Fantasy – Build AI agents with Go. Multi-provider, multi-model, one API

4 hours ago 2

Build AI agents with Go. Multi-provider, multi-model, one API.

Choose a model and provider
Add some tools
Compile to native machine code and let it rip

Note

Fantasy is currently a preview. Expect API changes.

import "charm.land/fantasy" import "charm.land/fantasy/providers/openrouter" // Choose your fave provider. provider, err := openrouter.New(openrouter.WithAPIKey(myHotKey)) if err != nil { fmt.Fprintln(os.Stderr, "Whoops:", err) os.Exit(1) } ctx := context.Background() // Pick your fave model. model, err := provider.LanguageModel(ctx, "moonshotai/kimi-k2") if err != nil { fmt.Fprintln(os.Stderr, "Dang:", err) os.Exit(1) } // Make your own tools. cuteDogTool := fantasy.NewAgentTool( "cute_dog_tool", "Provide up-to-date info on cute dogs.", fetchCuteDogInfoFunc, ) // Equip your agent. agent := fantasy.NewAgent( model, fantasy.WithSystemPrompt("You are a moderately helpful, dog-centric assistant."), fantasy.WithTools(cuteDogTool), ) // Put that agent to work! const prompt = "Find all the cute dogs in Silver Lake, Los Angeles." result, err := agent.Generate(ctx, fantasy.AgentCall{Prompt: prompt}) if err != nil { fmt.Fprintln(os.Stderr, "Oof:", err) os.Exit(1) } fmt.Println(result.Response.Content.Text())

🍔 For the full implementation and more see the examples directory.

Multi-model? Multi-provider?

Yeah! Fantasy is designed to support a wide variety of providers and models under a single API. While many providers such as Microsoft Azure, Amazon Bedrock, and OpenRouter have dedicated packages in Fantasy, many others work just fine with openaicompat, the generic OpenAI-compatible layer. That said, if you find a provider that’s not compatible and needs special treatment, please let us know in an issue (or open a PR).

We built Fantasy to power Crush, a hot coding agent for glamourously invincible development. Given that, Fantasy does not yet support things like: