App config & language

Pass your app’s model choice, instructions, agent definitions, and tool declarations in config when you call Croche.open(...). Tool handlers and credentials stay outside that config.

Choose a model

Your app can choose the model. Set model inside the config passed to Croche.open, not as a top-level open option:

const config = {
  model: 'deepseek/deepseek-v4.1-flash',
  instructions: 'You are a friendly guide. Keep replies brief.',
};
// Use this as the config option in your existing Croche.open call.

Scope	Config field
Project	config.model
Project language	config.languages.<tag>.model
Agent	config.agents.<agentId>.model
Agent language	config.agents.<agentId>.languages.<tag>.model

For the selected agent and language, later applicable levels override earlier ones in that order: project → project language → agent → agent language. Omitting model at one level inherits the preceding applicable value. Modes do not declare model.

If no applicable level sets model, the default is deepseek/deepseek-v4.1-flash, with openai/gpt-6-luna fallback only at reasoning default or off, not low, medium, or high. See Models for recommendations, fallback limits, and the allowed model IDs. Set config.model explicitly when you want a particular model.

User language and config language are different

Option	Meaning
language on Croche.open(...)	The user’s language, as a BCP-47 tag such as ko or en-US
config.defaultLanguage	The language the base config is written in, default "en"; not the user’s language or a fallback for it
config.languages.<tag>	A translated config branch for that language tag

language selects the matching translated branch in config.languages.<tag>: the exact tag first, then the primary subtag. For ko-KR, Croche looks for ko-KR, then ko. If neither matches, the base config is used as is, in the language recorded by config.defaultLanguage. config.defaultLanguage is used only to select the config layer; it does not change the user’s language. Croche does not translate the base config for you.

An English-only config still serves a Korean user. For example, with config.defaultLanguage: 'en', no matching Korean branch, and language: 'ko', the app uses the unchanged English base config. A Korean user’s language does not have to match the language in which you wrote your config.

When you omit language

The default contract, when your app does not pass language, is the device or browser locale on every SDK. Availability differs by SDK:

SDK environment	Locale source
Browser	navigator.language
React Native	Automatic device locale pending 0.5.1; pass language explicitly until verified
Native Swift	Automatic device locale pending 0.5.1; final native API review pending
Native Kotlin	Automatic device locale pending 0.5.1; final native API review pending

For a Node backend serving multiple people, pass each user’s language explicitly rather than treating the server’s locale as the user’s. With mobile 0.5.0 examples, pass language explicitly; automatic mobile device-locale selection is not yet verified.

The reply language

The model is not told the value of language. It replies in the language the user writes, unless your instructions say otherwise. The option selects config; it is not a command to make the model reply in that language.

In the English-config/Korean-user example, a user can write in Korean and receive a Korean reply without a Korean config branch, unless the instructions require another reply language.

Studio config replaces code config

A Studio AI config received through Croche.open(...) replaces the app’s code config as a whole, for both drafts and releases. It does not merge with the code config.

Use Croche.open(...) in TypeScript or React Native for the hackathon. Native Swift and Kotlin setup is pending API review. The separate CrocheRuntime.create(...) API never uses Studio config.

Changes apply on the next open

A Studio config takes effect on the next open after a sync, never in an already-open session. Saving a draft or publishing a release does not immediately change a running session.

Drafts reach only installations using a debug key (debugKey). Every debug key follows drafts by default; there is no toggle. Your development run can therefore use the Studio draft instead of the code config.

Include all your tools

A config declaring a tool your app has not registered is not delivered. Register handlers in app code and enforce permissions there.

A draft must include every tool your app uses. If you leave a tool out, the agent loses access to it on the next open after a sync, even if its handler remains registered. Omitted tools are not added back from the code config.

Keep keys and user secrets out of your config. See AI config & Test for the Studio steps.