fix(agent-teams): inherit the lead model instead of hardcoded Opus

Unconfigured teammates were spawned as claude-opus-4-8, so mapped
third-party providers such as cc-switch DeepSeek billed the expensive
fallback. Agent page aliases now resolve through the provider mapping.

src/components/Settings/Config.tsx

@@ -44,7 +44,6 @@ import type { LocalJSXCommandContext, CommandResultDisplay } from '../../command
 import { getFeatureValue_CACHED_MAY_BE_STALE } from '../../services/analytics/growthbook.js';
 import { isAgentSwarmsEnabled } from '../../utils/agentSwarmsEnabled.js';
 import { getCliTeammateModeOverride, clearCliTeammateModeOverride } from '../../utils/swarm/backends/teammateModeSnapshot.js';
-import { getHardcodedTeammateModelFallback } from '../../utils/swarm/teammateModel.js';
 import { useSearchInput } from '../../hooks/useSearchInput.js';
 import { useTerminalSize } from '../../hooks/useTerminalSize.js';
 import { clearFastModeCooldown, FAST_MODE_MODEL_DISPLAY, isFastModeAvailable, isFastModeEnabled, getFastModeModel, isFastModeSupportedByModel } from '../../utils/fastMode.js';
@@ -1540,8 +1539,8 @@ export function Config({
         setShowSubmenu(null);
         setTabsHidden(false);
         // First-open-then-Enter from unset: picker highlights "Default"
-        // (initial=null) and confirming would write null, silently
-        // switching Opus-fallback → follow-leader. Treat as no-op.
+        // (initial=null) and confirming would write null. Unset already
+        // follows the leader, so treat as no-op.
         if (globalConfig.teammateDefaultModel === undefined && model_1 === null) {
           return;
         }
@@ -1789,10 +1788,7 @@ export function Config({
     </Box>;
 }
 function teammateModelDisplayString(value: string | null | undefined): string {
-  if (value === undefined) {
-    return modelDisplayString(getHardcodedTeammateModelFallback());
-  }
-  if (value === null) return "Default (leader's model)";
+  if (value === undefined || value === null) return "Default (leader's model)";
   return modelDisplayString(value);
 }
 const THEME_LABELS: Record<string, string> = {

src/tools/shared/spawnMultiAgent.callsite.test.ts

@@ -1,6 +1,7 @@
 import { afterAll, beforeEach, describe, expect, mock, test } from 'bun:test'
 import type { AppState } from '../../state/AppState.js'
 import type { ToolUseContext } from '../../Tool.js'
+import { parseUserSpecifiedModel } from '../../utils/model/model.js'
 import type {
   CustomAgentDefinition,
   PluginAgentDefinition,
@@ -213,7 +214,7 @@ describe('Agent Teams custom Agent runtime call sites', () => {
       makeContext(pluginAgent),
     )
 
-    expect(result.data.model).toBe('opus')
+    expect(result.data.model).toBe(parseUserSpecifiedModel('opus'))
     const runnerConfig = startInProcessTeammateMock.mock.calls[0]?.[0] as {
       agentDefinition?: PluginAgentDefinition
     }

src/tools/shared/spawnMultiAgent.test.ts

@@ -1,11 +1,13 @@
 import { afterEach, describe, expect, test } from 'bun:test'
 import { getGlobalConfig, saveGlobalConfig } from '../../utils/config.js'
+import { parseUserSpecifiedModel } from '../../utils/model/model.js'
 import {
   buildTeammateRuntimeCliFlags,
   resolveTeammateModel,
 } from './spawnMultiAgent.js'
 
 const originalSubagentModel = process.env.CLAUDE_CODE_SUBAGENT_MODEL
+const originalOpusModel = process.env.ANTHROPIC_DEFAULT_OPUS_MODEL
 const originalTeammateDefaultModel = getGlobalConfig().teammateDefaultModel
 
 afterEach(() => {
@@ -14,6 +16,11 @@ afterEach(() => {
   } else {
     process.env.CLAUDE_CODE_SUBAGENT_MODEL = originalSubagentModel
   }
+  if (originalOpusModel === undefined) {
+    delete process.env.ANTHROPIC_DEFAULT_OPUS_MODEL
+  } else {
+    process.env.ANTHROPIC_DEFAULT_OPUS_MODEL = originalOpusModel
+  }
   saveGlobalConfig(current => ({
     ...current,
     teammateDefaultModel: originalTeammateDefaultModel,
@@ -75,7 +82,7 @@ describe('buildTeammateRuntimeCliFlags', () => {
 
     expect(
       resolveTeammateModel('haiku', 'claude-sonnet-4-6', 'gpt-5.6-luna'),
-    ).toBe('haiku')
+    ).toBe(parseUserSpecifiedModel('haiku'))
   })
 
   test('treats a global inherit override as normal teammate resolution', () => {
@@ -84,7 +91,9 @@ describe('buildTeammateRuntimeCliFlags', () => {
       ...current,
       teammateDefaultModel: null,
     }))
-    expect(resolveTeammateModel('haiku', 'claude-sonnet-4-6')).toBe('haiku')
+    expect(resolveTeammateModel('haiku', 'claude-sonnet-4-6')).toBe(
+      parseUserSpecifiedModel('haiku'),
+    )
     expect(resolveTeammateModel(undefined, 'claude-sonnet-4-6')).toBe(
       'claude-sonnet-4-6',
     )
@@ -113,6 +122,41 @@ describe('buildTeammateRuntimeCliFlags', () => {
     ).toBe('gpt-5.6-luna')
   })
 
+  test('unset teammateDefaultModel follows the leader instead of a hardcoded Opus ID', () => {
+    delete process.env.CLAUDE_CODE_SUBAGENT_MODEL
+    saveGlobalConfig(current => {
+      const next = { ...current }
+      delete next.teammateDefaultModel
+      return next
+    })
+
+    expect(
+      resolveTeammateModel(
+        undefined,
+        'deepseek-flash',
+        undefined,
+        false,
+      ),
+    ).toBe('deepseek-flash')
+  })
+
+  test('an Agent page opus pin resolves through the provider mapping', () => {
+    delete process.env.CLAUDE_CODE_SUBAGENT_MODEL
+    process.env.ANTHROPIC_DEFAULT_OPUS_MODEL = 'deepseek-flash'
+    saveGlobalConfig(current => {
+      const next = { ...current }
+      delete next.teammateDefaultModel
+      return next
+    })
+
+    expect(
+      resolveTeammateModel(undefined, 'deepseek-flash', 'opus', true),
+    ).toBe('deepseek-flash')
+    expect(
+      resolveTeammateModel(undefined, 'deepseek-flash', 'inherit', true),
+    ).toBe('deepseek-flash')
+  })
+
   test('selected Agents inherit the leader when model is omitted or inherit', () => {
     delete process.env.CLAUDE_CODE_SUBAGENT_MODEL
     saveGlobalConfig(current => ({

src/tools/shared/spawnMultiAgent.ts

@@ -79,14 +79,13 @@ import {
 
 function getDefaultTeammateModel(leaderModel: string | null): string {
   const configured = getGlobalConfig().teammateDefaultModel
-  if (configured === null) {
-    // User picked "Default" in the /config picker — follow the leader.
-    return leaderModel ?? getHardcodedTeammateModelFallback()
-  }
-  if (configured !== undefined) {
+  if (typeof configured === 'string' && configured.trim()) {
     return parseUserSpecifiedModel(configured)
   }
-  return getHardcodedTeammateModelFallback()
+  // Unset (`undefined`) and /config "Default" (`null`) both follow the leader.
+  // A first-party Opus ID here is what sent mapped third-party teammates
+  // (cc-switch DeepSeek, etc.) to the upstream's most expensive model.
+  return leaderModel ?? getHardcodedTeammateModelFallback()
 }
 
 /**
@@ -126,7 +125,7 @@ export function resolveTeammateModel(
     if (invocationModel.toLowerCase() === 'inherit') {
       return leaderModel ?? getDefaultTeammateModel(leaderModel)
     }
-    return invocationModel
+    return parseUserSpecifiedModel(invocationModel)
   }
 
   if (hasAgentDefinition) {
@@ -135,15 +134,18 @@ export function resolveTeammateModel(
       definitionModel &&
       definitionModel.toLowerCase() !== 'inherit'
     ) {
-      return definitionModel
+      // Agent page / frontmatter is the highest teammate-specific pin.
+      // Resolve aliases so `opus` on a mapped provider becomes that
+      // provider's opus slot, not a first-party Opus ID.
+      return parseUserSpecifiedModel(definitionModel)
     }
     // Official Agent frontmatter defaults to `inherit`, so a selected Agent
     // follows the leader when its model is omitted or explicitly inherit.
     return leaderModel ?? getDefaultTeammateModel(leaderModel)
   }
 
-  // Plain teammates retain the existing /config teammateDefaultModel
-  // contract. Do not let the presence of a leader bypass that setting.
+  // Plain teammates: a pinned /config teammateDefaultModel still wins;
+  // otherwise follow the leader (same as an Agent whose model is inherit).
   return getDefaultTeammateModel(leaderModel)
 }
 

src/utils/config.ts

@@ -536,7 +536,7 @@ export type GlobalConfig = {
   // Teammate spawn mode: 'auto' | 'tmux' | 'in-process'
   teammateMode?: 'auto' | 'tmux' | 'in-process' // How to spawn teammates (default: 'auto')
   // Model for new teammates when the tool call doesn't pass one.
-  // undefined = hardcoded Opus (backward-compat); null = leader's model; string = model alias/ID.
+  // undefined/null = leader's model; string = model alias/ID.
   teammateDefaultModel?: string | null
 
   // PR status footer configuration (feature-flagged via GrowthBook)

src/utils/model/fable.test.ts

@@ -31,6 +31,7 @@ const ENV_KEYS = [
   'ANTHROPIC_MODEL',
   'ANTHROPIC_DEFAULT_FABLE_MODEL',
   'ANTHROPIC_DEFAULT_FABLE_MODEL_SUPPORTED_CAPABILITIES',
+  'ANTHROPIC_DEFAULT_OPUS_MODEL',
   'CLAUDE_CODE_DISABLE_1M_CONTEXT',
   'CLAUDE_CODE_USE_BEDROCK',
   'CLAUDE_CODE_SUBAGENT_MODEL',
@@ -182,6 +183,10 @@ describe('Fable model configuration', () => {
     expect(sanitizeModelName('claude-sonnet-5-experimental')).toBe('claude-sonnet-5')
     expect(getHardcodedTeammateModelFallback()).toBe('claude-opus-4-8')
 
+    process.env.ANTHROPIC_DEFAULT_OPUS_MODEL = 'deepseek-flash'
+    expect(getHardcodedTeammateModelFallback()).toBe('deepseek-flash')
+    delete process.env.ANTHROPIC_DEFAULT_OPUS_MODEL
+
     process.env.CLAUDE_CODE_USE_BEDROCK = '1'
     expect(getHardcodedTeammateModelFallback()).toBe(
       CLAUDE_OPUS_4_6_CONFIG.bedrock,

src/utils/swarm/teammateModel.ts

@@ -3,9 +3,14 @@ import { getAPIProvider } from '../model/providers.js'
 
 // @[MODEL LAUNCH]: Update the fallback model below.
 // When the user has never set teammateDefaultModel in /config, new teammates
-// use the current Opus default. Must be provider-aware so Bedrock/Vertex/Foundry
-// customers get a conservative provider ID.
+// use the current Opus default. Honor ANTHROPIC_DEFAULT_OPUS_MODEL first so a
+// mapped third-party provider (cc-switch DeepSeek, etc.) is not rewritten to a
+// first-party Opus ID that the upstream then bills as its most expensive model.
+// Bedrock/Vertex/Foundry still get a conservative provider ID.
 export function getHardcodedTeammateModelFallback(): string {
+  const mappedOpus = process.env.ANTHROPIC_DEFAULT_OPUS_MODEL?.trim()
+  if (mappedOpus) return mappedOpus
+
   const provider = getAPIProvider()
   return provider === 'firstParty'
     ? CLAUDE_OPUS_4_8_CONFIG.firstParty