OpenCode

1. Overview

OpenCode is an open-source AI coding assistant with first-class support for 75+ models and self-hosted deployments. Through GravitexAI, you can use mainstream models (GPT, Claude, Gemini, Qwen…) inside OpenCode without configuring every vendor separately.

Unified multi-model

One provider, full GPT / Claude / Gemini / Qwen family

Self-host friendly

Supports your own backends and per-project config overrides

Responses API ready

apiCompatibility: "responses" works with the GPT Codex series

Open & auditable

Fully open-source, customize as needed

Download: https://opencode.ai/

2. Quick Setup (GravitexAI)

2.1 Get an API key

Go to the GravitexAI console and register or log in.

Create a token

Open API Keys, click “Create new token”, and copy the sk-xxxxxxxxxx key.

2.2 Configure a custom provider in OpenCode

Open provider settings

In OpenCode, go to Server / Provider settings and select Add custom provider (OpenAI-compatible).

Fill in provider info

Field	Value
Provider ID	`gravitex` (lowercase, digits, hyphens or underscores)
Display name	`GravitexAI`
Base URL	`https://api.gravitex.ai/v1` (must end with `/v1`)
API key	Paste your GravitexAI key from the previous step

Add models

Under Models, add model IDs you want to use (e.g. gpt-5.5, claude-sonnet-4-6, gemini-3.5-flash). IDs must match the GravitexAI model list.

Save and use

After saving, select via providerID/modelID in chats and settings, e.g. gravitex/gpt-5.5.

2.3 Switching models

In chat or settings, pick the configured provider/model (e.g. gravitex/gpt-5.5) to switch.

For self-hosted or backup GravitexAI endpoints, change the Base URL, e.g. http://your-server:3003/v1.
Set a default model in project or global opencode.json via "model": "gravitex/modelID".

3. Some Models Require the Responses API (Important)

Some Azure / OpenAI models only support the Responses API, not the legacy Chat Completions endpoint. When OpenCode defaults to Chat Completions you’ll see:

The chatCompletion operation does not work with the specified model, gpt-5.1-codex. Please choose different model and try again.

The screenshot below shows how this error appears in OpenCode:

Error when using gpt-5.1-codex with Chat Completions

3.1 Models that require Responses API

Model ID / family	Notes
gpt-5.1-codex	GPT 5.1 Codex (code-focused) — Responses API only
gpt-5.2-codex	Same as above
computer-use-preview	Experimental model used with the Responses API computer-use tools

For the latest full list, see Azure / vendor docs:

3.2 How to configure in OpenCode

Add the apiCompatibility parameter to a model in your config — no code changes needed.

Locate the config file

Windows: C:\Users\<username>\.config\opencode\opencode.jsonc
macOS / Linux: ~/.config/opencode/opencode.jsonc

Responses API requirement for some models

Add the parameter

In your existing custom provider (pointing at GravitexAI or your own API), add "apiCompatibility": "responses" for models that need it (e.g. gpt-5.1-codex):

opencode.jsonc: apiCompatibility responses for gpt-5.1-codex

{
  "$schema": "https://opencode.ai/config.json",
  "disabled_providers": [
    "backup_gravitex"
  ],
  "provider": {
    "backup_gravitex": {
      "name": "backup_gravitex",
      "npm": "@ai-sdk/openai-compatible",
      "models": {
        "gpt-5.2": {
          "name": "gpt-5.2"
        },
        "gpt-5.1-codex": {
          "name": "gpt-5.1-codex",
          "apiCompatibility": "responses"
        },
        "gpt-5.1-chat": {
          "name": "gpt-5.1-chat"
        }
      },
      "options": {
        "baseURL": "xxxxxxxx"
      }
    },
    "backup_v1": {
      "name": "backup_v1",
      "npm": "@ai-sdk/openai-compatible",
      "models": {
        "gpt-5.2": {
          "name": "gpt-5.2"
        },
        "gpt-5.1-codex": {
          "name": "gpt-5.1-codex",
          "apiCompatibility": "responses"
        },
        "gpt-5.1-chat": {
          "name": "gpt-5.1-chat"
        }
      },
      "options": {
        "baseURL": "https://api.gravitex.ai/v1"
      }
    }
  }
}

After saving, selecting that provider’s gpt-5.1-codex (e.g. backup_v1/gpt-5.1-codex) will send requests to that baseURL using the Responses API format.

Verify the setup

Pick a correctly configured model (e.g. backup_v1/gpt-5.1-chat) and test a chat — successful reply means you’re good:

3.3 Summary

Scenario	What to do
Models that only support Responses (e.g. gpt-5.1-codex, gpt-5.2-codex)	Add `"apiCompatibility": "responses"` to that model under your custom provider’s models in `opencode.jsonc`
Regular models (e.g. gpt-5.5, claude-sonnet-4-6, gemini-3.5-flash)	No `apiCompatibility` needed — follow Quick Setup

4. Recommended Models (via GravitexAI)

Category	Model ID examples	Notes
Flagship coding	`gpt-5.5`, `claude-opus-4-7`	Best overall coding ability
Codex series	`gpt-5.1-codex`	Requires Responses API (see Section 3)
General chat + code	`gpt-5.4`, `claude-sonnet-4-6`, `claude-sonnet-4-5-20250929`	Works out of the box
Fast / low latency	`gemini-3.5-flash`, `claude-haiku-4-5-20251001`	Great for completions & tool use
Cost-effective	`gpt-5.4-mini`, `gemini-3.1-flash-lite-preview`, `qwen3-coder-plus`	High concurrency / batch

See the GravitexAI model list for complete IDs.

Success example

A normal chat in OpenCode using GravitexAI:

5. FAQ

`The chatCompletion operation does not work…` error

That model only supports the Responses API. Add "apiCompatibility": "responses" to it in opencode.jsonc — see Section 3.

401 / invalid API key

Check the key for completeness and trailing whitespace.
Confirm it isn’t deleted/disabled in the GravitexAI console.
Ensure your balance is positive.

404 / endpoint not found

Make sure the Base URL ends with /v1: https://api.gravitex.ai/v1.

`model not found` for a valid-looking ID

Model IDs must exactly match the GravitexAI list. Watch the case and version suffix (e.g. claude-sonnet-4-5-20250929, not claude-sonnet-4-5).

How to standardize across a team?

Commit opencode.jsonc to .config/opencode/ in the repo (or the project root). Each engineer brings their own API key.

6. References

OpenCode site and download: https://opencode.ai/
OpenCode config and models: Models, Providers
GravitexAI console: https://maas.gravitex.ai
Model catalog: https://maas.gravitex.ai/#/models

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1. Overview

Unified multi-model

Self-host friendly

Responses API ready

Open & auditable