diff --git a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts
index 7fece9817ce01..a65a6fb3306c7 100644
--- a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts
+++ b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts
@@ -850,6 +850,84 @@ describe("ClaudeAdapterV2 Auto-accept edits", () => {
   );
 });
 
+describe("ClaudeAdapterV2 custom model names", () => {
+  it.effect("sends a custom model that shares a built-in alias under its own name", () =>
+    Effect.scoped(
+      Effect.gen(function* () {
+        const fileSystem = yield* FileSystem.FileSystem;
+        const opened: Array<ClaudeAdapterV2.ClaudeAgentSdkQueryOptions> = [];
+        const adapter = yield* ClaudeAdapterV2.makeClaudeAdapterV2({
+          instanceId: ClaudeAdapterV2.CLAUDE_DEFAULT_INSTANCE_ID,
+          settings: CUSTOM_MODEL_CLAUDE_SETTINGS,
+          environment: {},
+          attachmentsDir: yield* fileSystem.makeTempDirectoryScoped({
+            prefix: "t3-claude-custom-",
+          }),
+          fileSystem,
+          path: yield* Path.Path,
+          crypto: yield* Crypto.Crypto,
+          idAllocator: yield* IdAllocator.IdAllocatorV2,
+          queryRunner: {
+            allocateSessionId: Effect.succeed("native-thread-claude-custom"),
+            open: (input) =>
+              Effect.sync(() => {
+                opened.push(input.options);
+                return {
+                  messages: Stream.never,
+                  offer: () => Effect.void,
+                  setModel: () => Effect.void,
+                  applyFlagSettings: () => Effect.void,
+                  setPermissionMode: () => Effect.void,
+                  backgroundTasks: () => Effect.succeed(false),
+                  stopTask: () => Effect.void,
+                  interrupt: Effect.void,
+                  close: Effect.void,
+                };
+              }),
+            forkSession: () => Effect.die("unused"),
+            subagentLaunchToolUseId: () => Effect.succeed(null),
+            assertComplete: Effect.void,
+          },
+        });
+        // "opus" is a built-in alias, and a proxy may serve its own model of that name.
+        const modelSelection = { ...CLAUDE_TEST_MODEL_SELECTION, model: "opus", options: [] };
+        const threadId = ThreadId.make("thread-claude-custom");
+        const runtime = yield* adapter.openSession({
+          threadId,
+          providerSessionId: ProviderSessionId.make("provider-session-claude-custom"),
+          modelSelection,
+          runtimePolicy: CLAUDE_TEST_RUNTIME_POLICY,
+        });
+        const providerThread = yield* runtime.ensureThread({
+          threadId,
+          modelSelection,
+          runtimePolicy: CLAUDE_TEST_RUNTIME_POLICY,
+        });
+        yield* runtime
+          .startTurn(
+            makeClaudeTestTurnInput({
+              threadId,
+              providerThread,
+              now: yield* DateTime.now,
+              attemptId: RunAttemptId.make("attempt-claude-custom"),
+              text: "Hello",
+              attachments: [],
+              modelSelection,
+            }),
+          )
+          .pipe(Effect.exit);
+
+        assert.lengthOf(opened, 1);
+        assert.equal(opened[0]!.model, "opus");
+      }).pipe(
+        Effect.provide(
+          Layer.mergeAll(IdAllocator.layer, McpProviderSessions.layer, NodeServices.layer),
+        ),
+      ),
+    ),
+  );
+});
+
 describe("ClaudeAdapterV2 append-system-prompt-file launch argument", () => {
   const startTurnWithLaunchArgs = Effect.fnUntraced(function* (launchArgs: string, cwd: string) {
     const fileSystem = yield* FileSystem.FileSystem;
diff --git a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
index 94ccc16dda54c..e45c499ee1cfb 100644
--- a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
+++ b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
@@ -1424,8 +1424,9 @@ export function makeClaudeQueryOptions(input: {
   readonly appendSystemPromptFileText?: string;
   // Flag settings, because a user's settings.json env beats the process env in Claude Code.
   readonly toolSearchOverride?: "true";
+  readonly modelCatalog?: ClaudeModelCatalog;
 }): ClaudeAgentSdkQueryOptions {
-  const compiledSelection = compileClaudeModelSelection(input.modelSelection);
+  const compiledSelection = compileClaudeModelSelection(input.modelSelection, input.modelCatalog);
   const {
     "permission-mode": launchArgPermissionMode,
     "dangerously-skip-permissions": launchArgSkipPermissions,
@@ -4242,7 +4243,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
   const spawner = yield* ChildProcessSpawner.ChildProcessSpawner;
   const serverSettings = yield* Effect.serviceOption(ServerSettings.ServerSettingsService);
   const { attachmentsDir, fileSystem, path, crypto, idAllocator, queryRunner } = adapterOptions;
-  const subagentModelCatalog = scopeClaudeModelCatalog(
+  const scopedModelCatalog = scopeClaudeModelCatalog(
     BUNDLED_CLAUDE_MODEL_CATALOG,
     adapterOptions.settings.customModels,
   );
@@ -6081,7 +6082,8 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             existingSubagent === undefined
               ? (input.effort ??
                 input.owner?.effort ??
-                compileClaudeModelSelection(input.context.input.modelSelection).effort)
+                compileClaudeModelSelection(input.context.input.modelSelection, scopedModelCatalog)
+                  .effort)
               : existingSubagent.effort;
           const model = input.model ?? priorTask?.model ?? null;
           const task = {
@@ -6119,7 +6121,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             ...(existingSubagent === undefined || existingSubagent.task.modelSelection !== undefined
               ? {
                   modelSelection: claudeSubagentModelSelection(
-                    subagentModelCatalog,
+                    scopedModelCatalog,
                     input.context.input.modelSelection.instanceId,
                     model || input.context.input.modelSelection.model,
                     effort,
@@ -8424,7 +8426,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             const model =
               snapshotModel.length === 0 || snapshotModel === "<synthetic>"
                 ? undefined
-                : canonicalClaudeSubagentModel(subagentModelCatalog, snapshotModel);
+                : canonicalClaudeSubagentModel(scopedModelCatalog, snapshotModel);
             if (parentToolUseId !== null && model !== undefined) {
               const subagent = yield* resolveSubagentByToolUseId(context, parentToolUseId);
               if (subagent === undefined) {
@@ -8708,7 +8710,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             const nativeToolInput = claudeNativeToolInputFromUnknown(toolUse.input);
             if (toolUse.name === "Agent") {
               rememberClaudeSubagentLaunch(
-                subagentModelCatalog,
+                scopedModelCatalog,
                 context,
                 pendingSubagentLaunchesByToolUseId,
                 toolUse.id,
@@ -9280,7 +9282,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
           const heldForEcho = context.heldRootFrames.length > 0;
           if (toolName === "Agent") {
             rememberClaudeSubagentLaunch(
-              subagentModelCatalog,
+              scopedModelCatalog,
               context,
               pendingSubagentLaunchesByToolUseId,
               nativeRequestId,
@@ -9631,7 +9633,10 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
               : { allowedTools: queryPolicy.allowedTools }),
           });
           const queryPolicyKey = claudeEffectiveQueryPolicyKey(queryPolicy, mcpOverrides);
-          const compiledSelection = compileClaudeModelSelection(turnInput.modelSelection);
+          const compiledSelection = compileClaudeModelSelection(
+            turnInput.modelSelection,
+            scopedModelCatalog,
+          );
           const resumeSessionAt = yield* getNativeConversationHeadId(turnInput.providerThread);
           const existing = yield* Ref.get(queryContext);
           // Continuations drain existing output without prompting; retain the live process regardless of selection.
@@ -9759,6 +9764,7 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             supportedDialogKinds: ["resume_return"],
             ...(appendSystemPromptFileText === undefined ? {} : { appendSystemPromptFileText }),
             ...(toolSearchOverride === undefined ? {} : { toolSearchOverride }),
+            modelCatalog: scopedModelCatalog,
           });
           const querySession = yield* queryRunner
             .open({
@@ -9927,7 +9933,8 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
                 : yield* makeClaudeUserMessageWithAttachments({
                     text: applyClaudePromptEffortPrefix(
                       turnInput.message.text,
-                      compileClaudeModelSelection(turnInput.modelSelection).promptEffort,
+                      compileClaudeModelSelection(turnInput.modelSelection, scopedModelCatalog)
+                        .promptEffort,
                     ),
                     attachments: turnInput.message.attachments,
                     attachmentsDir,
@@ -10380,7 +10387,8 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
             const userMessage = yield* makeClaudeUserMessageWithAttachments({
               text: applyClaudePromptEffortPrefix(
                 turnInput.message.text,
-                compileClaudeModelSelection(currentTurn.input.modelSelection).promptEffort,
+                compileClaudeModelSelection(currentTurn.input.modelSelection, scopedModelCatalog)
+                  .promptEffort,
               ),
               attachments: turnInput.message.attachments,
               priority: "now",