# MODEL_NOT_FOUND
## Checklist
1. Spell-check the model identifier character by character. `gpt-5.5` vs `gpt-5-5`, `claude-sonnet-4-6` vs a made-up variant. Copy the string from the docs, do not type it from memory.
2. If you use `init_chat_model`, try the explicit `provider:model` form (`"openai:gpt-5.5"`) so there is no ambiguity about which provider should resolve the name.
3. Behind a proxy, gateway, or model wrapper? Confirm the permitted model names on that layer. Proxies often restrict or rename models, and the error then comes from the proxy, not the provider.
4. Brand-new model names need a recent provider package. An old langchain-openai may not know a model released last month.
## Rule
In JS this is the MODEL_NOT_FOUND error code. When the name looks right, the proxy is the next suspect, not the SDK.