What is a Chat Completions API (OpenAI-compatible)?

What a request looks like

The request goes to the base URL plus /chat/completions, with your key in an Authorization: Bearer header. The body is JSON:

{ "model": "gemma-4-12b", "messages": [ { "role": "system", "content": "You are Captain Mireya Black, a pirate captain..." }, { "role": "user", "content": "*I tug at the ropes.* You'll regret this." } ], "max_tokens": 500, "temperature": 0.9, "stream": true }

The reply comes back with the new message under choices[0].message.content. With stream set to true it arrives piece by piece, so apps can show the text as it is written.

Why "compatible" matters

Because so many providers accept the same shape, an app only needs to support it once. That is why SillyTavern has a Custom (OpenAI-compatible) source and JanitorAI has proxy settings: point them at any compatible URL and they work. For you, it means one account and one key can serve several apps.

The API has no memory of its own. Every request carries the whole conversation the model should see, and the app decides what goes in: the character card as a system message, the history as user and assistant messages, and sampler settings like temperature and min_p.

Common mistakes

• Mixing up the base URL and the full endpoint. SillyTavern wants the base (ending in /v1); JanitorAI wants the full URL ending in /chat/completions.
• Putting the key in a public website or app bundle. Keep it on a server.
• Assuming every compatible API supports every feature. Images, tools and embeddings are separate from text chat.
• Retrying failed requests instantly in a loop. On a 429, wait and back off.

The UnsavedAI API

Make a key at /setup and use the models gemma-4-12b (all plans) or gemma-4-31b (Priority), with about 61,000 tokens of context. Supported settings include temperature, top_p, top_k, min_p, repetition_penalty, presence and frequency penalties, seed and stop; unknown fields are ignored, so existing presets work. Free writes one reply at a time and Priority two. API traffic is never stored. Step-by-step guides: SillyTavern, JanitorAI and building your own app. If you just want to chat, Captain Mireya Black and every other house character work right in the browser.

Questions people ask