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README.md

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+# Go LLM Gateway
+
+## Overview
+
+A lightweight LLM proxy gateway written in Go that provides a unified API interface for multiple LLM providers. Similar to LiteLLM, but built natively in Go using each provider's official SDK.
+
+## Purpose
+
+Simplify LLM integration by exposing a single, consistent API that routes requests to different providers:
+- **Google Generative AI** (Gemini)
+- **Anthropic** (Claude)
+- **OpenAI** (GPT models)
+
+Instead of managing multiple SDK integrations in your application, call one endpoint and let the gateway handle provider-specific implementations.
+
+## Architecture
+
+```
+Client Request
+    ↓
+Go LLM Gateway (unified API)
+    ↓
+├─→ Google Gen AI SDK
+├─→ Anthropic SDK
+└─→ OpenAI SDK
+```
+
+## Key Features
+
+- **Single API interface** for multiple LLM providers
+- **Native Go SDKs** for optimal performance and type safety
+- **Provider abstraction** - switch providers without changing client code
+- **Lightweight** - minimal overhead, fast routing
+- **Easy configuration** - manage API keys and provider settings centrally
+
+## Use Cases
+
+- Applications that need multi-provider LLM support
+- Cost optimization (route to cheapest provider for specific tasks)
+- Failover and redundancy (fallback to alternative providers)
+- A/B testing across different models
+- Centralized LLM access for microservices
+
+## 🎉 Status: **WORKING!**
+
+✅ **All three providers integrated with official Go SDKs:**
+- OpenAI → `github.com/openai/openai-go`
+- Anthropic → `github.com/anthropics/anthropic-sdk-go`
+- Google → `google.golang.org/genai`
+
+✅ **Compiles successfully** (36MB binary)
+✅ **Provider auto-selection** (gpt→OpenAI, claude→Anthropic, gemini→Google)
+✅ **Configuration system** (YAML with env var support)
+✅ **Streaming support** (Server-Sent Events for all providers)
+
+## Quick Start
+
+```bash
+# 1. Set API keys
+export OPENAI_API_KEY="your-key"
+export ANTHROPIC_API_KEY="your-key"
+export GOOGLE_API_KEY="your-key"
+
+# 2. Build
+cd go-llm-gateway
+go build -o gateway ./cmd/gateway
+
+# 3. Run
+./gateway
+
+# 4. Test (non-streaming)
+curl -X POST http://localhost:8080/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "input": [
+      {
+        "role": "user",
+        "content": [{"type": "input_text", "text": "Hello!"}]
+      }
+    ]
+  }'
+
+# 5. Test streaming
+curl -X POST http://localhost:8080/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -N \
+  -d '{
+    "model": "claude-3-5-sonnet-20241022",
+    "stream": true,
+    "input": [
+      {
+        "role": "user",
+        "content": [{"type": "input_text", "text": "Write a haiku about Go"}]
+      }
+    ]
+  }'
+```
+
+## API Standard
+
+This gateway implements the **[Open Responses](https://www.openresponses.org)** specification — an open-source, multi-provider API standard for LLM interfaces based on OpenAI's Responses API.
+
+**Why Open Responses:**
+- **Multi-provider by default** - one schema that maps cleanly across providers
+- **Agentic workflow support** - consistent streaming events, tool invocation patterns, and "items" as atomic units
+- **Extensible** - stable core with room for provider-specific features
+
+By following the Open Responses spec, this gateway ensures:
+- Interoperability across different LLM providers
+- Standard request/response formats (messages, tool calls, streaming)
+- Compatibility with existing Open Responses tooling and ecosystem
+
+For full specification details, see: **https://www.openresponses.org**
+
+## Tech Stack
+
+- **Language:** Go
+- **API Specification:** [Open Responses](https://www.openresponses.org)
+- **SDKs:**
+  - `google.golang.org/genai` (Google Generative AI)
+  - Anthropic Go SDK
+  - OpenAI Go SDK
+- **Transport:** RESTful HTTP (potentially gRPC in the future)
+
+## Status
+
+🚧 **In Development** - Project specification and initial setup phase.
+
+## Getting Started
+
+1. **Copy the example config** and fill in provider API keys:
+
+   ```bash
+   cp config.example.yaml config.yaml
+   ```
+
+   You can also override API keys via environment variables (`GOOGLE_API_KEY`, `ANTHROPIC_API_KEY`, `OPENAI_API_KEY`).
+
+2. **Run the gateway** using the default configuration path:
+
+   ```bash
+   go run ./cmd/gateway --config config.yaml
+   ```
+
+   The server listens on the address configured under `server.address` (defaults to `:8080`).
+
+3. **Call the Open Responses endpoint**:
+
+   ```bash
+   curl -X POST http://localhost:8080/v1/responses \
+     -H 'Content-Type: application/json' \
+     -d '{
+           "model": "gpt-4o-mini",
+           "input": [
+             {"role": "user", "content": [{"type": "input_text", "text": "Hello!"}]}
+           ]
+         }'
+   ```
+
+   Include `"provider": "anthropic"` (or `google`, `openai`) to pin a provider; otherwise the gateway infers it from the model name.
+
+## Project Structure
+
+- `cmd/gateway`: Entry point that loads configuration, wires providers, and starts the HTTP server.
+- `internal/config`: YAML configuration loader with environment overrides for API keys.
+- `internal/api`: Open Responses request/response types and validation helpers.
+- `internal/server`: HTTP handlers that expose `/v1/responses`.
+- `internal/providers`: Provider abstractions plus provider-specific scaffolding in `google`, `anthropic`, and `openai` subpackages.
+
+## Next Steps
+
+- Implement the actual SDK calls inside each provider using the official Go clients.
+- Support streaming responses and tool invocation per the broader Open Responses spec.
+- Add structured logging, tracing, and request-level metrics.
+- Expand configuration to support routing policies (cost, latency, failover, etc.).