## Summary

The AI21 model list in LiteLLM is outdated. AI21 has retired all J2 models (`j2-light`, `j2-mid`, `j2-ultra`) and now only offers two models:

- `jamba-large-1.7-2025-07` (alias: `jamba-large-1.7`) - `jamba-mini-2-2026-01` (alias: `jamba-mini-2`)

Confirmed via the AI21 API:

```bash curl -s https://api.ai21.com/studio/v1/models \ -H "Authorization: Bearer $KEY" | python3 -m json.tool ```

Returns only those two models. Requests to `j2-ultra` etc. return `"The provided model is not supported"`.

## Additional issue

When adding AI21 models via the LiteLLM Admin UI, selecting an existing AI21 credential (that works for one model) does not seem to apply correctly to a second model added afterwards. The second model ends up with a wrong API key, even though the same credential was selected. After a proxy restart, the first model works fine but the second one fails with `AuthenticationError`. This might be a UI/credential-binding bug.

## Suggested fix

1. Update the AI21 model list to reflect the current two available models 2. Remove the deprecated J2 models from the default model definitions 3. Investigate credential binding when reusing existing AI21 credentials for m…