Use Modellix LLM with Reasonix

Configure Reasonix to call the Modellix LLM gateway. Reasonix is a local coding agent (CLI/TUI, desktop app, browser UI, or ACP). It has no built-in Modellix provider, so add an OpenAI-compatible [[providers]] entry in ~/.reasonix/config.toml that points at Chat Completions on POST /v1/chat/completions.

This page covers LLM text only (https://llm.modellix.ai).Modellix model IDs are provider/name (for example openai/gpt-5.5). Put that full string in model or models so Reasonix sends it unchanged in the request body. See Models & Pricing.

Set Up Reasonix

Install Reasonix

Install the 1.x CLI (npm is the documented default):

npm i -g reasonix

brew install esengine/reasonix/reasonix

Desktop downloads are on the Reasonix docs. CLI and desktop share the same config and credential files.

Store the Modellix API Key

Create a key in the Modellix console. Reasonix reads provider secrets from its global .env, not from your shell profile or a project .env.macOS / Linux: ~/.reasonix/.env
Windows: %APPDATA%\reasonix\.env

MODELLIX_API_KEY=mdlx-xxxxxxxx

Replace mdlx-xxxxxxxx with your Modellix API key. You can also paste the key in reasonix setup or desktop Settings → Model → Access; those flows write the same file.

Use a Modellix API key, not a DeepSeek, OpenAI, or other vendor platform key. Shell export MODELLIX_API_KEY=... is not a Reasonix provider-key fallback.

Add a Custom Provider

Edit the user config at ~/.reasonix/config.toml (Windows: %APPDATA%\reasonix\config.toml). Merge the [[providers]] table into an existing file; do not delete other providers.

default_model = "modellix"

[[providers]]
name = "modellix"
kind = "openai"
base_url = "https://llm.modellix.ai/v1"
models = [
  "openai/gpt-5.5",
  "openai/gpt-5.6-sol",
  "anthropic/claude-sonnet-5",
  "google/gemini-3.6-flash",
  "xai/grok-4.6",
]
default = "openai/gpt-5.5"
api_key_env = "MODELLIX_API_KEY"
context_window = 200000

Add or remove IDs in models as needed. Full catalog: Models & Pricing.

Field	Value
`name`	Local provider ID (use `modellix`; do not reuse `openai` or `anthropic`)
`kind`	`openai` for Chat Completions
`base_url`	`https://llm.modellix.ai/v1` (Reasonix posts to `{base_url}/chat/completions`)
`models`	Exact Modellix Model IDs (`provider/name`)
`default`	Default Modellix ID for this provider
`api_key_env`	`MODELLIX_API_KEY` (must match a key in `~/.reasonix/.env`)
`context_window`	Token window used for compaction; raise it if the catalog model is larger
`default_model`	Reasonix picker ref: provider name (`modellix`) or `modellix/<model-id>`

Config resolution is flags → ./reasonix.toml → user config.toml. Keep personal API providers in the user file.

You do not need a separate Anthropic kind or base URL. Register anthropic/... and google/... IDs on the same Modellix kind = "openai" entry; traffic goes through OpenAI-compatible Chat Completions. Native Anthropic Messages is for the Anthropic SDK and Claude Code.

In Reasonix 1.24+, the desktop custom-provider form stores an exact API address as request_url (no path rewriting). If you use that form, enter https://llm.modellix.ai/v1/chat/completions. Manual base_url = "https://llm.modellix.ai/v1" remains valid for TOML edits.

Start a Session

From your project directory:

cd your-project
reasonix

Switch models with /model. Prefer the explicit Reasonix ref modellix/openai/gpt-5.5 (provider name, then the Modellix ID). Headless:

reasonix run --model "modellix/openai/gpt-5.5" "Explain this repo"

reasonix setup can also add a custom OpenAI-compatible provider and write the key; afterwards, confirm base_url / request_url and models match the table above.

Troubleshooting

Symptom	Check
401 / missing API key	`MODELLIX_API_KEY` is in `~/.reasonix/.env` (or `%APPDATA%\reasonix\.env`), and `api_key_env` matches that name
Model not found / unknown model	`models` lists the full ID (`openai/gpt-5.5`); select `modellix/openai/gpt-5.5` or the provider name `modellix`
Wrong path / URL errors	`base_url` is `https://llm.modellix.ai/v1`, or `request_url` is `https://llm.modellix.ai/v1/chat/completions` — not the media API host (`https://api.modellix.ai`)
Traffic hits DeepSeek or another vendor	You selected the `modellix` provider, not a built-in DeepSeek / OpenAI / Anthropic preset
Early compaction	Raise `context_window` for the catalog model; custom providers no longer inherit DeepSeek window defaults
Provider name clash	Do not name the Reasonix provider `openai` or `anthropic` — Modellix IDs already start with those prefixes

Reasonix docs — install, config paths, TUI and desktop
Models & Pricing — Model IDs and rates
LLM API guide — protocols and curl examples
OpenAI SDK — same /v1 Chat Completions gateway
OpenCode · Grok Build — other OpenAI-compatible agent setups

Get Started

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Use Modellix LLM with Reasonix

Set Up Reasonix

Troubleshooting

​Set Up Reasonix

​Troubleshooting

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Set Up Reasonix

Troubleshooting

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