diff --git a/coderd/chats_test.go b/coderd/chats_test.go
index 139b947aa8..21d734d818 100644
--- a/coderd/chats_test.go
+++ b/coderd/chats_test.go
@@ -3479,58 +3479,105 @@ func TestGetChatFile(t *testing.T) {
 	})
 }
 
+type chatCostTestFixture struct {
+	Client        *codersdk.Client
+	DB            database.Store
+	ModelConfigID uuid.UUID
+	ChatID        uuid.UUID
+}
+
+func seedChatCostFixture(t *testing.T) chatCostTestFixture {
+	t.Helper()
+
+	ctx := testutil.Context(t, testutil.WaitLong)
+	client, db := newChatClientWithDatabase(t)
+	firstUser := coderdtest.CreateFirstUser(t, client)
+	modelConfig := createChatModelConfig(t, client)
+
+	chat, err := db.InsertChat(dbauthz.AsSystemRestricted(ctx), database.InsertChatParams{
+		OwnerID:           firstUser.UserID,
+		LastModelConfigID: modelConfig.ID,
+		Title:             "test chat",
+	})
+	require.NoError(t, err)
+
+	for i := 0; i < 2; i++ {
+		_, err = db.InsertChatMessage(dbauthz.AsSystemRestricted(ctx), database.InsertChatMessageParams{
+			ChatID:          chat.ID,
+			ModelConfigID:   uuid.NullUUID{UUID: modelConfig.ID, Valid: true},
+			Role:            "assistant",
+			Visibility:      database.ChatMessageVisibilityBoth,
+			InputTokens:     sql.NullInt64{Int64: 100, Valid: true},
+			OutputTokens:    sql.NullInt64{Int64: 50, Valid: true},
+			TotalCostMicros: sql.NullInt64{Int64: 500, Valid: true},
+		})
+		require.NoError(t, err)
+	}
+
+	return chatCostTestFixture{
+		Client:        client,
+		DB:            db,
+		ModelConfigID: modelConfig.ID,
+		ChatID:        chat.ID,
+	}
+}
+
+func assertChatCostSummary(t *testing.T, summary codersdk.ChatCostSummary, modelConfigID, chatID uuid.UUID) {
+	t.Helper()
+
+	require.Equal(t, int64(1000), summary.TotalCostMicros)
+	require.Equal(t, int64(2), summary.PricedMessageCount)
+	require.Equal(t, int64(0), summary.UnpricedMessageCount)
+	require.Equal(t, int64(200), summary.TotalInputTokens)
+	require.Equal(t, int64(100), summary.TotalOutputTokens)
+
+	require.Len(t, summary.ByModel, 1)
+	require.Equal(t, modelConfigID, summary.ByModel[0].ModelConfigID)
+	require.Equal(t, int64(1000), summary.ByModel[0].TotalCostMicros)
+	require.Equal(t, int64(2), summary.ByModel[0].MessageCount)
+
+	require.Len(t, summary.ByChat, 1)
+	require.Equal(t, chatID, summary.ByChat[0].RootChatID)
+	require.Equal(t, int64(1000), summary.ByChat[0].TotalCostMicros)
+	require.Equal(t, int64(2), summary.ByChat[0].MessageCount)
+}
+
 func TestChatCostSummary(t *testing.T) {
 	t.Parallel()
 
 	t.Run("BasicSummary", func(t *testing.T) {
 		t.Parallel()
 
+		f := seedChatCostFixture(t)
 		ctx := testutil.Context(t, testutil.WaitLong)
-		client, db := newChatClientWithDatabase(t)
-		firstUser := coderdtest.CreateFirstUser(t, client)
-		modelConfig := createChatModelConfig(t, client)
 
-		chat, err := db.InsertChat(dbauthz.AsSystemRestricted(ctx), database.InsertChatParams{
-			OwnerID:           firstUser.UserID,
-			LastModelConfigID: modelConfig.ID,
-			Title:             "test chat",
-		})
+		summary, err := f.Client.GetChatCostSummary(ctx, "me", codersdk.ChatCostSummaryOptions{})
 		require.NoError(t, err)
-
-		for i := 0; i < 2; i++ {
-			_, err = db.InsertChatMessage(dbauthz.AsSystemRestricted(ctx), database.InsertChatMessageParams{
-				ChatID:          chat.ID,
-				ModelConfigID:   uuid.NullUUID{UUID: modelConfig.ID, Valid: true},
-				Role:            "assistant",
-				Visibility:      database.ChatMessageVisibilityBoth,
-				InputTokens:     sql.NullInt64{Int64: 100, Valid: true},
-				OutputTokens:    sql.NullInt64{Int64: 50, Valid: true},
-				TotalCostMicros: sql.NullInt64{Int64: 500, Valid: true},
-			})
-			require.NoError(t, err)
-		}
-
-		summary, err := client.GetChatCostSummary(ctx, "me", codersdk.ChatCostSummaryOptions{})
-		require.NoError(t, err)
-
-		require.Equal(t, int64(1000), summary.TotalCostMicros)
-		require.Equal(t, int64(2), summary.PricedMessageCount)
-		require.Equal(t, int64(0), summary.UnpricedMessageCount)
-		require.Equal(t, int64(200), summary.TotalInputTokens)
-		require.Equal(t, int64(100), summary.TotalOutputTokens)
-
-		require.Len(t, summary.ByModel, 1)
-		require.Equal(t, modelConfig.ID, summary.ByModel[0].ModelConfigID)
-		require.Equal(t, int64(1000), summary.ByModel[0].TotalCostMicros)
-		require.Equal(t, int64(2), summary.ByModel[0].MessageCount)
-
-		require.Len(t, summary.ByChat, 1)
-		require.Equal(t, chat.ID, summary.ByChat[0].RootChatID)
-		require.Equal(t, int64(1000), summary.ByChat[0].TotalCostMicros)
-		require.Equal(t, int64(2), summary.ByChat[0].MessageCount)
+		assertChatCostSummary(t, summary, f.ModelConfigID, f.ChatID)
 	})
 }
 
+func TestChatCostSummary_AfterModelDeletion(t *testing.T) {
+	t.Parallel()
+
+	f := seedChatCostFixture(t)
+	ctx := testutil.Context(t, testutil.WaitLong)
+
+	// Baseline: costs are correct before deletion.
+	summary, err := f.Client.GetChatCostSummary(ctx, "me", codersdk.ChatCostSummaryOptions{})
+	require.NoError(t, err)
+	assertChatCostSummary(t, summary, f.ModelConfigID, f.ChatID)
+
+	// Soft-delete the model config.
+	err = f.Client.DeleteChatModelConfig(ctx, f.ModelConfigID)
+	require.NoError(t, err)
+
+	// Costs must survive the deletion unchanged.
+	summary, err = f.Client.GetChatCostSummary(ctx, "me", codersdk.ChatCostSummaryOptions{})
+	require.NoError(t, err)
+	assertChatCostSummary(t, summary, f.ModelConfigID, f.ChatID)
+}
+
 func TestChatCostSummary_AdminDrilldown(t *testing.T) {
 	t.Parallel()