feat: Add Deepseek support

.env.example

@@ -5,4 +5,5 @@ OPENAI_API_KEY=
 OPENROUTER_API_KEY=
 GOOGLE_API_KEY=
 XAI_API_KEY=
-GROQ_API_KEY=
+GROQ_API_KEY=
+DEEPSEEK_API_KEY=

guides/deepseek.md

@@ -0,0 +1,164 @@
+# DeepSeek
+
+Use DeepSeek AI models through their OpenAI-compatible API.
+
+## Overview
+
+DeepSeek provides powerful language models including:
+
+- **deepseek-chat** - General purpose conversational model
+- **deepseek-reasoner** - Reasoning and problem-solving capabilities
+
+## Prerequisites
+
+1. Sign up at https://platform.deepseek.com/
+2. Create an API key
+3. Add the key to your environment:
+
+   ```bash
+   # .env
+   DEEPSEEK_API_KEY=your-api-key-here
+   ```
+
+## Usage
+
+### Basic Generation
+
+Since DeepSeek models are not yet in the LLMDB catalog, use an inline model spec:
+
+```elixir
+# Using inline model spec (recommended)
+{:ok, response} = ReqLLM.generate_text(
+  %{provider: :deepseek, id: "deepseek-chat"},
+  "Hello, how are you?"
+)
+
+# Or normalize first
+model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-chat"})
+{:ok, response} = ReqLLM.generate_text(model, "Hello!")
+```
+
+### Code Generation
+
+```elixir
+model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-reasoner"})
+
+{:ok, response} = ReqLLM.generate_text(
+  model,
+  "Write a Python function to calculate fibonacci numbers",
+  temperature: 0.2,
+  max_tokens: 2000
+)
+```
+
+### Streaming
+
+```elixir
+model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-chat"})
+
+{:ok, stream} = ReqLLM.stream_text(model, "Tell me a story about space exploration")
+
+for chunk <- stream do
+  IO.write(chunk.text || "")
+end
+```
+
+### With System Context
+
+```elixir
+context = ReqLLM.Context.new([
+  ReqLLM.Context.system("You are a helpful coding assistant."),
+  ReqLLM.Context.user("How do I parse JSON in Elixir?")
+])
+
+model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-reasoner"})
+
+{:ok, response} = ReqLLM.generate_text(model, context)
+```
+
+## Helper Module
+
+For convenience, create a wrapper module:
+
+```elixir
+defmodule MyApp.DeepSeek do
+  def chat(prompt, opts \\ []) do
+    model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-chat"})
+    ReqLLM.generate_text(model, prompt, opts)
+  end
+
+  def think(prompt, opts \\ []) do
+    model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-reasoner"})
+    ReqLLM.generate_text(model, prompt, Keyword.merge([temperature: 0.2], opts))
+  end
+
+  def stream_chat(prompt, opts \\ []) do
+    model = ReqLLM.model!(%{provider: :deepseek, id: "deepseek-chat"})
+    ReqLLM.stream_text(model, prompt, opts)
+  end
+end
+
+# Usage
+MyApp.DeepSeek.chat("Explain quantum computing")
+MyApp.DeepSeek.think("Write a React component for a todo list")
+```
+
+## Configuration
+
+### Environment Variables
+
+- `DEEPSEEK_API_KEY` - Required. Your DeepSeek API key
+
+### Per-Request API Key
+
+```elixir
+ReqLLM.generate_text(
+  %{provider: :deepseek, id: "deepseek-chat"},
+  "Hello!",
+  api_key: "sk-..."
+)
+```
+
+## Available Models
+
+| Model | Use Case | Context Window |
+|-------|----------|----------------|
+| `deepseek-chat` | General conversation, Q&A | 64K tokens |
+| `deepseek-reasoner` | Complex reasoning tasks | 64K tokens |
+
+Check https://platform.deepseek.com/docs for the latest model information.
+
+## Troubleshooting
+
+### `{:error, :not_found}` when using string spec
+
+DeepSeek models are not yet in the LLMDB registry. Use an inline model spec instead:
+
+```elixir
+# ❌ Won't work (model not in LLMDB)
+ReqLLM.generate_text("deepseek:deepseek-chat", "Hello!")
+
+# ✅ Works (inline model spec)
+ReqLLM.generate_text(
+  %{provider: :deepseek, id: "deepseek-chat"},
+  "Hello!"
+)
+```
+
+### Authentication Errors
+
+- Ensure `DEEPSEEK_API_KEY` is set in your `.env` file
+- Check that the API key is valid at https://platform.deepseek.com/
+
+### Rate Limits
+
+DeepSeek API has rate limits. If you encounter rate limiting:
+- Implement exponential backoff
+- Consider batching requests
+- Check your plan limits at https://platform.deepseek.com/
+
+## Resources
+
+- [DeepSeek Platform](https://platform.deepseek.com/)
+- [DeepSeek API Documentation](https://platform.deepseek.com/docs)
+- [Model Specs Guide](model-specs.md) - For more on inline model specifications

lib/req_llm/providers/deepseek.ex

@@ -0,0 +1,52 @@
+defmodule ReqLLM.Providers.Deepseek do
+  @moduledoc """
+  DeepSeek AI provider – OpenAI-compatible Chat Completions API.
+
+  ## Implementation
+
+  Uses built-in OpenAI-style encoding/decoding defaults.
+  DeepSeek is fully OpenAI-compatible, so no custom request/response handling is needed.
+
+  ## Authentication
+
+  Requires a DeepSeek API key from https://platform.deepseek.com/
+
+  ## Configuration
+
+      # Add to .env file (automatically loaded)
+      DEEPSEEK_API_KEY=your-api-key
+
+  ## Examples
+
+      # Basic usage
+      ReqLLM.generate_text("deepseek:deepseek-chat", "Hello!")
+
+      # With custom parameters
+      ReqLLM.generate_text("deepseek:deepseek-reasoner", "Write a function",
+        temperature: 0.2,
+        max_tokens: 2000
+      )
+
+      # Streaming
+      ReqLLM.stream_text("deepseek:deepseek-chat", "Tell me a story")
+      |> Enum.each(&IO.write/1)
+
+  ## Models
+
+  DeepSeek offers several models including:
+
+  - `deepseek-chat` - General purpose conversational model
+  - `deepseek-reasoner` - Reasoning and problem-solving
+
+  See https://platform.deepseek.com/docs for full model documentation.
+  """
+
+  use ReqLLM.Provider,
+    id: :deepseek,
+    default_base_url: "https://api.deepseek.com",
+    default_env_key: "DEEPSEEK_API_KEY"
+
+  use ReqLLM.Provider.Defaults
+
+  @provider_schema []
+end

mix.exs

@@ -62,6 +62,7 @@ defmodule ReqLLM.MixProject do
           "guides/ollama.md",
           "guides/amazon_bedrock.md",
           "guides/cerebras.md",
+          "guides/deepseek.md",
           "guides/meta.md",
           "guides/zenmux.md",
           "guides/zai.md",