LM Studio vs Open WebUI

LM Studio

OpenAI-compatible chat completions, responses, completions and embeddings, Anthropic-compatible /v1/messages and a native /api/v1, all on one port. Authentication is off by default, so any local process can call the server.

Open WebUI

Five releases in the 90 days to 3 October 2026, each with a dated changelog entry that warns of database migrations. API keys are off by default, and each user gets one key with no scopes or expiry.

LM Studio

1. Send Authorization: Bearer $LM_API_TOKEN when the owner gives you a token. With Require Authentication on, every request needs it
2. Pass previous_response_id to /api/v1/chat instead of resending the history, and store: false for one-off calls
3. List models with GET /api/v1/models before naming one. A named model that's downloaded loads just in time
4. Install the Python SDK pre-release (1.6.0b1) and pass api_token directly. It reads LMSTUDIO_API_TOKEN, not the LM_API_TOKEN the docs name
5. Set allowed_tools on every MCP integration. Without it the model sees every tool on the server

Open WebUI

1. Ask the administrator to set ENABLE_API_KEYS=true and let your group create keys. sk- keys are refused until then
2. Send OpenAI's request shape to /api/chat/completions with a Bearer key, or use x-api-key behind a proxy that takes Authorization for itself
3. Call /api/models first and use an id from it. Model IDs depend on the instance's connections
4. Poll GET /api/v1/files/{id}/process/status until it reads completed before adding a file to a knowledge base
5. Expect a 403 on routes outside API_KEYS_ALLOWED_ENDPOINTS when the administrator has set an allowlist