diff --git a/tests/Elastic.Markdown.Tests/CrossLinks/LinksJsonForwardCompatibilityTests.cs b/tests/Elastic.Markdown.Tests/CrossLinks/LinksJsonForwardCompatibilityTests.cs
new file mode 100644
index 0000000000..8099aedfb4
--- /dev/null
+++ b/tests/Elastic.Markdown.Tests/CrossLinks/LinksJsonForwardCompatibilityTests.cs
@@ -0,0 +1,129 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Collections.Frozen;
+using AwesomeAssertions;
+using Elastic.Documentation.Links;
+using Elastic.Documentation.Links.CrossLinks;
+
+namespace Elastic.Markdown.Tests.CrossLinks;
+
+/// <summary>
+/// <c>links.json</c> is published by one build and read by every other build, including builds of older versions of
+/// docs-builder. A newer build can add properties, such as the pages of an API. An older reader must ignore what it
+/// does not know and read everything else exactly as before.
+/// </summary>
+public class LinksJsonForwardCompatibilityTests
+{
+	private const string Core =
+		// language=json
+		"""
+		"origin": { "branch": "main", "remote": "https://github.com/elastic/docs-content", "ref": "76aac68d066e2af935c38bca8ce04d3ee67a8dd9" },
+		"url_path_prefix": "/elastic/docs-content/tree/main",
+		"cross_links": [ "kibana://index.md" ],
+		"links": {
+		  "index.md": {},
+		  "get-started/index.md": { "anchors": [ "intro", "use-cases" ] },
+		  "hidden-page.md": { "hidden": true }
+		},
+		"redirects": { "old.md": { "to": "get-started/index.md" } }
+		""";
+
+	private static string WithProperty(string property) => "{" + Core + "," + property + "}";
+
+	/// <summary>The section a later build writes for an API: each version states its root, and each page names the versions that contain it.</summary>
+	private const string FloatingSection =
+		// language=json
+		"""
+		"floating": {
+		  "api/elasticsearch": {
+		    "versions": [
+		      { "name": "8", "root": "api/doc/elasticsearch/v8", "hidden": true },
+		      { "name": "main", "root": "api/doc/elasticsearch", "current": true }
+		    ],
+		    "pages": { "": 3, "operation/operation-search": 3, "operation/operation-new": 2 },
+		    "aliases": { "8": { "operation/operation-search": [ "operation/operation-search-1" ] } }
+		  }
+		}
+		""";
+
+	public static IEnumerable<string> FutureProperties() =>
+		[
+			FloatingSection,
+			// language=json
+			"\"floating\": \"a string\"",
+			// language=json
+			"\"floating\": 42",
+			// language=json
+			"\"floating\": [ 1, 2, { \"nested\": [ true, null ] } ]",
+			// language=json
+			"\"floating\": { \"api/elasticsearch\": { \"versions\": [ { \"name\": \"main\", \"unheard_of\": [ 1 ] } ], \"something_new\": {} } }",
+			// language=json
+			"\"some_other_future_property\": { \"a\": 1 }"
+		];
+
+	private static void AssertReadsTheDocumentedProperties(RepositoryLinks links)
+	{
+		links.Origin.Branch.Should().Be("main");
+		links.UrlPathPrefix.Should().Be("/elastic/docs-content/tree/main");
+		links.CrossLinks.Should().Equal("kibana://index.md");
+		links.Links.Keys.Should().BeEquivalentTo("index.md", "get-started/index.md", "hidden-page.md");
+		links.Links["get-started/index.md"].Anchors.Should().Equal("intro", "use-cases");
+		links.Links["hidden-page.md"].Hidden.Should().BeTrue();
+		links.Redirects.Should().ContainKey("old.md").WhoseValue.To.Should().Be("get-started/index.md");
+	}
+
+	[Test]
+	[MethodDataSource(nameof(FutureProperties))]
+	public void Deserialize_WithAPropertyAnOlderReaderDoesNotKnow_ReadsTheRestUnchanged(string property) =>
+		AssertReadsTheDocumentedProperties(RepositoryLinks.Deserialize(WithProperty(property)));
+
+	[Test]
+	public void Deserialize_WithAndWithoutAFloatingSection_GivesTheSameLinks()
+	{
+		var without = RepositoryLinks.Deserialize("{" + Core + "}");
+		var with = RepositoryLinks.Deserialize(WithProperty(FloatingSection));
+
+		with.Links.Should().BeEquivalentTo(without.Links);
+		with.Redirects.Should().BeEquivalentTo(without.Redirects);
+		with.CrossLinks.Should().Equal(without.CrossLinks);
+		with.Origin.Should().Be(without.Origin);
+	}
+
+	[Test]
+	public void CrossLinkFetcher_Deserialize_WithAFloatingSection_ReadsTheRest() =>
+		AssertReadsTheDocumentedProperties(CrossLinkFetcher.Deserialize(WithProperty(FloatingSection)));
+
+	[Test]
+	[Arguments("docs-content://index.md", true)]
+	[Arguments("docs-content://get-started/index.md#intro", true)]
+	[Arguments("docs-content://get-started/index.md#missing-anchor", false)]
+	[Arguments("docs-content://does-not-exist.md", false)]
+	public void CrossLinks_WithAFloatingSectionInTheTargetLinks_ResolveAsBefore(string crossLink, bool expected)
+	{
+		var resolve = (RepositoryLinks links) =>
+		{
+			var fetched = new FetchedCrossLinks
+			{
+				DeclaredRepositories = ["docs-content"],
+				LinkReferences = new Dictionary<string, RepositoryLinks> { ["docs-content"] = links }.ToFrozenDictionary(),
+				LinkIndexEntries = new Dictionary<string, LinkRegistryEntry>().ToFrozenDictionary()
+			};
+			var resolved = CrossLinkResolver.TryResolve(
+				_ => { },
+				fetched,
+				new IsolatedBuildEnvironmentUriResolver(),
+				new Uri(crossLink),
+				out var uri
+			);
+			return (resolved, uri?.ToString());
+		};
+
+		var without = resolve(RepositoryLinks.Deserialize("{" + Core + "}"));
+		var with = resolve(RepositoryLinks.Deserialize(WithProperty(FloatingSection)));
+
+		with.resolved.Should().Be(expected);
+		with.Should().Be(without, "a floating section changes nothing for pages that are not part of it");
+	}
+}