diff --git a/web/src/components/NewSession/index.test.tsx b/web/src/components/NewSession/index.test.tsx
index 699a8388..b91ef77f 100644
--- a/web/src/components/NewSession/index.test.tsx
+++ b/web/src/components/NewSession/index.test.tsx
@@ -1,5 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
-import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react'
 import type { ApiClient } from '@/api/client'
 import type { Machine } from '@/types/api'
 import { saveNewSessionFormDraft } from './newSessionFormDraft'
@@ -156,10 +156,17 @@ vi.mock('./ModelSelector', () => ({
     ModelSelector: (props: {
         model: string
         options?: Array<{ value: string; label: string }>
+        isDisabled: boolean
+        isLoading?: boolean
         onModelChange: (model: string) => void
     }) => (
         <>
-            <button type="button" data-testid="model" onClick={() => props.onModelChange('gpt-5.6-terra')}>
+            <button
+                type="button"
+                data-testid="model"
+                disabled={props.isDisabled || props.isLoading}
+                onClick={() => props.onModelChange('gpt-5.6-terra')}
+            >
                 {props.model}
             </button>
             <div data-testid="model-options">{props.options?.map((option) => option.label).join(',')}</div>
@@ -309,6 +316,52 @@ describe('NewSession launch preferences', () => {
         })
     })
 
+    it('blocks model changes and creation until custom Claude models load', async () => {
+        savePreferredAgent('claude')
+        savePreferredLaunchSettings('machine-1', 'claude', {
+            model: 'deepseek-v4-flash[1m]',
+            cursorSelectedBase: 'auto',
+            effort: 'high',
+            modelReasoningEffort: 'default'
+        })
+        let resolveModels!: (value: { models: string[] }) => void
+        const claudeApi = {
+            getClaudeCustomModels: vi.fn().mockReturnValue(new Promise((resolve) => {
+                resolveModels = resolve
+            }))
+        } as unknown as ApiClient
+
+        render(
+            <NewSession
+                api={claudeApi}
+                machines={[machine]}
+                initialMachineId="machine-1"
+                initialDirectory="C:\\repo"
+                onSuccess={mocks.onSuccess}
+                onCancel={() => {}}
+            />
+        )
+
+        const model = screen.getByTestId('model')
+        const create = screen.getByTestId('create')
+        expect(model).toBeDisabled()
+        expect(create).toBeDisabled()
+        fireEvent.click(model)
+        fireEvent.click(create)
+        expect(model).toHaveTextContent('auto')
+        expect(mocks.spawnSession).not.toHaveBeenCalled()
+
+        await act(async () => {
+            resolveModels({ models: ['deepseek-v4-flash[1m]'] })
+        })
+
+        await waitFor(() => {
+            expect(model).toHaveTextContent('deepseek-v4-flash[1m]')
+            expect(model).toBeEnabled()
+            expect(create).toBeEnabled()
+        })
+    })
+
     it.each([
         ['model', 'gpt-5.6-sol', 'default'],
         ['reasoning effort', 'auto', 'xhigh']
diff --git a/web/src/components/NewSession/index.tsx b/web/src/components/NewSession/index.tsx
index ecee9998..b32ba264 100644
--- a/web/src/components/NewSession/index.tsx
+++ b/web/src/components/NewSession/index.tsx
@@ -308,7 +308,8 @@ export function NewSession(props: {
         () => agent === 'claude' ? claudeModelOptions.map((option) => option.value) : null,
         [agent, claudeModelOptions]
     )
-    const preferredModelCatalogReady = agent !== 'claude' || claudeModelsLoaded
+    const claudeModelsLoading = agent === 'claude' && !claudeModelsLoaded
+    const preferredModelCatalogReady = !claudeModelsLoading
     const runnerSpawnError = useMemo(
         () => formatRunnerSpawnError(selectedMachine),
         [selectedMachine]
@@ -1342,7 +1343,8 @@ export function NewSession(props: {
     }
 
     const isLaunchPreferenceValidationPending =
-        (agent === 'codex'
+        claudeModelsLoading
+        || (agent === 'codex'
             && (model !== 'auto' || modelReasoningEffort !== 'default')
             && codexModelsState.isLoading)
         || (agent === 'agy'
@@ -1522,7 +1524,8 @@ export function NewSession(props: {
                             || (agent === 'grok' && Boolean(grokModelsState.error))
                             || (agent === 'copilot' && Boolean(copilotModelsState.error))
                         }
-                        isLoading={(agent === 'codex' && codexModelsState.isLoading)
+                        isLoading={claudeModelsLoading
+                            || (agent === 'codex' && codexModelsState.isLoading)
                             || (agent === 'grok' && grokModelsState.isLoading)
                             || (agent === 'copilot' && copilotModelsState.isLoading)}
                         error={agent === 'codex' && codexModelsState.error