OpenCode Engine

The OpenCode engine invokes the opencode CLI, which supports multiple LLM providers.

Prerequisites

• Install OpenCode: opencode available on PATH
• Set the API key for your chosen provider (see below)

Configuration

# golem.yaml
name: my-bot
engine: opencode
model: anthropic/claude-sonnet-4-5   # optional, format: provider/model

Choosing a Model

OpenCode uses a provider/model format. The provider prefix also determines which API key environment variable is used.

List available models:

opencode models

OpenCode supports 75+ providers via the AI SDK. The canonical source for all valid model strings is models.dev.

Common examples:

Model string	Provider	API key env var
anthropic/claude-sonnet-4-5-20250929	Anthropic	ANTHROPIC_API_KEY
anthropic/claude-opus-4-5	Anthropic	ANTHROPIC_API_KEY
openai/gpt-5	OpenAI	OPENAI_API_KEY
openai/gpt-4o	OpenAI	OPENAI_API_KEY
openrouter/anthropic/claude-opus-4-6	OpenRouter	OPENROUTER_API_KEY
google/gemini-2.5-flash	Google	GOOGLE_GENERATIVE_AI_API_KEY
deepseek/deepseek-chat	DeepSeek	DEEPSEEK_API_KEY
groq/llama-3.3-70b-versatile	Groq	GROQ_API_KEY

GolemBot automatically maps the provider prefix to the correct env var when apiKey is passed via createAssistant().

Override at runtime — pass model to createAssistant():

const bot = createAssistant({ dir: './my-bot', model: 'openai/gpt-4o' })

How It Works

CLI Invocation

opencode run "<prompt>" \
  --format json

Optional flags:

• --session <sessionId> — resume a previous session
• --model <provider/model> — specify model

Multi-Provider Support

OpenCode supports many LLM providers. GolemBot automatically resolves the correct API key environment variable based on the model prefix:

Model prefix	Environment variable
anthropic/	ANTHROPIC_API_KEY
openai/	OPENAI_API_KEY
openrouter/	OPENROUTER_API_KEY
groq/	GROQ_API_KEY
azure/	AZURE_API_KEY
(others)	Passed through as-is

If you pass apiKey via createAssistant(), GolemBot infers the correct env var name from the model prefix.

Skill Injection

Skills are symlinked into .opencode/skills/:

my-bot/
├── .opencode/
│   └── skills/
│       ├── general -> ../../skills/general
│       └── im-adapter -> ../../skills/im-adapter
├── opencode.json
└── skills/
    ├── general/
    └── im-adapter/

Additionally, GolemBot writes or updates opencode.json with permission and model configuration:

{
  "permission": { "*": "allow" },
  "model": "anthropic/claude-sonnet"
}

Output Parsing

OpenCode emits NDJSON (--format json). The parser handles:

• text events — streamed text content
• tool_use events — tool invocations
• step_finish events — accumulated per-step (not emitted individually); cost is summed
• error events — from both stdout and stderr

A single done event is emitted when the process closes, with accumulated cost.

Session Resume

Sessions use --session <ses_xxx> format. Like other engines, resume failures trigger an automatic fallback to a fresh session.

Notes

• OpenCode is the most flexible engine in terms of provider support
• The opencode.json permission config ("*": "allow") bypasses all permission prompts for automated operation
• Cost tracking aggregates across all steps in a conversation turn