diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
index b5f4b68..de6c5de 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredTargetFactory.java
@@ -180,7 +180,7 @@
       ConfiguredTargetKey configuredTargetKey,
       OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
       ImmutableMap<Label, ConfigMatchingProvider> configConditions,
-      @Nullable ResolvedToolchainContext toolchainContext)
+      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts)
       throws InterruptedException, ActionConflictException {
     if (target instanceof Rule) {
       try {
@@ -193,7 +193,7 @@
             configuredTargetKey,
             prerequisiteMap,
             configConditions,
-            toolchainContext);
+            toolchainContexts);
       } finally {
         CurrentRuleTracker.endConfiguredTarget();
       }
@@ -407,7 +407,7 @@
       ConfiguredTargetKey configuredTargetKey,
       OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
       ImmutableMap<Label, ConfigMatchingProvider> configConditions,
-      @Nullable ResolvedToolchainContext toolchainContext)
+      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts)
       throws InterruptedException, ActionConflictException {
     ConfigurationFragmentPolicy configurationFragmentPolicy =
         rule.getRuleClassObject().getConfigurationFragmentPolicy();
@@ -426,7 +426,7 @@
             .setPrerequisites(transformPrerequisiteMap(prerequisiteMap, rule))
             .setConfigConditions(configConditions)
             .setUniversalFragments(ruleClassProvider.getUniversalFragments())
-            .setToolchainContext(toolchainContext)
+            .setToolchainContexts(toolchainContexts)
             .setConstraintSemantics(ruleClassProvider.getConstraintSemantics())
             .setRequiredConfigFragments(
                 getRequiredConfigFragments(
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
index 34fa85b..6fe5f87 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleContext.java
@@ -199,7 +199,7 @@
   private final ConfigurationFragmentPolicy configurationFragmentPolicy;
   private final ImmutableList<Class<? extends BuildConfiguration.Fragment>> universalFragments;
   private final RuleErrorConsumer reporter;
-  @Nullable private final ResolvedToolchainContext toolchainContext;
+  @Nullable private final ToolchainCollection<ResolvedToolchainContext> toolchainContexts;
   private final ConstraintSemantics constraintSemantics;
   private final ImmutableSet<String> requiredConfigFragments;
 
@@ -219,7 +219,7 @@
       String ruleClassNameForLogging,
       ActionLookupValue.ActionLookupKey actionLookupKey,
       ImmutableMap<String, Attribute> aspectAttributes,
-      @Nullable ResolvedToolchainContext toolchainContext,
+      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts,
       ConstraintSemantics constraintSemantics,
       ImmutableSet<String> requiredConfigFragments) {
     super(
@@ -251,7 +251,7 @@
     this.hostConfiguration = builder.hostConfiguration;
     this.actionOwnerSymbolGenerator = new SymbolGenerator<>(actionLookupKey);
     reporter = builder.reporter;
-    this.toolchainContext = toolchainContext;
+    this.toolchainContexts = toolchainContexts;
     this.constraintSemantics = constraintSemantics;
     this.requiredConfigFragments = requiredConfigFragments;
   }
@@ -1224,16 +1224,28 @@
     return configurationMakeVariableContext;
   }
 
+  // TODO(b/151742236): provide access to other non-default toolchain contexts.
   @Nullable
   public ResolvedToolchainContext getToolchainContext() {
-    return toolchainContext;
+    return toolchainContexts == null ? null : toolchainContexts.getDefaultToolchainContext();
+  }
+
+  @Nullable
+  public ToolchainCollection<ResolvedToolchainContext> getToolchainContextsForTesting() {
+    return toolchainContexts;
   }
 
   public boolean targetPlatformHasConstraint(ConstraintValueInfo constraintValue) {
-    if (toolchainContext == null || toolchainContext.targetPlatform() == null) {
+    if (toolchainContexts == null
+        || toolchainContexts.getDefaultToolchainContext().targetPlatform() == null) {
       return false;
     }
-    return toolchainContext.targetPlatform().constraints().hasConstraintValue(constraintValue);
+    // All toolchain contexts should have the same target platform so we access via the default.
+    return toolchainContexts
+        .getDefaultToolchainContext()
+        .targetPlatform()
+        .constraints()
+        .hasConstraintValue(constraintValue);
   }
 
   public ConstraintSemantics getConstraintSemantics() {
@@ -1615,7 +1627,7 @@
     private NestedSet<PackageGroupContents> visibility;
     private ImmutableMap<String, Attribute> aspectAttributes;
     private ImmutableList<Aspect> aspects;
-    private ResolvedToolchainContext toolchainContext;
+    private ToolchainCollection<ResolvedToolchainContext> toolchainContexts;
     private ConstraintSemantics constraintSemantics;
     private ImmutableSet<String> requiredConfigFragments = ImmutableSet.of();
 
@@ -1668,7 +1680,7 @@
           getRuleClassNameForLogging(),
           actionOwnerSymbol,
           aspectAttributes != null ? aspectAttributes : ImmutableMap.<String, Attribute>of(),
-          toolchainContext,
+          toolchainContexts,
           constraintSemantics,
           requiredConfigFragments);
     }
@@ -1728,7 +1740,24 @@
 
     /** Sets the {@link ResolvedToolchainContext} used to access toolchains used by this rule. */
     public Builder setToolchainContext(ResolvedToolchainContext toolchainContext) {
-      this.toolchainContext = toolchainContext;
+      Preconditions.checkState(
+          this.toolchainContexts == null,
+          "toolchainContexts has already been set for this Builder");
+      this.toolchainContexts =
+          new ToolchainCollection.Builder<ResolvedToolchainContext>()
+              .addDefaultContext(toolchainContext)
+              .build();
+      return this;
+    }
+
+    /** Sets the collection of {@link ResolvedToolchainContext}s available to this rule. */
+    @VisibleForTesting
+    public Builder setToolchainContexts(
+        ToolchainCollection<ResolvedToolchainContext> toolchainContexts) {
+      Preconditions.checkState(
+          this.toolchainContexts == null,
+          "toolchainContexts has already been set for this Builder");
+      this.toolchainContexts = toolchainContexts;
       return this;
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ToolchainCollection.java b/src/main/java/com/google/devtools/build/lib/analysis/ToolchainCollection.java
index 1f62133..17985a9 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ToolchainCollection.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ToolchainCollection.java
@@ -13,11 +13,11 @@
 // limitations under the License.
 package com.google.devtools.build.lib.analysis;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.cmdline.Label;
-import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -30,7 +30,7 @@
  *     after toolchain resolution.
  */
 public class ToolchainCollection<T extends ToolchainContext> {
-  private static final String DEFAULT_EXEC_GROUP_NAME = "default_exec_group";
+  @VisibleForTesting public static final String DEFAULT_EXEC_GROUP_NAME = "default_exec_group";
 
   /** A map of execution group names to toolchain contexts. */
   private final ImmutableMap<String, T> toolchainContexts;
@@ -82,7 +82,7 @@
     return new ToolchainCollection<>(ImmutableMap.copyOf(toolchainContexts));
   }
 
-  public Collection<T> getContexts() {
-    return toolchainContexts.values();
+  public ImmutableMap<String, T> getContextMap() {
+    return toolchainContexts;
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
index 72a1821..6d9b644 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ConfiguredTargetFunction.java
@@ -321,16 +321,22 @@
       Preconditions.checkNotNull(depValueMap);
 
       // Load the requested toolchains into the ToolchainContext, now that we have dependencies.
-      // TODO(b/151742236); load non-default {@link ExecGroup} toolchains.
-      ResolvedToolchainContext toolchainContext = null;
+      ToolchainCollection<ResolvedToolchainContext> toolchainContexts = null;
       if (unloadedToolchainContexts != null) {
         String targetDescription = target.toString();
-        toolchainContext =
-            ResolvedToolchainContext.load(
-                target.getPackage().getRepositoryMapping(),
-                unloadedToolchainContexts.getDefaultToolchainContext(),
-                targetDescription,
-                depValueMap.get(DependencyResolver.TOOLCHAIN_DEPENDENCY));
+        ToolchainCollection.Builder<ResolvedToolchainContext> contextsBuilder =
+            new ToolchainCollection.Builder<>();
+        for (Map.Entry<String, UnloadedToolchainContext> unloadedContext :
+            unloadedToolchainContexts.getContextMap().entrySet()) {
+          contextsBuilder.addContext(
+              unloadedContext.getKey(),
+              ResolvedToolchainContext.load(
+                  target.getPackage().getRepositoryMapping(),
+                  unloadedContext.getValue(),
+                  targetDescription,
+                  depValueMap.get(DependencyResolver.TOOLCHAIN_DEPENDENCY)));
+        }
+        toolchainContexts = contextsBuilder.build();
       }
 
       ConfiguredTargetValue ans =
@@ -342,7 +348,7 @@
               configuredTargetKey,
               depValueMap,
               configConditions,
-              toolchainContext,
+              toolchainContexts,
               transitivePackagesForPackageRootResolution);
       if (configuredTargetProgress != null) {
         configuredTargetProgress.doneConfigureTarget();
@@ -916,7 +922,7 @@
       ConfiguredTargetKey configuredTargetKey,
       OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> depValueMap,
       ImmutableMap<Label, ConfigMatchingProvider> configConditions,
-      @Nullable ResolvedToolchainContext toolchainContext,
+      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts,
       @Nullable NestedSetBuilder<Package> transitivePackagesForPackageRootResolution)
       throws ConfiguredTargetFunctionException, InterruptedException {
     StoredEventHandler events = new StoredEventHandler();
@@ -942,7 +948,7 @@
               configuredTargetKey,
               depValueMap,
               configConditions,
-              toolchainContext);
+              toolchainContexts);
     } catch (MissingDepException e) {
       Preconditions.checkState(env.valuesMissing(), e.getMessage());
       return null;
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeBuildView.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeBuildView.java
index 6ac47a74..52be517 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeBuildView.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeBuildView.java
@@ -44,6 +44,7 @@
 import com.google.devtools.build.lib.analysis.ConfiguredTargetFactory;
 import com.google.devtools.build.lib.analysis.DependencyResolver.DependencyKind;
 import com.google.devtools.build.lib.analysis.ResolvedToolchainContext;
+import com.google.devtools.build.lib.analysis.ToolchainCollection;
 import com.google.devtools.build.lib.analysis.TopLevelArtifactContext;
 import com.google.devtools.build.lib.analysis.ViewCreationFailedException;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
@@ -869,7 +870,7 @@
       ConfiguredTargetKey configuredTargetKey,
       OrderedSetMultimap<DependencyKind, ConfiguredTargetAndData> prerequisiteMap,
       ImmutableMap<Label, ConfigMatchingProvider> configConditions,
-      @Nullable ResolvedToolchainContext toolchainContext)
+      @Nullable ToolchainCollection<ResolvedToolchainContext> toolchainContexts)
       throws InterruptedException, ActionConflictException {
     Preconditions.checkState(
         enableAnalysis, "Already in execution phase %s %s", target, configuration);
@@ -885,7 +886,7 @@
         configuredTargetKey,
         prerequisiteMap,
         configConditions,
-        toolchainContext);
+        toolchainContexts);
   }
 
   /**