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ARCHITECTURE.md
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# LiteLLM Architecture - LiteLLM SDK + AI Gateway
This document helps contributors understand where to make changes in the LiteLLM proxy.
This document helps contributors understand where to make changes in LiteLLM.
## 1. Request Flow
---
## 1. AI Gateway (Proxy) Request Flow
The AI Gateway (`litellm/proxy/`) wraps the SDK with authentication, rate limiting, and management features.
```mermaid
sequenceDiagram
@ -30,7 +34,7 @@ sequenceDiagram
Handler-->>Client: ModelResponse
```
### Proxy Server Components
### Proxy Components
```mermaid
graph TD
@ -65,7 +69,46 @@ graph TD
Main --> Client
```
### SDK Components (litellm/)
**Key proxy files:**
- `proxy/proxy_server.py` - Main API endpoints
- `proxy/auth/` - Authentication (API keys, JWT, OAuth2)
- `proxy/hooks/` - Proxy-level callbacks
- `router.py` - Load balancing, fallbacks
- `router_strategy/` - Routing algorithms (`lowest_latency.py`, `simple_shuffle.py`, etc.)
**LLM-specific proxy endpoints:**
| Endpoint | Directory | Purpose |
|----------|-----------|---------|
| `/v1/messages` | `proxy/anthropic_endpoints/` | Anthropic Messages API |
| `/vertex-ai/*` | `proxy/vertex_ai_endpoints/` | Vertex AI passthrough |
| `/gemini/*` | `proxy/google_endpoints/` | Google AI Studio passthrough |
| `/v1/images/*` | `proxy/image_endpoints/` | Image generation |
| `/v1/batches` | `proxy/batches_endpoints/` | Batch processing |
| `/v1/files` | `proxy/openai_files_endpoints/` | File uploads |
| `/v1/fine_tuning` | `proxy/fine_tuning_endpoints/` | Fine-tuning jobs |
| `/v1/rerank` | `proxy/rerank_endpoints/` | Reranking |
| `/v1/responses` | `proxy/response_api_endpoints/` | OpenAI Responses API |
| `/v1/vector_stores` | `proxy/vector_store_endpoints/` | Vector stores |
| `/*` (passthrough) | `proxy/pass_through_endpoints/` | Direct provider passthrough |
**Proxy Hooks** (`proxy/hooks/__init__.py`):
| Hook | File | Purpose |
|------|------|---------|
| `max_budget_limiter` | `proxy/hooks/max_budget_limiter.py` | Enforce budget limits |
| `parallel_request_limiter` | `proxy/hooks/parallel_request_limiter_v3.py` | Rate limiting per key/user |
| `cache_control_check` | `proxy/hooks/cache_control_check.py` | Cache validation |
| `responses_id_security` | `proxy/hooks/responses_id_security.py` | Response ID validation |
| `litellm_skills` | `proxy/hooks/skills_injection.py` | Skills injection |
To add a new proxy hook, implement `CustomLogger` and register in `PROXY_HOOKS`.
---
## 2. SDK Request Flow
The SDK (`litellm/`) provides the core LLM calling functionality used by both direct SDK users and the AI Gateway.
```mermaid
graph TD
@ -114,42 +157,18 @@ graph TD
Response -.->|async| Callbacks
```
**Key files:**
- `proxy/proxy_server.py` - Main API endpoints
- `proxy/auth/` - Authentication
- `proxy/hooks/` - Proxy-level callbacks (see table below)
- `router.py` - Load balancing, fallbacks
- `router_strategy/` - Routing algorithms (`lowest_latency.py`, `simple_shuffle.py`, etc.)
**Key SDK files:**
- `main.py` - Entry points: `completion()`, `acompletion()`, `embedding()`
- `utils.py` - `get_llm_provider()` resolves model → provider
- `llms/custom_httpx/llm_http_handler.py` - Central HTTP orchestrator
- `llms/custom_httpx/http_handler.py` - Low-level HTTP client
- `llms/{provider}/chat/transformation.py` - Provider-specific transformations
- `litellm_core_utils/streaming_handler.py` - Streaming response handling
- `integrations/` - Async callbacks (Langfuse, Datadog, etc.)
**LLM-specific proxy endpoints:**
---
| Endpoint | Directory | Purpose |
|----------|-----------|---------|
| `/v1/messages` | `proxy/anthropic_endpoints/` | Anthropic Messages API |
| `/vertex-ai/*` | `proxy/vertex_ai_endpoints/` | Vertex AI passthrough |
| `/gemini/*` | `proxy/google_endpoints/` | Google AI Studio passthrough |
| `/v1/images/*` | `proxy/image_endpoints/` | Image generation |
| `/v1/batches` | `proxy/batches_endpoints/` | Batch processing |
| `/v1/files` | `proxy/openai_files_endpoints/` | File uploads |
| `/v1/fine_tuning` | `proxy/fine_tuning_endpoints/` | Fine-tuning jobs |
| `/v1/rerank` | `proxy/rerank_endpoints/` | Reranking |
| `/v1/responses` | `proxy/response_api_endpoints/` | OpenAI Responses API |
| `/v1/vector_stores` | `proxy/vector_store_endpoints/` | Vector stores |
| `/*` (passthrough) | `proxy/pass_through_endpoints/` | Direct provider passthrough |
**Proxy Hooks** (`proxy/hooks/__init__.py`):
| Hook | File | Purpose |
|------|------|---------|
| `max_budget_limiter` | `proxy/hooks/max_budget_limiter.py` | Enforce budget limits |
| `parallel_request_limiter` | `proxy/hooks/parallel_request_limiter_v3.py` | Rate limiting per key/user |
| `cache_control_check` | `proxy/hooks/cache_control_check.py` | Cache validation |
| `responses_id_security` | `proxy/hooks/responses_id_security.py` | Response ID validation |
| `litellm_skills` | `proxy/hooks/skills_injection.py` | Skills injection |
To add a new proxy hook, implement `CustomLogger` and register in `PROXY_HOOKS`.
## 2. Translation Layer
## 3. Translation Layer
When a request comes in, it goes through a **translation layer** that converts between API formats.
Each translation is isolated in its own file, making it easy to test and modify independently.
@ -194,7 +213,9 @@ class ProviderConfig(BaseConfig):
The `BaseLLMHTTPHandler` (`llms/custom_httpx/llm_http_handler.py`) calls these methods - you never need to modify the handler itself.
## 3. Adding/Modifying Providers
---
## 4. Adding/Modifying Providers
### To add a new provider: