Add OpenRouter integration (#325)

* Add openrouter

* Update openrouter.md

---------

Co-authored-by: Bilge Yücel <bilge.yucel@deepset.ai>

Author: Amnah199

integrations/openrouter.md

@@ -0,0 +1,100 @@
+---
+layout: integration
+name: OpenRouter
+description: Use the OpenRouter API for text generation models.
+authors:
+    - name: deepset 
+      socials:
+        github: deepset-ai
+        twitter: deepset_ai
+        linkedin: https://www.linkedin.com/company/deepset-ai/
+pypi: https://pypi.org/project/openrouter-haystack
+repo: https://github.com/deepset-ai/haystack-core-integrations/tree/main/integrations/openrouter
+type: Model Provider
+report_issue: https://github.com/deepset-ai/haystack-core-integrations/issues
+logo: /logos/openrouter.png
+version: Haystack 2.0
+toc: true
+---
+
+### **Table of Contents**
+- [Overview](#overview)
+- [Installation](#installation)
+- [Usage](#usage)
+- [License](#license)
+
+## Overview
+
+`OpenRouterChatGenerator` lets you call any LLMs available on [OpenRouter](https://openrouter.ai), including:
+
+- OpenAI variants such as `openai/gpt-4o`
+- Anthropic’s `claude-3.5-sonnet`
+- Community-hosted open-source models (Llama 2, Mixtral, etc.)
+
+For more information on models available via the OpenRouter API, see [the OpenRouter docs](https://openrouter.ai/models).
+
+In addition to basic chat completion, the component exposes OpenRouter-specific features:
+
+* **Provider / model routing** – choose fallback models or provider ordering with the `generation_kwargs` parameter.
+* **Extra HTTP headers** – add attribution or tracing headers via `extra_headers`.
+
+
+In order to follow along with this guide, you'll need a OpenRouter API key. Add it as an environment variable, `OPENROUTER_API_KEY`.
+
+## Installation
+
+```bash
+pip install openrouter-haystack
+```
+
+## Usage
+You can use [OpenRouterChatGenerator](https://docs.haystack.deepset.ai/docs/openrouterchatgenerator) as standalone, within a [pipeline](https://docs.haystack.deepset.ai/docs/pipelines) or with the [Agent component](https://docs.haystack.deepset.ai/docs/agent).
+
+Here's an example of using it as a standalone component:
+
+```python
+import os
+from haystack.dataclasses import ChatMessage
+from haystack_integrations.components.generators.openrouter import OpenRouterChatGenerator
+
+os.environ["OPENROUTER_API_KEY"] = "YOUR_OPENROUTER_API_KEY"
+
+client = OpenRouterChatGenerator() # defaults to openai/gpt-4o-mini
+response = client.run(
+    [ChatMessage.from_user("What are Agentic Pipelines? Be brief.")]
+)
+print(response["replies"])
+
+```
+```bash
+{'replies': [ChatMessage(_role=<ChatRole.ASSISTANT: 'assistant'>, _content=[TextContent(text='The capital of Vietnam is Hanoi.')], _name=None, _meta={'model': 'openai/gpt-4o-mini', 'index': 0, 'finish_reason': 'stop', 'usage': {'completion_tokens': 8, 'prompt_tokens': 13, 'total_tokens': 21, 'completion_tokens_details': CompletionTokensDetails(accepted_prediction_tokens=None, audio_tokens=None, reasoning_tokens=0, rejected_prediction_tokens=None), 'prompt_tokens_details': PromptTokensDetails(audio_tokens=None, cached_tokens=0)}})]}
+```
+`OpenRouterChatGenerator` also support streaming responses if you pass a streaming callback:
+
+```python
+import os
+from haystack.dataclasses import ChatMessage
+from haystack_integrations.components.generators.openrouter import OpenRouterChatGenerator
+
+os.environ["OPENROUTER_API_KEY"] = "YOUR_OPENROUTER_API_KEY"
+
+def show(chunk):                              # simple streaming callback
+    print(chunk.content, end="", flush=True)
+
+client = OpenRouterChatGenerator(
+    model="openrouter/auto",                  # let OpenRouter pick a model
+    streaming_callback=show,
+    generation_kwargs={
+        "provider": {"sort": "throughput"},   # pick the fastest provider
+    }
+)
+
+response = client.run([ChatMessage.from_user("Summarize RAG in two lines.")])
+
+print (response)
+
+```
+
+### License
+
+`openrouter-haystack` is distributed under the terms of the [Apache-2.0](https://spdx.org/licenses/Apache-2.0.html) license.