docs: remove haystack-experimental documentation (#12177)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: David S. Batista <dsbatista@gmail.com>

Author: 3 people

.github/workflows/auto_approve_api_ref_sync.yml

@@ -1,7 +1,6 @@
 name: Approve and merge API reference sync PRs
 
-# Automatically approve and merge API reference sync PRs from Haystack, Haystack Core Integrations,
-# and Haystack Experimental
+# Automatically approve and merge API reference sync PRs from Haystack and Haystack Core Integrations
 
 on:
   pull_request:

docs-website/docs/concepts/experimental-package.mdx

@@ -42,7 +42,7 @@ Here's a table of key concepts and their approximate equivalents between the two
 | Tool (Langchain) | [Tool](../tools/tool.mdx) / [PipelineTool](../tools/pipelinetool.mdx) / [ComponentTool](../tools/componenttool.mdx) / [MCPTool](../tools/mcptool.mdx) | Haystack exposes Python functions, pipelines, components,  external APIs and MCP servers as agent tools. |
 | Multi-Agent Collaboration (LangChain) | Multi-Agent System | Using [`ComponentTool`](../tools/componenttool.mdx), agents can use other agents as tools, enabling [multi-agent architectures](https://haystack.deepset.ai/tutorials/45_creating_a_multi_agent_system) within one framework. |
 | Model Context Protocol `load_mcp_tools` `MultiServerMCPClient` | Model Context Protocol - `MCPTool`, `MCPToolset`, `StdioServerInfo`, `StreamableHttpServerInfo` | Haystack provides [various MCP primitives](https://haystack.deepset.ai/integrations/mcp) for connecting multiple MCP servers and organizing MCP toolsets. |
-| Memory (State, short-term, long-term) | Memory (Agent State, short-term, long-term) | Agent [State](../pipeline-components/agents-1/state.mdx) provides a structured way to share data between tools and store intermediate results during agent execution. For short-term memory, Haystack offers a [ChatMessage Store](/reference/experimental-chatmessage-store-api) to persist chat history. More memory options are coming soon. |
+| Memory (State, short-term, long-term) | Memory (Agent State, short-term, long-term) | Agent [State](../pipeline-components/agents-1/state.mdx) provides a structured way to share data between tools and store intermediate results during agent execution. For long-term memory, Haystack offers memory stores such as [Mem0MemoryStore](../memory-stores/mem0memorystore.mdx) and [CogneeMemoryStore](../memory-stores/cogneememorystore.mdx) to persist conversation history across sessions. |
 | Time travel (Checkpoints) | Breakpoints (Breakpoint, PipelineSnapshot) | [Breakpoints](../concepts/pipelines/pipeline-breakpoints.mdx) let you pause, inspect, modify, and resume a pipeline for debugging or iterative development. |
 | Human-in-the-Loop (Interrupts / Commands) | Human-in-the-loop (`ConfirmationHook` with confirmation strategies) | Haystack applies [confirmation strategies](https://haystack.deepset.ai/tutorials/47_human_in_the_loop_agent) through a `ConfirmationHook` registered under the Agent's `before_tool` [hook point](../pipeline-components/agents-1/hooks.mdx) to pause or block the execution to gather user feedback |
 

docs-website/docs/overview/migrating-from-langgraphlangchain-to-haystack.mdx

@@ -27,7 +27,7 @@ pip install --upgrade haystack-ai
 
 Two dependency changes to be aware of:
 
-- **`haystack-experimental` is no longer installed automatically.** If your code imports from `haystack_experimental`, install it explicitly with `pip install haystack-experimental`.
+- **`haystack-experimental` is no longer installed automatically.** The package is now archived and unmaintained: `0.19.0.post1` is its final release. If your code still imports from `haystack_experimental`, install it explicitly and pin it with `pip install "haystack-experimental==0.19.0.post1"`. Most experiments graduated into `haystack-ai` itself, so prefer migrating your imports to the core equivalents.
 - **Several components moved to dedicated integration packages** and now require an extra `pip install`. See [Components Moved to Integration Packages](#components-moved-to-integration-packages) below.
 
 ## Removed and Renamed Components

docs-website/docs/overview/migration.mdx

@@ -83,7 +83,7 @@ This is an example of a RAG Haystack pipeline. It first retrieves leaf-level doc
 ```python
 from typing import List, Tuple
 from haystack import Document, Pipeline
-from haystack_experimental.components.splitters import HierarchicalDocumentSplitter
+from haystack.components.preprocessors import HierarchicalDocumentSplitter
 from haystack.components.builders.answer_builder import AnswerBuilder
 from haystack.components.builders.chat_prompt_builder import ChatPromptBuilder
 from haystack.components.generators.chat import OpenAIChatGenerator

docs-website/docs/pipeline-components/retrievers/automergingretriever.mdx

@@ -21,11 +21,5 @@ export default {
       link: { type: 'generated-index', title: 'Integrations API' },
       items: [{ type: 'autogenerated', dirName: 'integrations-api' }],
     },
-    {
-      type: 'category',
-      label: 'Experiments API',
-      link: { type: 'generated-index', title: 'Experiments API' },
-      items: [{ type: 'autogenerated', dirName: 'experiments-api' }],
-    },
   ],
 };