feat: add Gemini 3.1 Flash Lite model

packages/core/src/model-registry.test.ts

@@ -30,6 +30,7 @@ describe('model registry', () => {
       'antigravity-claude-opus-4-6-thinking',
       'antigravity-claude-sonnet-4-6-thinking',
       'antigravity-gemini-3.1-flash-image',
+      'antigravity-gemini-3.1-flash-lite',
       'antigravity-gemini-3.1-pro',
       'antigravity-gemini-3.5-flash',
       'antigravity-gemini-3.6-flash',
@@ -104,4 +105,14 @@ describe('model registry', () => {
       },
     })
   })
+
+  it('registers flash-lite as a non-thinking text model', () => {
+    expect(
+      getPublicModelDefinitions()['antigravity-gemini-3.1-flash-lite'],
+    ).toMatchObject({
+      reasoning: false,
+      limit: { context: 1048576, output: 65535 },
+      modalities: { input: ['text'], output: ['text'] },
+    })
+  })
 })

packages/core/src/model-registry.ts

@@ -104,6 +104,15 @@ const ALL_MODEL_DEFINITIONS: OpencodeModelDefinitions = {
       high: { thinkingLevel: 'high' },
     },
   }),
+  'antigravity-gemini-3.1-flash-lite': defineModel(
+    'antigravity-gemini-3.1-flash-lite',
+    {
+      name: 'Gemini 3.1 Flash Lite (Antigravity)',
+      reasoning: false,
+      limit: { context: 1048576, output: 65535 },
+      modalities: { input: ['text'], output: ['text'] },
+    },
+  ),
   'antigravity-gemini-3.6-flash': defineModel('antigravity-gemini-3.6-flash', {
     name: 'Gemini 3.6 Flash (Antigravity)',
     reasoning: true,
@@ -291,6 +300,7 @@ const QUOTA_GROUP_BY_MODEL_ID: Record<string, ModelQuotaGroup> = {
   'gemini-3.1-pro-high': 'gemini-pro',
   'gemini-3-flash': 'gemini-flash',
   'gemini-3-flash-agent': 'gemini-flash',
+  'gemini-3.1-flash-lite': 'gemini-flash',
   'gemini-3.5-flash-low': 'gemini-flash',
   'gemini-3.5-flash-extra-low': 'gemini-flash',
   'gemini-3.6-flash-low': 'gemini-flash',
@@ -304,6 +314,7 @@ const QUOTA_GROUP_BY_MODEL_ID: Record<string, ModelQuotaGroup> = {
 
 const ANTIGRAVITY_OPENCODE_MODEL_IDS = [
   'antigravity-gemini-3.6-flash',
+  'antigravity-gemini-3.1-flash-lite',
   'antigravity-gemini-3.5-flash',
   'antigravity-gemini-3.1-pro',
   'antigravity-claude-sonnet-4-6-thinking',

packages/core/src/transform/model-resolver.test.ts

@@ -74,6 +74,63 @@ describe('resolveModelWithTier', () => {
     })
   })
 
+  describe('Gemini 3.1 Flash Lite Antigravity route', () => {
+    it('resolves as a non-thinking text model', () => {
+      const result = resolveModelWithTier('antigravity-gemini-3.1-flash-lite')
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.thinkingBudget).toBeUndefined()
+      expect(result.thinkingLevel).toBeUndefined()
+      expect(result.tier).toBeUndefined()
+      expect(result.quotaPreference).toBe('antigravity')
+    })
+
+    it('maps gemini-3.1-flash-lite directly for the header-style path', () => {
+      const result = resolveModelForHeaderStyle(
+        'gemini-3.1-flash-lite',
+        'antigravity',
+      )
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.quotaPreference).toBe('antigravity')
+    })
+
+    // Tier-suffixed flash-lite must NOT carry thinkingLevel / tier on
+    // any quota path — flash-lite does not support thinking.
+    it('drops tier suffix on antigravity header-style path', () => {
+      const result = resolveModelForHeaderStyle(
+        'gemini-3.1-flash-lite-high',
+        'antigravity',
+      )
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.thinkingLevel).toBeUndefined()
+      expect(result.tier).toBeUndefined()
+      expect(result.quotaPreference).toBe('antigravity')
+    })
+
+    it('drops tier suffix on gemini-cli header-style path', () => {
+      const result = resolveModelForHeaderStyle(
+        'gemini-3.1-flash-lite-high',
+        'gemini-cli',
+      )
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.thinkingLevel).toBeUndefined()
+      expect(result.tier).toBeUndefined()
+      expect(result.quotaPreference).toBe('gemini-cli')
+    })
+
+    it('drops tier suffix on direct resolveModelWithTier call', () => {
+      const result = resolveModelWithTier('gemini-3.1-flash-lite-high')
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.thinkingLevel).toBeUndefined()
+      expect(result.tier).toBeUndefined()
+      expect(result.quotaPreference).toBe('antigravity')
+    })
+  })
+
   describe('Gemini 3.6 Flash Antigravity routes', () => {
     it.each([
       [
@@ -475,6 +532,18 @@ describe('Issue #103: resolveModelForHeaderStyle', () => {
       expect(result.thinkingLevel).toBe('medium')
       expect(result.quotaPreference).toBe('gemini-cli')
     })
+
+    it('resolves gemini-3.1-flash-lite as non-thinking on gemini-cli path', () => {
+      const result = resolveModelForHeaderStyle(
+        'gemini-3.1-flash-lite',
+        'gemini-cli',
+      )
+      expect(result.actualModel).toBe('gemini-3.1-flash-lite')
+      expect(result.isThinkingModel).toBe(false)
+      expect(result.thinkingLevel).toBeUndefined()
+      expect(result.thinkingBudget).toBeUndefined()
+      expect(result.quotaPreference).toBe('gemini-cli')
+    })
   })
 
   describe('no transformation needed', () => {

packages/core/src/transform/model-resolver.ts

@@ -214,6 +214,7 @@ export function resolveModelWithTier(
   const isGemini31Pro = /^gemini-3\.1-pro/i.test(baseName)
   const isGemini35Flash = /^gemini-3\.5-flash/i.test(baseName)
   const isGemini36Flash = /^gemini-3\.6-flash/i.test(baseName)
+  const isGemini31FlashLite = /^gemini-3\.1-flash-lite/i.test(baseName)
   const isGptOss120b = /^gpt-oss-120b(?:-medium)?$/i.test(baseName)
 
   if (isGemini31Pro && quotaPreference === 'antigravity') {
@@ -249,6 +250,16 @@ export function resolveModelWithTier(
     }
   }
 
+  // Flash-lite is text-only and non-thinking on every quota path.
+  if (isGemini31FlashLite) {
+    return {
+      actualModel: 'gemini-3.1-flash-lite',
+      isThinkingModel: false,
+      quotaPreference,
+      explicitQuota,
+    }
+  }
+
   if (isGptOss120b && quotaPreference === 'antigravity') {
     return {
       actualModel: 'gpt-oss-120b-medium',
@@ -428,11 +439,15 @@ export function resolveModelForHeaderStyle(
     const isGemini35Flash = isGemini35FlashModel(
       transformedModel.replace(TIER_REGEX, ''),
     )
+    const isGemini31FlashLite = /^gemini-3\.1-flash-lite/i.test(
+      transformedModel,
+    )
 
-    // Don't add tier suffix to image models - they don't support thinking
+    // Don't add tier suffix to image or flash-lite models - they don't support thinking
     if (
       (isGemini3Pro || isGemini3Flash) &&
       !isGemini35Flash &&
+      !isGemini31FlashLite &&
       !hasTierSuffix &&
       !isImageModel
     ) {
@@ -456,13 +471,30 @@ export function resolveModelForHeaderStyle(
     // gemini-3-flash-preview bucket; retrieveUserQuota does not list a
     // gemini-3.5-flash bucket for the gemini-cli header path.
     const isGemini35Flash = isGemini35FlashModel(transformedModel)
+    // Flash-lite has no -preview CLI variant — keep the plain wire id.
+    const isGemini31FlashLite = /^gemini-3\.1-flash-lite$/i.test(
+      transformedModel,
+    )
     if (isGemini35Flash) {
       transformedModel = getGemini35FlashGeminiCliFallbackModel()
+    } else if (isGemini31FlashLite) {
+      // No transformation needed — flash-lite resolves as non-thinking
+      // and has no distinct CLI preview model.
     } else if (!hasPreviewSuffix) {
       transformedModel = `${transformedModel}-preview`
     }
 
     const resolved = resolveModelWithTier(transformedModel, { cli_first: true })
+
+    // Flash-lite is non-thinking — don't pass through requestedTier even if a
+    // tier suffix was on the original request.
+    if (isGemini31FlashLite) {
+      return {
+        ...resolved,
+        quotaPreference: 'gemini-cli',
+      }
+    }
+
     return {
       ...resolved,
       thinkingLevel: requestedTier ?? resolved.thinkingLevel,

packages/opencode/script/test-models.ts

@@ -14,6 +14,10 @@ const MODELS: ModelTest[] = [
   { model: 'google/gemini-3.5-flash-preview', category: 'gemini-cli' },
 
   // Antigravity Gemini
+  {
+    model: 'google/antigravity-gemini-3.1-flash-lite',
+    category: 'antigravity-gemini',
+  },
   {
     model: 'google/antigravity-gemini-3.6-flash-low',
     category: 'antigravity-gemini',

packages/opencode/src/plugin/config/models.test.ts

@@ -18,6 +18,7 @@ describe('OPENCODE_MODEL_DEFINITIONS', () => {
       'antigravity-claude-opus-4-6-thinking',
       'antigravity-claude-sonnet-4-6-thinking',
       'antigravity-gemini-3.1-flash-image',
+      'antigravity-gemini-3.1-flash-lite',
       'antigravity-gemini-3.1-pro',
       'antigravity-gemini-3.5-flash',
       'antigravity-gemini-3.6-flash',
@@ -52,6 +53,17 @@ describe('OPENCODE_MODEL_DEFINITIONS', () => {
     })
   })
 
+  it('registers flash-lite without thinking variants', () => {
+    expect(getModel('antigravity-gemini-3.1-flash-lite')).toMatchObject({
+      reasoning: false,
+      limit: { context: 1048576, output: 65535 },
+      modalities: { input: ['text'], output: ['text'] },
+    })
+    expect(
+      getModel('antigravity-gemini-3.1-flash-lite').variants,
+    ).toBeUndefined()
+  })
+
   it('disables unsupported automatic Claude budget variants', () => {
     expect(getModel('antigravity-claude-opus-4-6-thinking').variants).toEqual({
       low: { disabled: true },

packages/opencode/src/plugin/quota.test.ts

@@ -53,6 +53,9 @@ describe('classifyQuotaGroup', () => {
         'Gemini 3.6 Flash (Medium)',
       ),
     ).toBe('gemini-flash')
+    expect(
+      classifyQuotaGroup('gemini-3.1-flash-lite', 'Gemini 3.1 Flash Lite'),
+    ).toBe('gemini-flash')
     expect(classifyQuotaGroup('gemini-pro-agent', 'Gemini 3.1 Pro')).toBe(
       'gemini-pro',
     )

packages/opencode/src/plugin/request.test.ts

@@ -1611,6 +1611,33 @@ describe('request.ts', () => {
       })
     })
 
+    it('builds the AGY 1.1.6 request for gemini-3.1-flash-lite as a non-thinking model', () => {
+      const result = prepareAntigravityRequest(
+        'https://generativelanguage.googleapis.com/v1beta/models/antigravity-gemini-3.1-flash-lite:generateContent',
+        {
+          method: 'POST',
+          body: JSON.stringify({
+            contents: [
+              { role: 'user', parts: [{ text: 'Reply with FLASHLITE_OK' }] },
+            ],
+            generationConfig: { maxOutputTokens: 1024 },
+          }),
+        },
+        mockAccessToken,
+        mockProjectId,
+        undefined,
+        'antigravity',
+      )
+
+      const wrapped = JSON.parse(result.init.body as string)
+      expect(result.effectiveModel).toBe('gemini-3.1-flash-lite')
+      expect(wrapped.model).toBe('gemini-3.1-flash-lite')
+      expect(wrapped.request.generationConfig).toMatchObject({
+        maxOutputTokens: 65535,
+      })
+      expect(wrapped.request.generationConfig.thinkingConfig).toBeUndefined()
+    })
+
     it('builds the live Gemini 3.1 Flash Image request shape', () => {
       const result = prepareAntigravityRequest(
         'https://generativelanguage.googleapis.com/v1beta/models/antigravity-gemini-3.1-flash-image:generateContent',

packages/opencode/src/plugin/request.ts

@@ -202,6 +202,9 @@ function getAgyMaxOutputTokens(model: string): number | undefined {
   ) {
     return 65536
   }
+  if (lower === 'gemini-3.1-flash-lite') {
+    return 65535
+  }
   if (lower === 'gemini-3.1-pro-low' || lower === 'gemini-pro-agent') {
     return 65535
   }

packages/pi/src/index.test.ts

@@ -14,16 +14,27 @@ describe('Pi Antigravity model catalog', () => {
         models: Array<{
           id: string
           reasoning: boolean
+          input: Array<string>
           contextWindow: number
           maxTokens: number
         }>
       },
     ]
     const modelIds = config.models.map((model) => model.id)
 
+    expect(modelIds).toContain('antigravity-gemini-3.1-flash-lite')
     expect(modelIds).toContain('antigravity-gemini-3.6-flash')
     expect(modelIds).toContain('antigravity-gpt-oss-120b-medium')
     expect(modelIds).not.toContain('antigravity-gemini-3.1-flash-image')
+    const flashLite = config.models.find(
+      (model) => model.id === 'antigravity-gemini-3.1-flash-lite',
+    )
+    expect(flashLite).toMatchObject({
+      reasoning: false,
+      contextWindow: 1048576,
+      maxTokens: 65535,
+    })
+    expect(flashLite!.input).toEqual(['text'])
     expect(
       config.models.find(
         (model) => model.id === 'antigravity-gemini-3.6-flash',

packages/pi/src/index.ts

@@ -15,8 +15,15 @@ import { streamCortexKitAntigravity } from './stream.ts'
 
 const ANTIGRAVITY_PROVIDER_ID = 'google-antigravity'
 
-function textImageInput(): Array<'text' | 'image'> {
-  return ['text', 'image']
+/** Derive Pi-compatible input modalities from the model registry, keeping
+ * selectable capabilities consistent with the source of truth.
+ * Pi's protocol only supports 'text' and 'image' input types. */
+function modelInput(modalities: {
+  input: Array<string>
+}): Array<'text' | 'image'> {
+  return modalities.input.filter(
+    (m): m is 'text' | 'image' => m === 'text' || m === 'image',
+  )
 }
 
 async function loginAntigravity(
@@ -84,7 +91,7 @@ export default function cortexKitPiAntigravityAuth(pi: ExtensionAPI): void {
       id: model.id,
       name: model.name,
       reasoning: model.reasoning,
-      input: textImageInput(),
+      input: modelInput(model.modalities),
       cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
       contextWindow: model.limit.context,
       maxTokens: model.limit.output,