Jan vs llama.cpp

Jan

Apache-2.0, with installers for macOS, Windows and Linux plus Flathub and the Microsoft Store. No release since 0.8.4 on 23 July 2026, while a security fix waits on main.

llama.cpp

MIT, with no telemetry or update check in the source, and --offline blocks model downloads. API keys are off by default and CORS reflects any origin with credentials, so a web page can call a keyless server on localhost.

Jan

1. Ask the owner to start the server (Settings, Local API Server) or run jan serve. Nothing listens until then
2. Call http://127.0.0.1:1337/v1 for the app and localhost:6767/v1 for jan serve. The ports differ
3. Read /openapi.json from the running server, not the spec on the docs site, which describes the retired Cortex API
4. Branch on the status code. Error bodies are plain text
5. Keep the bind at 127.0.0.1 on 0.8.4. Trusted Hosts is ignored on 0.0.0.0 until the next release

llama.cpp

1. Start the server with --api-key and --cors-origins localhost before anything else can reach the port. Both are off by default
2. Pass n_predict or max_tokens. Generation is unbounded by default
3. Send response_fields to /completion to drop the fields you don't read
4. Wait and retry on a 503 unavailable_error. The model is still loading
5. Read the server README of the build you run. Behaviour changes between nightly builds without a changelog entry