diff --git a/gradle/runtime.libs.versions.toml b/gradle/runtime.libs.versions.toml
index a49713084..560de2a79 100644
--- a/gradle/runtime.libs.versions.toml
+++ b/gradle/runtime.libs.versions.toml
@@ -19,7 +19,6 @@ access-transformers-new = "8.0.5"
 access-transformers-neo = "10.0.2"
 unprotect = "1.2.0"
 asm = "9.7"
-union-relauncher = "1.1.1"
 access-transformers-log4j = "2.17.1"
 
 [libraries]
@@ -45,5 +44,4 @@ access-transformers-new = { module = "net.minecraftforge:accesstransformers", ve
 access-transformers-neo = { module = "net.neoforged.accesstransformers:at-cli", version.ref = "access-transformers-neo" }
 unprotect = { module = "io.github.juuxel:unprotect", version.ref = "unprotect" }
 asm = { module = "org.ow2.asm:asm", version.ref = "asm" }
-union-relauncher = { module = "io.github.juuxel:union-relauncher", version.ref = "union-relauncher" }
 access-transformers-log4j-bom = { module = "org.apache.logging.log4j:log4j-bom", version.ref = "access-transformers-log4j" }
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
index 7243f27d1..66d5b0932 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
@@ -96,6 +96,13 @@ public static void provide(MappingConfiguration mappingConfiguration, Project pr
 				}
 			}
 
+			if (lib.startsWith("net.minecraftforge:bootstrap:")) {
+				if (extension.isForge() && extension.getForgeProvider().getVersion().getMajorVersion() >= Constants.Forge.MIN_BOOTSTRAP_DEV_VERSION) {
+					String version = lib.substring(lib.lastIndexOf(":"));
+					dependencies.add(project.getDependencies().create("net.minecraftforge:bootstrap-dev" + version));
+				}
+			}
+
 			if (dep == null) {
 				dep = lib;
 			}
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeProvider.java
index b62a9d1cc..1be328d04 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeProvider.java
@@ -32,7 +32,6 @@
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.configuration.DependencyInfo;
 import net.fabricmc.loom.util.Constants;
-import net.fabricmc.loom.util.LoomVersions;
 import net.fabricmc.loom.util.ModPlatform;
 
 public class ForgeProvider extends DependencyProvider {
@@ -50,10 +49,6 @@ public void provide(DependencyInfo dependency) throws Exception {
 		version = new ForgeVersion(dependency.getResolvedVersion());
 		addDependency(dependency.getDepString() + ":userdev", Constants.Configurations.FORGE_USERDEV);
 		addDependency(dependency.getDepString() + ":installer", Constants.Configurations.FORGE_INSTALLER);
-
-		if (getExtension().isForge() && version.getMajorVersion() >= Constants.Forge.MIN_UNION_RELAUNCHER_VERSION) {
-			addDependency(LoomVersions.UNION_RELAUNCHER.mavenNotation(), Constants.Configurations.FORGE_EXTRA);
-		}
 	}
 
 	public ForgeVersion getVersion() {
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunTemplate.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunTemplate.java
index 3f56b844f..624a2630a 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunTemplate.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunTemplate.java
@@ -112,13 +112,6 @@ public void applyTo(RunConfigSettings settings, ConfigValue.Resolver configValue
 
 		// Add MOD_CLASSES, this is something that ForgeGradle does
 		settings.getEnvironmentVariables().computeIfAbsent("MOD_CLASSES", $ -> ConfigValue.of("{source_roots}").resolve(configValueResolver));
-
-		final ForgeProvider forgeProvider = settings.getExtension().getForgeProvider();
-
-		if (settings.getExtension().isForge() && forgeProvider.getVersion().getMajorVersion() >= Constants.Forge.MIN_UNION_RELAUNCHER_VERSION) {
-			settings.defaultMainClass(Constants.Forge.UNION_RELAUNCHER_MAIN_CLASS);
-			settings.property(Constants.Forge.UNION_RELAUNCHER_MAIN_CLASS_PROPERTY, main);
-		}
 	}
 
 	public Resolved resolve(ConfigValue.Resolver configValueResolver) {
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunsProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunsProvider.java
index 0fe3953ce..c44b45377 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunsProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunsProvider.java
@@ -128,6 +128,8 @@ private String resolve(@Nullable RunConfigSettings runConfig, ConfigValue.Variab
 			// Use a set-valued multimap for deduplicating paths.
 			Multimap<String, String> modClasses = MultimapBuilder.hashKeys().linkedHashSetValues().build();
 			NamedDomainObjectContainer<ModSettings> mods = extension.getMods();
+			// Forge 49+ bootstrap-dev uses ; as a separator, instead of File.pathSeparator
+			String separator = extension.getForgeProvider().getVersion().getMajorVersion() >= Constants.Forge.MIN_BOOTSTRAP_DEV_VERSION ? ";" : File.pathSeparator;
 
 			if (runConfig != null && !runConfig.getMods().isEmpty()) {
 				mods = runConfig.getMods();
@@ -147,7 +149,7 @@ private String resolve(@Nullable RunConfigSettings runConfig, ConfigValue.Variab
 
 			string = modClasses.entries().stream()
 					.map(entry -> entry.getKey() + "%%" + entry.getValue())
-					.collect(Collectors.joining(File.pathSeparator));
+					.collect(Collectors.joining(separator));
 		} else if (key.equals("mcp_mappings")) {
 			string = "loom.stub";
 		} else if (json.has(key)) {
diff --git a/src/main/java/net/fabricmc/loom/util/Constants.java b/src/main/java/net/fabricmc/loom/util/Constants.java
index 14530ddac..237678f3b 100644
--- a/src/main/java/net/fabricmc/loom/util/Constants.java
+++ b/src/main/java/net/fabricmc/loom/util/Constants.java
@@ -192,11 +192,9 @@ public static final class Forge {
 		public static final String MIXIN_CONFIGS_MANIFEST_KEY = "MixinConfigs";
 
 		/**
-		 * The minimum Forge version that needs Union Relauncher to use {@code MOD_CLASSES}.
+		 * The minimum Forge version that needs bootstrap-dev to use {@code MOD_CLASSES}.
 		 */
-		public static final int MIN_UNION_RELAUNCHER_VERSION = 49;
-		public static final String UNION_RELAUNCHER_MAIN_CLASS = "juuxel.unionrelauncher.UnionRelauncher";
-		public static final String UNION_RELAUNCHER_MAIN_CLASS_PROPERTY = "unionRelauncher.mainClass";
+		public static final int MIN_BOOTSTRAP_DEV_VERSION = 49;
 
 		/**
 		 * The minimum version of Forge that uses "mojang" as the namespace in production.