diff --git a/apps/web/src/composerDraftStore.test.ts b/apps/web/src/composerDraftStore.test.ts
index 246dfbf4c01e698e57b2805a7c15fa323d44620e..80ec5c39aac8101100382dc3535f701797a5b6da 100644
--- a/apps/web/src/composerDraftStore.test.ts
+++ b/apps/web/src/composerDraftStore.test.ts
@@ -242,3 +242,23 @@ describe("composerDraftStore project draft thread mapping", () => {
     });
   });
 });
+
+describe("composerDraftStore setModel", () => {
+  const threadId = ThreadId.makeUnsafe("thread-model");
+
+  beforeEach(() => {
+    useComposerDraftStore.setState({
+      draftsByThreadId: {},
+      draftThreadsByThreadId: {},
+      projectDraftThreadIdByProjectId: {},
+    });
+  });
+
+  it("keeps explicit DEFAULT_MODEL overrides instead of coercing to null", () => {
+    const store = useComposerDraftStore.getState();
+
+    store.setModel(threadId, "gpt-5.3-codex");
+
+    expect(useComposerDraftStore.getState().draftsByThreadId[threadId]?.model).toBe("gpt-5.3-codex");
+  });
+});
diff --git a/apps/web/src/composerDraftStore.ts b/apps/web/src/composerDraftStore.ts
index c132aa07a84c91bed75c9f3bab3d838936a4c7c0..675aa7402b78665ac7e8addbaf67b8cb0fcee7f5 100644
--- a/apps/web/src/composerDraftStore.ts
+++ b/apps/web/src/composerDraftStore.ts
@@ -1,5 +1,4 @@
 import {
-  DEFAULT_MODEL,
   DEFAULT_REASONING,
   ProjectId,
   REASONING_OPTIONS,
@@ -671,11 +670,7 @@ export const useComposerDraftStore = create<ComposerDraftStoreState>()(
         if (threadId.length === 0) {
           return;
         }
-        const normalizedModelCandidate = normalizeModelSlug(model);
-        const normalizedModel =
-          normalizedModelCandidate && normalizedModelCandidate !== DEFAULT_MODEL
-            ? normalizedModelCandidate
-            : null;
+        const normalizedModel = normalizeModelSlug(model) ?? null;
         set((state) => {
           const existing = state.draftsByThreadId[threadId];
           if (!existing && normalizedModel === null) {