Add Anthropic LLM support (#185)

* Add Anthropic LLM support

Signed-off-by: droctothorpe <mythicalsunlight@gmail.com>

* Update skypilot link

Signed-off-by: droctothorpe <mythicalsunlight@gmail.com>

* Handle anthropic base_url

Signed-off-by: droctothorpe <mythicalsunlight@gmail.com>

* Address ruff format finding

Signed-off-by: droctothorpe <mythicalsunlight@gmail.com>

---------

Signed-off-by: droctothorpe <mythicalsunlight@gmail.com>

README.md

@@ -201,7 +201,7 @@ LEANN supports RAG on various data sources including documents (`.pdf`, `.txt`,
 
 #### LLM Backend
 
-LEANN supports many LLM providers for text generation (HuggingFace, Ollama, and Any OpenAI compatible API).
+LEANN supports many LLM providers for text generation (HuggingFace, Ollama, Anthropic, and Any OpenAI compatible API).
 
 
 <details>
@@ -269,6 +269,7 @@ Below is a list of base URLs for common providers to get you started.
 | **SiliconFlow** | `https://api.siliconflow.cn/v1`                            |
 | **Zhipu (BigModel)** | `https://open.bigmodel.cn/api/paas/v4/`                |
 | **Mistral AI** | `https://api.mistral.ai/v1`                                |
+| **Anthropic** | `https://api.anthropic.com/v1`                                |
 
 
 
@@ -328,7 +329,7 @@ All RAG examples share these common parameters. **Interactive mode** is availabl
 --embedding-mode MODE        # sentence-transformers, openai, mlx, or ollama
 
 # LLM Parameters (Text generation models)
---llm TYPE                   # LLM backend: openai, ollama, or hf (default: openai)
+--llm TYPE                   # LLM backend: openai, ollama, hf, or anthropic (default: openai)
 --llm-model MODEL            # Model name (default: gpt-4o) e.g., gpt-4o-mini, llama3.2:1b, Qwen/Qwen2.5-1.5B-Instruct
 --thinking-budget LEVEL      # Thinking budget for reasoning models: low/medium/high (supported by o3, o3-mini, GPT-Oss:20b, and other reasoning models)
 
@@ -1057,10 +1058,10 @@ Options:
 leann ask INDEX_NAME [OPTIONS]
 
 Options:
-  --llm {ollama,openai,hf}    LLM provider (default: ollama)
+  --llm {ollama,openai,hf,anthropic}    LLM provider (default: ollama)
-  --model MODEL               Model name (default: qwen3:8b)
+  --model MODEL                         Model name (default: qwen3:8b)
-  --interactive              Interactive chat mode
+  --interactive                         Interactive chat mode
-  --top-k N                  Retrieval count (default: 20)
+  --top-k N                             Retrieval count (default: 20)
 ```
 
 **List Command:**

docs/configuration-guide.md

@@ -454,7 +454,7 @@ leann search my-index "your query" \
 
 ### 2) Run remote builds with SkyPilot (cloud GPU)
 
-Offload embedding generation and index building to a GPU VM using [SkyPilot](https://skypilot.readthedocs.io/en/latest/). A template is provided at `sky/leann-build.yaml`.
+Offload embedding generation and index building to a GPU VM using [SkyPilot](https://docs.skypilot.co/en/latest/docs/index.html). A template is provided at `sky/leann-build.yaml`.
 
 ```bash
 # One-time: install and configure SkyPilot

packages/leann-core/src/leann/chat.py

@@ -12,7 +12,13 @@ from typing import Any, Optional
 
 import torch
 
-from .settings import resolve_ollama_host, resolve_openai_api_key, resolve_openai_base_url
+from .settings import (
+    resolve_anthropic_api_key,
+    resolve_anthropic_base_url,
+    resolve_ollama_host,
+    resolve_openai_api_key,
+    resolve_openai_base_url,
+)
 
 # Configure logging
 logging.basicConfig(level=logging.INFO)
@@ -845,6 +851,81 @@ class OpenAIChat(LLMInterface):
             return f"Error: Could not get a response from OpenAI. Details: {e}"
 
 
+class AnthropicChat(LLMInterface):
+    """LLM interface for Anthropic Claude models."""
+
+    def __init__(
+        self,
+        model: str = "claude-haiku-4-5",
+        api_key: Optional[str] = None,
+        base_url: Optional[str] = None,
+    ):
+        self.model = model
+        self.base_url = resolve_anthropic_base_url(base_url)
+        self.api_key = resolve_anthropic_api_key(api_key)
+
+        if not self.api_key:
+            raise ValueError(
+                "Anthropic API key is required. Set ANTHROPIC_API_KEY environment variable or pass api_key parameter."
+            )
+
+        logger.info(
+            "Initializing Anthropic Chat with model='%s' and base_url='%s'",
+            model,
+            self.base_url,
+        )
+
+        try:
+            import anthropic
+
+            # Allow custom Anthropic-compatible endpoints via base_url
+            self.client = anthropic.Anthropic(
+                api_key=self.api_key,
+                base_url=self.base_url,
+            )
+        except ImportError:
+            raise ImportError(
+                "The 'anthropic' library is required for Anthropic models. Please install it with 'pip install anthropic'."
+            )
+
+    def ask(self, prompt: str, **kwargs) -> str:
+        logger.info(f"Sending request to Anthropic with model {self.model}")
+
+        try:
+            # Anthropic API parameters
+            params = {
+                "model": self.model,
+                "max_tokens": kwargs.get("max_tokens", 1000),
+                "messages": [{"role": "user", "content": prompt}],
+            }
+
+            # Add optional parameters
+            if "temperature" in kwargs:
+                params["temperature"] = kwargs["temperature"]
+            if "top_p" in kwargs:
+                params["top_p"] = kwargs["top_p"]
+
+            response = self.client.messages.create(**params)
+
+            # Extract text from response
+            response_text = response.content[0].text
+
+            # Log token usage
+            print(
+                f"Total tokens = {response.usage.input_tokens + response.usage.output_tokens}, "
+                f"input tokens = {response.usage.input_tokens}, "
+                f"output tokens = {response.usage.output_tokens}"
+            )
+
+            if response.stop_reason == "max_tokens":
+                print("The query is exceeding the maximum allowed number of tokens")
+
+            return response_text.strip()
+        except Exception as e:
+            logger.error(f"Error communicating with Anthropic: {e}")
+            return f"Error: Could not get a response from Anthropic. Details: {e}"
+
+
 class SimulatedChat(LLMInterface):
     """A simple simulated chat for testing and development."""
 
@@ -897,6 +978,12 @@ def get_llm(llm_config: Optional[dict[str, Any]] = None) -> LLMInterface:
         )
     elif llm_type == "gemini":
         return GeminiChat(model=model or "gemini-2.5-flash", api_key=llm_config.get("api_key"))
+    elif llm_type == "anthropic":
+        return AnthropicChat(
+            model=model or "claude-3-5-sonnet-20241022",
+            api_key=llm_config.get("api_key"),
+            base_url=llm_config.get("base_url"),
+        )
     elif llm_type == "simulated":
         return SimulatedChat()
     else:

packages/leann-core/src/leann/cli.py

@@ -11,7 +11,12 @@ from tqdm import tqdm
 from .api import LeannBuilder, LeannChat, LeannSearcher
 from .interactive_utils import create_cli_session
 from .registry import register_project_directory
-from .settings import resolve_ollama_host, resolve_openai_api_key, resolve_openai_base_url
+from .settings import (
+    resolve_anthropic_base_url,
+    resolve_ollama_host,
+    resolve_openai_api_key,
+    resolve_openai_base_url,
+)
 
 
 def extract_pdf_text_with_pymupdf(file_path: str) -> str:
@@ -291,7 +296,7 @@ Examples:
             "--llm",
             type=str,
             default="ollama",
-            choices=["simulated", "ollama", "hf", "openai"],
+            choices=["simulated", "ollama", "hf", "openai", "anthropic"],
             help="LLM provider (default: ollama)",
         )
         ask_parser.add_argument(
@@ -341,7 +346,7 @@ Examples:
             "--api-key",
             type=str,
             default=None,
-            help="API key for OpenAI-compatible APIs (defaults to OPENAI_API_KEY)",
+            help="API key for cloud LLM providers (OpenAI, Anthropic)",
         )
 
         # List command
@@ -1616,6 +1621,12 @@ Examples:
             resolved_api_key = resolve_openai_api_key(args.api_key)
             if resolved_api_key:
                 llm_config["api_key"] = resolved_api_key
+        elif args.llm == "anthropic":
+            # For Anthropic, pass base_url and API key if provided
+            if args.api_base:
+                llm_config["base_url"] = resolve_anthropic_base_url(args.api_base)
+            if args.api_key:
+                llm_config["api_key"] = args.api_key
 
         chat = LeannChat(index_path=index_path, llm_config=llm_config)
 

packages/leann-core/src/leann/settings.py

@@ -9,6 +9,7 @@ from typing import Any
 # Default fallbacks to preserve current behaviour while keeping them in one place.
 _DEFAULT_OLLAMA_HOST = "http://localhost:11434"
 _DEFAULT_OPENAI_BASE_URL = "https://api.openai.com/v1"
+_DEFAULT_ANTHROPIC_BASE_URL = "https://api.anthropic.com"
 
 
 def _clean_url(value: str) -> str:
@@ -52,6 +53,23 @@ def resolve_openai_base_url(explicit: str | None = None) -> str:
     return _clean_url(_DEFAULT_OPENAI_BASE_URL)
 
 
+def resolve_anthropic_base_url(explicit: str | None = None) -> str:
+    """Resolve the base URL for Anthropic-compatible services."""
+
+    candidates = (
+        explicit,
+        os.getenv("LEANN_ANTHROPIC_BASE_URL"),
+        os.getenv("ANTHROPIC_BASE_URL"),
+        os.getenv("LOCAL_ANTHROPIC_BASE_URL"),
+    )
+
+    for candidate in candidates:
+        if candidate:
+            return _clean_url(candidate)
+
+    return _clean_url(_DEFAULT_ANTHROPIC_BASE_URL)
+
+
 def resolve_openai_api_key(explicit: str | None = None) -> str | None:
     """Resolve the API key for OpenAI-compatible services."""
 
@@ -61,6 +79,15 @@ def resolve_openai_api_key(explicit: str | None = None) -> str | None:
     return os.getenv("OPENAI_API_KEY")
 
 
+def resolve_anthropic_api_key(explicit: str | None = None) -> str | None:
+    """Resolve the API key for Anthropic services."""
+
+    if explicit:
+        return explicit
+
+    return os.getenv("ANTHROPIC_API_KEY")
+
+
 def encode_provider_options(options: dict[str, Any] | None) -> str | None:
     """Serialize provider options for child processes."""