diff --git a/cli/src/runner/buildCliArgs.test.ts b/cli/src/runner/buildCliArgs.test.ts
index 612e2d1d6..e1bcc679f 100644
--- a/cli/src/runner/buildCliArgs.test.ts
+++ b/cli/src/runner/buildCliArgs.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import { buildCliArgs } from './run'
+import { buildCliArgs, shouldSetClaudeHaikuModelEnv } from './run'
 
 describe('buildCliArgs', () => {
     it('adds --permission-mode for valid permission mode', () => {
@@ -61,4 +61,14 @@ describe('buildCliArgs', () => {
             expect(args).toContain(mode)
         }
     })
+
+    it('detects custom Claude models for Haiku env override', () => {
+        expect(shouldSetClaudeHaikuModelEnv('claude', 'claude-3-5-haiku-latest')).toBe(true)
+        expect(shouldSetClaudeHaikuModelEnv('claude', 'opus')).toBe(false)
+        expect(shouldSetClaudeHaikuModelEnv('claude', 'opus[1m]')).toBe(false)
+        expect(shouldSetClaudeHaikuModelEnv('claude', 'sonnet')).toBe(false)
+        expect(shouldSetClaudeHaikuModelEnv('claude', 'sonnet[1m]')).toBe(false)
+        expect(shouldSetClaudeHaikuModelEnv('codex', 'claude-3-5-haiku-latest')).toBe(false)
+        expect(shouldSetClaudeHaikuModelEnv('claude')).toBe(false)
+    })
 })
diff --git a/cli/src/runner/run.ts b/cli/src/runner/run.ts
index 2e6361101..d0cc10035 100644
--- a/cli/src/runner/run.ts
+++ b/cli/src/runner/run.ts
@@ -25,6 +25,16 @@ import { buildMachineMetadata } from '@/agent/sessionFactory';
 import { resolveWorkspaceRoot } from '@/utils/workspaceRoot';
 import { hashRunnerCliApiToken } from './runnerIdentity';
 
+const CLAUDE_BUILT_IN_MODEL_ALIASES = new Set(['opus', 'opus[1m]', 'sonnet', 'sonnet[1m]']);
+
+export function shouldSetClaudeHaikuModelEnv(agent: string, model?: string): boolean {
+  if (agent !== 'claude') {
+    return false;
+  }
+  const normalizedModel = model?.trim();
+  return Boolean(normalizedModel && !CLAUDE_BUILT_IN_MODEL_ALIASES.has(normalizedModel));
+}
+
 export async function startRunner(options: { workspaceRoot?: string } = {}): Promise<void> {
   // We don't have cleanup function at the time of server construction
   // Control flow is:
@@ -378,6 +388,13 @@ export async function startRunner(options: { workspaceRoot?: string } = {}): Pro
           };
         }
 
+        if (shouldSetClaudeHaikuModelEnv(agent, options.model) && options.model) {
+          extraEnv = {
+            ...extraEnv,
+            ANTHROPIC_DEFAULT_HAIKU_MODEL: options.model
+          };
+        }
+
         const args = buildCliArgs(agent, options, yolo);
 
         // sessionId reserved for future use
diff --git a/web/src/components/NewSession/ModelSelector.tsx b/web/src/components/NewSession/ModelSelector.tsx
index 7977c55a5..32483a96a 100644
--- a/web/src/components/NewSession/ModelSelector.tsx
+++ b/web/src/components/NewSession/ModelSelector.tsx
@@ -5,11 +5,13 @@ import { useTranslation } from '@/lib/use-translation'
 export function ModelSelector(props: {
     agent: AgentType
     model: string
+    customModel: string
     options?: Array<{ value: string; label: string }>
     isDisabled: boolean
     isLoading?: boolean
     error?: string | null
     onModelChange: (value: string) => void
+    onCustomModelChange: (value: string) => void
 }) {
     const { t } = useTranslation()
     const options = props.options ?? MODEL_OPTIONS[props.agent]
@@ -40,6 +42,16 @@ export function ModelSelector(props: {
                     {props.error}
                 </div>
             ) : null}
+            {props.agent === 'claude' && props.model === 'custom' ? (
+                <input
+                    type="text"
+                    value={props.customModel}
+                    onChange={(e) => props.onCustomModelChange(e.target.value)}
+                    disabled={props.isDisabled || props.isLoading}
+                    placeholder={t('newSession.model.custom.placeholder')}
+                    className="w-full px-3 py-2 text-sm rounded-lg border border-[var(--app-divider)] bg-[var(--app-bg)] text-[var(--app-text)] focus:outline-none focus:ring-2 focus:ring-[var(--app-link)] disabled:opacity-50"
+                />
+            ) : null}
         </div>
     )
 }
diff --git a/web/src/components/NewSession/index.tsx b/web/src/components/NewSession/index.tsx
index 721596b8d..756218372 100644
--- a/web/src/components/NewSession/index.tsx
+++ b/web/src/components/NewSession/index.tsx
@@ -51,6 +51,7 @@ export function NewSession(props: {
     const [isDirectoryFocused, setIsDirectoryFocused] = useState(false)
     const [agent, setAgent] = useState<AgentType>(loadPreferredAgent)
     const [model, setModel] = useState('auto')
+    const [customModel, setCustomModel] = useState('')
     const [effort, setEffort] = useState<ClaudeEffort>('auto')
     const [modelReasoningEffort, setModelReasoningEffort] = useState<CodexReasoningEffort>('default')
     const [yoloMode, setYoloMode] = useState(loadPreferredYoloMode)
@@ -68,6 +69,7 @@ export function NewSession(props: {
 
     useEffect(() => {
         setModel('auto')
+        setCustomModel('')
         setEffort('auto')
     }, [agent])
 
@@ -277,7 +279,16 @@ export function NewSession(props: {
                 return
             }
 
-            const resolvedModel = model !== 'auto' && agent !== 'opencode' ? model : undefined
+            const trimmedCustomModel = customModel.trim()
+            if (agent === 'claude' && model === 'custom' && !trimmedCustomModel) {
+                setError(t('newSession.model.custom.required'))
+                return
+            }
+            const resolvedModel = agent === 'claude' && model === 'custom'
+                ? trimmedCustomModel
+                : model !== 'auto' && agent !== 'opencode'
+                    ? model
+                    : undefined
             const resolvedEffort = agent === 'claude' && effort !== 'auto' ? effort : undefined
             const resolvedModelReasoningEffort = agent === 'codex' && modelReasoningEffort !== 'default'
                 ? modelReasoningEffort
@@ -358,6 +369,7 @@ export function NewSession(props: {
             <ModelSelector
                 agent={agent}
                 model={model}
+                customModel={customModel}
                 options={agent === 'codex' ? codexModelOptions : undefined}
                 isDisabled={isFormDisabled || (agent === 'codex' && Boolean(codexModelsState.error))}
                 isLoading={agent === 'codex' && codexModelsState.isLoading}
@@ -365,6 +377,7 @@ export function NewSession(props: {
                     ? `${t('newSession.model.loadFailed')}: ${codexModelsState.error}`
                     : null}
                 onModelChange={setModel}
+                onCustomModelChange={setCustomModel}
             />
             <ClaudeEffortSelector
                 agent={agent}
diff --git a/web/src/components/NewSession/types.test.ts b/web/src/components/NewSession/types.test.ts
index 08591db02..b044d6de9 100644
--- a/web/src/components/NewSession/types.test.ts
+++ b/web/src/components/NewSession/types.test.ts
@@ -10,6 +10,7 @@ describe('Claude model options', () => {
             { value: 'opus[1m]', label: 'Opus 1M' },
             { value: 'sonnet', label: 'Sonnet' },
             { value: 'sonnet[1m]', label: 'Sonnet 1M' },
+            { value: 'custom', label: 'Custom' },
         ])
     })
 
diff --git a/web/src/components/NewSession/types.ts b/web/src/components/NewSession/types.ts
index a950a6ff0..6e15e9c8f 100644
--- a/web/src/components/NewSession/types.ts
+++ b/web/src/components/NewSession/types.ts
@@ -12,6 +12,7 @@ export const MODEL_OPTIONS: Record<AgentType, { value: string; label: string }[]
         { value: 'opus[1m]', label: 'Opus 1M' },
         { value: 'sonnet', label: 'Sonnet' },
         { value: 'sonnet[1m]', label: 'Sonnet 1M' },
+        { value: 'custom', label: 'Custom' },
     ],
     codex: [
         { value: 'auto', label: 'Default' },
diff --git a/web/src/lib/locales/en.ts b/web/src/lib/locales/en.ts
index ddd86b20b..bd43ef412 100644
--- a/web/src/lib/locales/en.ts
+++ b/web/src/lib/locales/en.ts
@@ -116,6 +116,8 @@ export default {
   'newSession.model': 'Model',
   'newSession.effort': 'Effort',
   'newSession.model.optional': 'optional',
+  'newSession.model.custom.placeholder': 'Enter Claude model name',
+  'newSession.model.custom.required': 'Custom model is required',
   'newSession.model.loadFailed': 'Failed to load Codex models',
   'newSession.reasoningEffort': 'Reasoning effort',
   'newSession.yolo': 'YOLO mode',
diff --git a/web/src/lib/locales/zh-CN.ts b/web/src/lib/locales/zh-CN.ts
index d9bd35bf5..c387bbc36 100644
--- a/web/src/lib/locales/zh-CN.ts
+++ b/web/src/lib/locales/zh-CN.ts
@@ -118,6 +118,8 @@ export default {
   'newSession.model': '模型',
   'newSession.effort': '思考强度',
   'newSession.model.optional': '可选',
+  'newSession.model.custom.placeholder': '输入自定义模型名称',
+  'newSession.model.custom.required': '请输入自定义模型名称',
   'newSession.model.loadFailed': '加载 Codex 模型失败',
   'newSession.reasoningEffort': '推理强度',
   'newSession.yolo': 'YOLO 模式',