Update documentation

Author: flobernd

README.md

@@ -2,7 +2,6 @@
 
 Repository for **Elastic.Clients.Elasticsearch** the official .NET client for
 [Elasticsearch](https://github.com/elastic/elasticsearch).
-*Older branches include both previous clients, **NEST** and **Elasticsearch.Net**.*
 
 **[Download the latest version of Elasticsearch](https://www.elastic.co/downloads/elasticsearch)**
 or
@@ -61,40 +60,13 @@ for comprehensive information on installation, configuration and usage.
 
 The API reference documentation is available [here](https://elastic.github.io/elasticsearch-net).
 
-## Versions
-
-### Elasticsearch 8.x Clusters
-
-We have released the next generation of the .NET client for Elasticsearch, which
-aligns with v8 of Elasticsearch. We have renamed this library
-`Elastic.Clients.Elasticsearch`, and the packages are published on
-[NuGet](https://www.nuget.org/packages/Elastic.Clients.Elasticsearch/). The
-8.0.x versions do not offer complete feature parity with the existing `NEST`
-client. We therefore recommend you thoroughly review our
-[release notes and migration guidance](https://www.elastic.co/guide/en/elasticsearch/client/net-api/current/release-notes-8.0.0.html)
-before attempting to migrate existing applications to the
-`Elastic.Clients.Elasticsearch` library.
-
-Until the new client supports all endpoints and features your application
-requires, you may continue to use the latest `7.17.x` client to communicate with
-Elasticsearch v8 servers. Please review
-[our documentation](https://www.elastic.co/guide/en/elasticsearch/client/net-api/7.17/connecting-to-elasticsearch-v8.html),
-which describes how to enable compatibility mode and secure communications with
-a v8 cluster.
-
-### Elasticsearch 7.x Clusters
-
-We recommend using the latest `7.17.x`
-[NEST client](https://www.nuget.org/packages/Nest) to communicate with
-Elasticsearch v7 servers.
-
 ## Contributing
 
 See [CONTRIBUTING.md](./CONTRIBUTING.md)
 
 ## Copyright and License
 
-This software is Copyright (c) 2014-2022 by Elasticsearch BV.
+This software is Copyright (c) 2014-2025 by Elasticsearch BV.
 
 This is free software, licensed under
 [The Apache License Version 2.0](https://github.com/elastic/elasticsearch-net/blob/main/LICENSE.txt).

docs/reference/index.md

@@ -10,10 +10,7 @@ mapped_pages:
 
 Designed for .NET application developers, the .NET language client library provides a strongly typed API and query DSL for interacting with {{es}}. The .NET client includes higher-level abstractions, such as helpers for coordinating bulk indexing and update operations. It also comes with built-in, configurable cluster failover retry mechanisms.
 
-The {{es}} .NET client is available as a [NuGet](https://www.nuget.org/packages/Elastic.Clients.Elasticsearch) package for use with .NET Core, .NET 5+, and .NET Framework (4.6.1 and later) applications.
-
-*NOTE: This documentation covers the v8 .NET client for {{es}}, for use with {{es}} 8.x versions. To develop applications targeting {{es}} v7, use the [v7 (NEST) client](https://www.elastic.co/guide/en/elasticsearch/client/net-api/7.17).*
-
+The {{es}} .NET client is available as a [NuGet](https://www.nuget.org/packages/Elastic.Clients.Elasticsearch) package
 
 ## Features [features]
 
@@ -30,15 +27,29 @@ The .NET {{es}} client is built on the Elastic Transport library, which provides
 * Connection management and load balancing across all available nodes.
 * Request retries and dead connections handling.
 
-
 ## {{es}} version compatibility [_es_version_compatibility]
 
-Language clients are forward compatible: clients support communicating with current and later minor versions of {{es}}. {{es}} language clients are backward compatible with default distributions only and without guarantees.
+Language clients are **forward compatible**:
+
+Given a constant major version of the client, each related minor version is compatible with its equivalent- and all later {{es}} minor versions of the **same or next higher** major version.
+
+For example:
 
+| Client Version | Compatible with {{es}} `8.x` | Compatible with {{es}} `9.x` | Compatible with {{es}} `10.x` |
+| ---: | :-- | :-- | :-- |
+| 9.x | ❌ no | ✅ yes | ✅ yes |
+| 8.x | ✅ yes | ✅ yes | ❌ no |
+
+Language clients are also **backward compatible** across minor versions within the **same** major version (without strong guarantees), but **never** backward compatible with earlier {{es}} major versions.
+
+:::{note}
+
+Compatibility does not imply feature parity. For example, an `8.12` client is compatible with `8.13`, but does not support any of the new features introduced in {{es}} `8.13`.
+
+:::
 
 ## Questions, bugs, comments, feature requests [_questions_bugs_comments_feature_requests]
 
 To submit a bug report or feature request, use [GitHub issues](https://github.com/elastic/elasticsearch-net/issues).
 
 For more general questions and comments, try the community forum on [discuss.elastic.co](https://discuss.elastic.co/c/elasticsearch). Mention `.NET` in the title to indicate the discussion topic.
-