kelu calls OpenAI, Anthropic, Google Gemini or AWS Bedrock on your account. You keep control over the model and the invoice; you skip owning the platform.
Got questions?
Frequently asked questions
Is the OpenAI Assistants API still available?
No. OpenAI announced its deprecation in August 2025 and removed it on August 26, 2026. The recommended replacement is the Responses API with the Conversations API; file search and vector stores carry over. Kelu was never built on the Assistants API, so the shutdown didn't affect it.
When would I still build on the Responses API instead?
If your assistant needs custom logic that isn't docs Q&A — a coding agent with your own tools, a multi-step workflow, an on-brand consumer character — the flexibility of building blocks is the right choice. For docs and support Q&A, a packaged product usually wins on time to value and ongoing upkeep.
Do I lose flexibility by using Kelu?
For custom agent flows, yes. For docs and support Q&A, much less — the hosted widget, a public REST and WebSocket API, and an MCP server give you enough surface to build your own experiences on top. React and JavaScript SDKs are on npm (@keluhq/sdk, @keluhq/react).
Can I bring my own OpenAI key?
Yes, on every plan. Bring your own model key sends answers through your own OpenAI, Anthropic, Google Gemini or AWS Bedrock account, under your agreement with that provider. You keep the model choice and the invoice; Kelu is the platform.
How does total cost compare?
Kelu is Free, Pro at $99 a month ($79 billed yearly), or custom Enterprise. Building on the Responses API means model and file search costs (with Kelu on your own key you pay the model costs too) plus engineering time — as a rough estimate, months for a production docs assistant with a widget and bots — plus ongoing upkeep as vendor APIs and models change.
See for yourself
Connect your docs and get your first AI-powered answer in under 5 minutes. No credit card required.
Free to start · No credit card required · Talk to Sales →