diff --git a/docs/roadmap/05-delta-types.md b/docs/roadmap/05-delta-types.md
new file mode 100644
index 00000000000..920f6c5796c
--- /dev/null
+++ b/docs/roadmap/05-delta-types.md
@@ -0,0 +1,138 @@
+# Decouple from @google/genai Types
+
+## Branch: `refactor/delta-types`
+
+## Problem
+
+67 files import from `@google/genai`. Every provider converts to/from Google's
+type system, which means:
+
+- Google-specific concepts (`safetyRatings`, `promptFeedback`,
+  `FinishReason.FINISH_REASON_UNSPECIFIED`) leak into non-Google responses as
+  empty placeholders
+- Provider-specific features (Anthropic citations, OpenAI structured outputs,
+  think blocks) can't be represented without extending Google's types
+- Tight coupling to a third-party type system makes upgrades risky — a breaking
+  change in `@google/genai` ripples through the entire codebase
+
+## Approach
+
+Define Delta-native types as the canonical interchange format. Google types
+become one translation layer among many, not the canonical truth.
+
+## Plan
+
+### Phase 1: Define `packages/core/src/types/delta.ts`
+
+Core types that map to what Delta actually needs:
+
+```typescript
+// The Delta canonical message format — what flows between providers and the UI
+interface DeltaMessage {
+  role: 'user' | 'assistant' | 'system';
+  parts: DeltaPart[];
+}
+
+type DeltaPart =
+  | { type: 'text'; text: string }
+  | { type: 'functionCall'; id: string; name: string; args: Record<string, unknown> }
+  | { type: 'functionResponse'; id: string; name: string; response: unknown }
+  | { type: 'thinking'; text: string }           // reasoning models
+  | { type: 'image'; mimeType: string; data: string }  // vision
+  | { type: 'citation'; source: string; text: string }; // Anthropic citations etc.
+
+interface DeltaResponse {
+  id: string;
+  model: string;
+  parts: DeltaPart[];
+  finishReason: DeltaFinishReason;
+  usage?: DeltaUsage;
+}
+
+enum DeltaFinishReason {
+  STOP = 'stop',
+  MAX_TOKENS = 'max_tokens',
+  TOOL_USE = 'tool_use',
+  ERROR = 'error',
+  UNSPECIFIED = 'unspecified',
+}
+
+interface DeltaUsage {
+  inputTokens: number;
+  outputTokens: number;
+  totalTokens: number;
+  cachedTokens?: number;
+}
+
+interface DeltaToolDeclaration {
+  name: string;
+  description: string;
+  parameters: Record<string, unknown>; // JSON Schema
+}
+
+interface DeltaGenerateRequest {
+  messages: DeltaMessage[];
+  tools?: DeltaToolDeclaration[];
+  systemPrompt?: string;
+  config?: DeltaGenerateConfig;
+}
+
+interface DeltaGenerateConfig {
+  maxOutputTokens?: number;
+  temperature?: number;
+  topP?: number;
+  topK?: number;
+  stopSequences?: string[];
+}
+```
+
+### Phase 2: Create adapter layer per provider
+
+```
+packages/core/src/adapters/
+  googleAdapter.ts    — DeltaMessage ↔ @google/genai types
+  openaiAdapter.ts    — DeltaMessage ↔ OpenAI SDK types
+  anthropicAdapter.ts — DeltaMessage ↔ Anthropic SDK types
+```
+
+Each adapter exports `toProviderFormat()` and `fromProviderFormat()`. The
+content generators call these instead of doing inline conversion.
+
+### Phase 3: Migrate ContentGenerator interface
+
+Change the interface signature from Google types to Delta types:
+
+```typescript
+interface ContentGenerator {
+  generateContent(request: DeltaGenerateRequest): Promise<DeltaResponse>;
+  generateContentStream(request: DeltaGenerateRequest): AsyncGenerator<DeltaResponse>;
+  countTokens(messages: DeltaMessage[]): Promise<number>;
+}
+```
+
+### Phase 4: Migrate consumers (67 files)
+
+This is the bulk of the work. Grep for all `@google/genai` imports and replace
+with Delta types. The Google backend's adapter handles the actual SDK calls.
+
+**Migration strategy**: do it file-by-file, keeping both type systems working
+during the transition via a compatibility shim. Remove the shim once all files
+are migrated.
+
+## Files to create
+- `packages/core/src/types/delta.ts` — canonical types
+- `packages/core/src/adapters/googleAdapter.ts`
+- `packages/core/src/adapters/openaiAdapter.ts`
+- `packages/core/src/adapters/anthropicAdapter.ts`
+- Tests for each adapter
+
+## Scope warning
+
+This is the largest refactor. It touches 67+ files. Should be done after
+branches 1-4 are merged to avoid merge hell.
+
+## Dependencies
+- Should merge AFTER `fix/anthropic-provider` (branch 1) — otherwise the
+  Anthropic adapter would be written against the broken raw-fetch implementation
+- Should merge AFTER `feature/schema-normalization` (branch 2) — schema
+  normalization can be built into the adapter layer cleanly
diff --git a/packages/cli/src/nonInteractiveCli.ts b/packages/cli/src/nonInteractiveCli.ts
index bccb6dae8be..11097516867 100644
--- a/packages/cli/src/nonInteractiveCli.ts
+++ b/packages/cli/src/nonInteractiveCli.ts
@@ -4,6 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Content,
+  Part,
+  FunctionCall,
+} from '../../core/src/types/delta.js';
 import {
   Config,
   ToolCallRequestInfo,
@@ -15,7 +20,6 @@ import {
   ToolErrorType,
   parseAndFormatApiError,
 } from '@delta-code/delta-code-core';
-import { Content, Part, FunctionCall } from '@google/genai';
 
 import { ConsolePatcher } from './ui/utils/ConsolePatcher.js';
 
diff --git a/packages/cli/src/ui/commands/types.ts b/packages/cli/src/ui/commands/types.ts
index b564d4d3a93..e3fcd648c22 100644
--- a/packages/cli/src/ui/commands/types.ts
+++ b/packages/cli/src/ui/commands/types.ts
@@ -4,8 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Content,
+} from '../../../../core/src/types/delta.js';
 import { type ReactNode } from 'react';
-import { Content } from '@google/genai';
+
 import { HistoryItemWithoutId } from '../types.js';
 import { Config, GitService, Logger } from '@delta-code/delta-code-core';
 import { LoadedSettings } from '../../config/settings.js';
diff --git a/packages/cli/src/ui/hooks/atCommandProcessor.ts b/packages/cli/src/ui/hooks/atCommandProcessor.ts
index 18a0ee4569e..74c41e133e9 100644
--- a/packages/cli/src/ui/hooks/atCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/atCommandProcessor.ts
@@ -4,9 +4,13 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartListUnion,
+  PartUnion,
+} from '../../../../core/src/types/delta.js';
 import * as fs from 'fs/promises';
 import * as path from 'path';
-import { PartListUnion, PartUnion } from '@google/genai';
+
 import {
   AnyToolInvocation,
   Config,
diff --git a/packages/cli/src/ui/hooks/shellCommandProcessor.ts b/packages/cli/src/ui/hooks/shellCommandProcessor.ts
index aaef5171df0..a13429ede86 100644
--- a/packages/cli/src/ui/hooks/shellCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/shellCommandProcessor.ts
@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartListUnion,
+} from '../../../../core/src/types/delta.js';
 import {
   HistoryItemWithoutId,
   IndividualToolCallDisplay,
@@ -17,7 +20,7 @@ import {
   ShellExecutionResult,
   ShellExecutionService,
 } from '@delta-code/delta-code-core';
-import { type PartListUnion } from '@google/genai';
+
 import { UseHistoryManagerReturn } from './useHistoryManager.js';
 import { SHELL_COMMAND_NAME } from '../constants.js';
 import { formatMemoryUsage } from '../utils/formatters.js';
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
index b0015d6db94..2a2100f136c 100644
--- a/packages/cli/src/ui/hooks/slashCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
@@ -4,8 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartListUnion,
+} from '../../../../core/src/types/delta.js';
 import { useCallback, useMemo, useEffect, useState } from 'react';
-import { type PartListUnion } from '@google/genai';
+
 import process from 'node:process';
 import { UseHistoryManagerReturn } from './useHistoryManager.js';
 import { useStateAndRef } from './useStateAndRef.js';
diff --git a/packages/cli/src/ui/hooks/useDeltaStream.ts b/packages/cli/src/ui/hooks/useDeltaStream.ts
index 460a84c67b3..2e5b129a2f0 100644
--- a/packages/cli/src/ui/hooks/useDeltaStream.ts
+++ b/packages/cli/src/ui/hooks/useDeltaStream.ts
@@ -4,7 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { type Part, type PartListUnion, FinishReason } from '@google/genai';
+import {
+  Part,
+  PartListUnion,
+  FinishReason,
+} from '../../../../core/src/types/delta.js';
 import {
   Config,
   ServerDeltaContentEvent as ContentEvent,
diff --git a/packages/cli/src/zed-integration/zedIntegration.ts b/packages/cli/src/zed-integration/zedIntegration.ts
index 1dc41d9f757..61f59a55e5f 100644
--- a/packages/cli/src/zed-integration/zedIntegration.ts
+++ b/packages/cli/src/zed-integration/zedIntegration.ts
@@ -4,9 +4,14 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Content,
+  FunctionCall,
+  Part,
+  PartListUnion,
+} from '../../../core/src/types/delta.js';
 import { ReadableStream, WritableStream } from 'node:stream/web';
 
-import { Content, FunctionCall, Part, PartListUnion } from '@google/genai';
 import {
   AuthType,
   clearCachedCredentialFile,
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 5861e9ed18a..ed3c98202cd 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -13,7 +13,7 @@ import {
   GenerateContentResponse,
   FunctionDeclaration,
   Schema,
-} from '@google/genai';
+} from '../types/delta.js';
 import {
   getDirectoryContextString,
   getEnvironmentContext,
diff --git a/packages/core/src/core/coreToolScheduler.ts b/packages/core/src/core/coreToolScheduler.ts
index fac06882d58..f92d69c876c 100644
--- a/packages/core/src/core/coreToolScheduler.ts
+++ b/packages/core/src/core/coreToolScheduler.ts
@@ -4,6 +4,10 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Part,
+  PartListUnion,
+} from '../types/delta.js';
 import {
   ToolCallRequestInfo,
   ToolCallResponseInfo,
@@ -23,7 +27,7 @@ import {
   AnyToolInvocation,
 } from '../index.js';
 import { HookManager } from '../hooks/hookManager.js';
-import { Part, PartListUnion } from '@google/genai';
+
 import { getResponseTextFromParts } from '../utils/generateContentResponseUtilities.js';
 import {
   isModifiableDeclarativeTool,
diff --git a/packages/core/src/core/deltaChat.ts b/packages/core/src/core/deltaChat.ts
index f0605d46853..6a75a807c22 100644
--- a/packages/core/src/core/deltaChat.ts
+++ b/packages/core/src/core/deltaChat.ts
@@ -11,10 +11,12 @@ import {
   GenerateContentResponse,
   Content,
   GenerateContentConfig,
-  SendMessageParameters,
-  createUserContent,
   Part,
   Tool,
+} from '../types/delta.js';
+import {
+  SendMessageParameters,
+  createUserContent,
 } from '@google/genai';
 import { retryWithBackoff } from '../utils/retry.js';
 import { isFunctionResponse } from '../utils/messageInspectors.js';
diff --git a/packages/core/src/core/deltaRequest.ts b/packages/core/src/core/deltaRequest.ts
index a26301f59df..4d44a935be6 100644
--- a/packages/core/src/core/deltaRequest.ts
+++ b/packages/core/src/core/deltaRequest.ts
@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { type PartListUnion } from '@google/genai';
+import {
+  PartListUnion,
+} from '../types/delta.js';
 import { partToString } from '../utils/partUtils.js';
 
 /**
diff --git a/packages/core/src/core/logger.ts b/packages/core/src/core/logger.ts
index 71be7d8d179..68c7c1ca977 100644
--- a/packages/core/src/core/logger.ts
+++ b/packages/core/src/core/logger.ts
@@ -4,9 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Content,
+} from '../types/delta.js';
 import path from 'node:path';
 import { promises as fs } from 'node:fs';
-import { Content } from '@google/genai';
+
 import { getProjectTempDir } from '../utils/paths.js';
 
 const LOG_FILE_NAME = 'logs.json';
diff --git a/packages/core/src/core/subagent.ts b/packages/core/src/core/subagent.ts
index 3f2b0d3c645..f2c5ca6f848 100644
--- a/packages/core/src/core/subagent.ts
+++ b/packages/core/src/core/subagent.ts
@@ -4,13 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { reportError } from '../utils/errorReporting.js';
-import { ToolRegistry } from '../tools/tool-registry.js';
-import { Config } from '../config/config.js';
-import { ToolCallRequestInfo } from './turn.js';
-import { executeToolCall } from './nonInteractiveToolExecutor.js';
-import { createContentGenerator } from './contentGenerator.js';
-import { getEnvironmentContext } from '../utils/environmentContext.js';
 import {
   Content,
   Part,
@@ -18,7 +11,15 @@ import {
   GenerateContentConfig,
   FunctionDeclaration,
   Type,
-} from '@google/genai';
+} from '../types/delta.js';
+import { reportError } from '../utils/errorReporting.js';
+import { ToolRegistry } from '../tools/tool-registry.js';
+import { Config } from '../config/config.js';
+import { ToolCallRequestInfo } from './turn.js';
+import { executeToolCall } from './nonInteractiveToolExecutor.js';
+import { createContentGenerator } from './contentGenerator.js';
+import { getEnvironmentContext } from '../utils/environmentContext.js';
+
 import { DeltaChat } from './deltaChat.js';
 
 /**
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index 23e17a09b63..02d0b89877b 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -10,7 +10,7 @@ import {
   FunctionCall,
   FunctionDeclaration,
   FinishReason,
-} from '@google/genai';
+} from '../types/delta.js';
 import {
   ToolCallConfirmationDetails,
   ToolResult,
diff --git a/packages/core/src/telemetry/types.ts b/packages/core/src/telemetry/types.ts
index 9bc9f0a0050..ea984cf02db 100644
--- a/packages/core/src/telemetry/types.ts
+++ b/packages/core/src/telemetry/types.ts
@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { GenerateContentResponseUsageMetadata } from '@google/genai';
+import {
+  GenerateContentResponseUsageMetadata,
+} from '../types/delta.js';
 import { Config } from '../config/config.js';
 import { CompletedToolCall } from '../core/coreToolScheduler.js';
 import { FileDiff } from '../tools/tools.js';
diff --git a/packages/core/src/test-utils/tools.ts b/packages/core/src/test-utils/tools.ts
index da64221262f..0137a7332ee 100644
--- a/packages/core/src/test-utils/tools.ts
+++ b/packages/core/src/test-utils/tools.ts
@@ -4,6 +4,10 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Schema,
+  Type,
+} from '../types/delta.js';
 import { vi } from 'vitest';
 import {
   BaseTool,
@@ -11,7 +15,6 @@ import {
   ToolResult,
   Kind,
 } from '../tools/tools.js';
-import { Schema, Type } from '@google/genai';
 
 /**
  * A highly configurable mock tool for testing purposes.
diff --git a/packages/core/src/tools/checkpoint.ts b/packages/core/src/tools/checkpoint.ts
index 64540ee3ae7..626ffbbf854 100644
--- a/packages/core/src/tools/checkpoint.ts
+++ b/packages/core/src/tools/checkpoint.ts
@@ -8,13 +8,16 @@
  * persistent, semantically-searchable change ledger across sessions.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'node:fs/promises';
 import * as path from 'node:path';
 import { getOpenBrainClient } from '../services/openBrainClient.js';
diff --git a/packages/core/src/tools/diffPreview.ts b/packages/core/src/tools/diffPreview.ts
index 789806522bc..993b4e1e06e 100644
--- a/packages/core/src/tools/diffPreview.ts
+++ b/packages/core/src/tools/diffPreview.ts
@@ -5,13 +5,16 @@
  * Uses the `diff` package (already a dependency) to generate unified diffs.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'node:fs/promises';
 import { createPatch } from 'diff';
 
diff --git a/packages/core/src/tools/fileSummary.ts b/packages/core/src/tools/fileSummary.ts
index 8301f436b81..0c5d67bd92d 100644
--- a/packages/core/src/tools/fileSummary.ts
+++ b/packages/core/src/tools/fileSummary.ts
@@ -8,13 +8,16 @@
  * the shared AST extraction layer for better accuracy.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'node:fs/promises';
 import * as path from 'node:path';
 
diff --git a/packages/core/src/tools/lint.ts b/packages/core/src/tools/lint.ts
index 9589ee40853..c4e6b7c248f 100644
--- a/packages/core/src/tools/lint.ts
+++ b/packages/core/src/tools/lint.ts
@@ -2,13 +2,16 @@
  * Lint tool — auto-detect and run the project linter with structured output.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import { execSync } from 'node:child_process';
 import { detectProjectCommands } from './diagnostics/projectDetector.js';
 import { parseGenericDiagnostics, formatDiagnostics } from './diagnostics/outputParsers.js';
diff --git a/packages/core/src/tools/mcp-client.ts b/packages/core/src/tools/mcp-client.ts
index c0cd632289c..88c6b914d0e 100644
--- a/packages/core/src/tools/mcp-client.ts
+++ b/packages/core/src/tools/mcp-client.ts
@@ -4,6 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
+import {
+  mcpToTool,
+} from '@google/genai';
 import { Client } from '@modelcontextprotocol/sdk/client/index.js';
 import { Transport } from '@modelcontextprotocol/sdk/shared/transport.js';
 import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
@@ -27,7 +33,6 @@ import { AuthProviderType, MCPServerConfig } from '../config/config.js';
 import { GoogleCredentialProvider } from '../mcp/google-auth-provider.js';
 import { DiscoveredMCPTool } from './mcp-tool.js';
 
-import { FunctionDeclaration, mcpToTool } from '@google/genai';
 import { ToolRegistry } from './tool-registry.js';
 import { PromptRegistry } from '../prompts/prompt-registry.js';
 import { MCPOAuthProvider } from '../mcp/oauth-provider.js';
diff --git a/packages/core/src/tools/mcp-tool.ts b/packages/core/src/tools/mcp-tool.ts
index fbb104fde92..1fef5011000 100644
--- a/packages/core/src/tools/mcp-tool.ts
+++ b/packages/core/src/tools/mcp-tool.ts
@@ -4,6 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  CallableTool,
+  FunctionCall,
+  Part,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
@@ -14,7 +19,6 @@ import {
   ToolMcpConfirmationDetails,
   ToolResult,
 } from './tools.js';
-import { CallableTool, FunctionCall, Part } from '@google/genai';
 
 type ToolParams = Record<string, unknown>;
 
diff --git a/packages/core/src/tools/memoryTool.ts b/packages/core/src/tools/memoryTool.ts
index 4c2a9e0303e..6d2b2a5dd59 100644
--- a/packages/core/src/tools/memoryTool.ts
+++ b/packages/core/src/tools/memoryTool.ts
@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
@@ -12,7 +15,7 @@ import {
   ToolEditConfirmationDetails,
   ToolConfirmationOutcome,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'fs/promises';
 import * as path from 'path';
 import { homedir } from 'os';
diff --git a/packages/core/src/tools/multiEdit.ts b/packages/core/src/tools/multiEdit.ts
index 4c4ffd95f7a..348f5682738 100644
--- a/packages/core/src/tools/multiEdit.ts
+++ b/packages/core/src/tools/multiEdit.ts
@@ -6,13 +6,16 @@
  * This prevents partial refactors that leave the codebase in a broken state.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'node:fs/promises';
 
 interface EditEntry {
diff --git a/packages/core/src/tools/read-file.ts b/packages/core/src/tools/read-file.ts
index ecc2168d12e..861d3234a79 100644
--- a/packages/core/src/tools/read-file.ts
+++ b/packages/core/src/tools/read-file.ts
@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartUnion,
+} from '../types/delta.js';
 import path from 'path';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
@@ -16,7 +19,7 @@ import {
   ToolResult,
 } from './tools.js';
 import { ToolErrorType } from './tool-error.js';
-import { PartUnion } from '@google/genai';
+
 import {
   processSingleFileContent,
   getSpecificMimeType,
diff --git a/packages/core/src/tools/read-many-files.ts b/packages/core/src/tools/read-many-files.ts
index fd960767161..cfb0979e796 100644
--- a/packages/core/src/tools/read-many-files.ts
+++ b/packages/core/src/tools/read-many-files.ts
@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartListUnion,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
@@ -22,7 +25,7 @@ import {
   DEFAULT_ENCODING,
   getSpecificMimeType,
 } from '../utils/fileUtils.js';
-import { PartListUnion } from '@google/genai';
+
 import { Config, DEFAULT_FILE_FILTERING_OPTIONS } from '../config/config.js';
 import {
   recordFileOperationMetric,
diff --git a/packages/core/src/tools/repoMap.ts b/packages/core/src/tools/repoMap.ts
index 588674cefbd..00356227a76 100644
--- a/packages/core/src/tools/repoMap.ts
+++ b/packages/core/src/tools/repoMap.ts
@@ -10,13 +10,16 @@
  * in context or grep speculatively.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import { RepoIndex } from '../indexing/repoIndex.js';
 import { RegexSymbolExtractor } from '../indexing/symbolExtractor.js';
 import { Config } from '../config/config.js';
diff --git a/packages/core/src/tools/runTests.ts b/packages/core/src/tools/runTests.ts
index 686e5453f73..91865d95bd2 100644
--- a/packages/core/src/tools/runTests.ts
+++ b/packages/core/src/tools/runTests.ts
@@ -2,13 +2,16 @@
  * Test runner tool — auto-detect and run project tests with structured output.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import { execSync } from 'node:child_process';
 import { detectProjectCommands } from './diagnostics/projectDetector.js';
 import { parseGenericDiagnostics, formatDiagnostics } from './diagnostics/outputParsers.js';
diff --git a/packages/core/src/tools/think.ts b/packages/core/src/tools/think.ts
index c27655e4256..5cbdfab5267 100644
--- a/packages/core/src/tools/think.ts
+++ b/packages/core/src/tools/think.ts
@@ -9,13 +9,15 @@
  * make fewer cascading errors.
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
 
 interface ThinkParams {
   reasoning: string;
diff --git a/packages/core/src/tools/todoWrite.ts b/packages/core/src/tools/todoWrite.ts
index 656d4872dc4..4f02b80c26e 100644
--- a/packages/core/src/tools/todoWrite.ts
+++ b/packages/core/src/tools/todoWrite.ts
@@ -4,13 +4,16 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import {
   BaseDeclarativeTool,
   BaseToolInvocation,
   Kind,
   ToolResult,
 } from './tools.js';
-import { FunctionDeclaration } from '@google/genai';
+
 import * as fs from 'fs/promises';
 import * as fsSync from 'fs';
 import * as path from 'path';
@@ -129,7 +132,6 @@ The assistant used the todo list because:
 </reasoning>
 </example>
 
-
 <example>
 User: I need to implement these features for my e-commerce site: user registration, product catalog, shopping cart, and checkout flow.
 Assistant: I'll help implement these features. First, let's add all the features to the todo list.
diff --git a/packages/core/src/tools/tool-registry.ts b/packages/core/src/tools/tool-registry.ts
index 416ee99e4fc..9126865cce9 100644
--- a/packages/core/src/tools/tool-registry.ts
+++ b/packages/core/src/tools/tool-registry.ts
@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { FunctionDeclaration } from '@google/genai';
+import {
+  FunctionDeclaration,
+} from '../types/delta.js';
 import { AnyDeclarativeTool, Kind, ToolResult, BaseTool } from './tools.js';
 import { Config } from '../config/config.js';
 import { spawn } from 'node:child_process';
diff --git a/packages/core/src/tools/tools.ts b/packages/core/src/tools/tools.ts
index 55df57e8f90..35027f40f30 100644
--- a/packages/core/src/tools/tools.ts
+++ b/packages/core/src/tools/tools.ts
@@ -4,7 +4,10 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { FunctionDeclaration, PartListUnion } from '@google/genai';
+import {
+  FunctionDeclaration,
+  PartListUnion,
+} from '../types/delta.js';
 import { ToolErrorType } from './tool-error.js';
 import { DiffUpdateResult } from '../ide/ideContext.js';
 
diff --git a/packages/core/src/types/delta.ts b/packages/core/src/types/delta.ts
new file mode 100644
index 00000000000..c233269f9ee
--- /dev/null
+++ b/packages/core/src/types/delta.ts
@@ -0,0 +1,93 @@
+/**
+ * Delta type barrel — the single point of decoupling from @google/genai.
+ *
+ * All files in the codebase import from here instead of directly from the
+ * @google/genai SDK. This means:
+ * 1. Only this file depends on @google/genai types
+ * 2. When we replace the underlying types with native Delta definitions,
+ *    only this file changes — everything else keeps working
+ * 3. Provider-specific files (content generators, adapters) still import
+ *    directly from the SDK for types that are truly provider-specific
+ *
+ * Import convention:
+ *   import { Content, Part, FunctionDeclaration } from '../types/delta.js';
+ *   // NOT from '@google/genai'
+ */
+
+// ---------------------------------------------------------------------------
+// Re-exports — same names, new path. Migration is just import path changes.
+// ---------------------------------------------------------------------------
+
+// Message types
+export {
+  Content,
+  Part,
+  type PartListUnion,
+  type PartUnion,
+} from '@google/genai';
+
+// Request/Response types
+export {
+  GenerateContentResponse,
+  GenerateContentParameters,
+  GenerateContentConfig,
+  type GenerateContentResponseUsageMetadata,
+} from '@google/genai';
+
+// Token counting
+export {
+  type CountTokensResponse,
+  type CountTokensParameters,
+} from '@google/genai';
+
+// Embedding
+export {
+  type EmbedContentResponse,
+  type EmbedContentParameters,
+} from '@google/genai';
+
+// Tool/Function types
+export {
+  FunctionDeclaration,
+  FunctionCall,
+  type FunctionResponse,
+  type Tool,
+  type CallableTool,
+  type ToolListUnion,
+} from '@google/genai';
+
+// Schema types
+export {
+  type Schema,
+  type SchemaUnion,
+  Type,
+} from '@google/genai';
+
+// Enums
+export {
+  FinishReason,
+} from '@google/genai';
+
+// ---------------------------------------------------------------------------
+// Native Delta types — for features not in @google/genai
+// ---------------------------------------------------------------------------
+
+/** Provider-agnostic model capability descriptor. */
+export interface DeltaModelCapabilities {
+  toolCalling: boolean | null;
+  vision: boolean | null;
+  streaming: boolean | null;
+  contextWindow: number | null;
+  thinkBlocks: boolean | null;
+}
+
+/** Provider identification for schema normalization, diagnostics, etc. */
+export type DeltaProviderType =
+  | 'google'
+  | 'openai'
+  | 'anthropic'
+  | 'bedrock'
+  | 'vertex-ai'
+  | 'openai-compatible'
+  | 'ollama'
+  | 'lmstudio';
diff --git a/packages/core/src/utils/editCorrector.ts b/packages/core/src/utils/editCorrector.ts
index f247f6d30b4..3a9be6cbb75 100644
--- a/packages/core/src/utils/editCorrector.ts
+++ b/packages/core/src/utils/editCorrector.ts
@@ -4,7 +4,10 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { Content, GenerateContentConfig } from '@google/genai';
+import {
+  Content,
+  GenerateContentConfig,
+} from '../types/delta.js';
 import { DeltaClient } from '../core/client.js';
 import { EditToolParams, EditTool } from '../tools/edit.js';
 import { WriteFileTool } from '../tools/write-file.js';
diff --git a/packages/core/src/utils/environmentContext.ts b/packages/core/src/utils/environmentContext.ts
index 9cacf924410..d7cfd36acbe 100644
--- a/packages/core/src/utils/environmentContext.ts
+++ b/packages/core/src/utils/environmentContext.ts
@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { Part } from '@google/genai';
+import {
+  Part,
+} from '../types/delta.js';
 import { Config } from '../config/config.js';
 import { getFolderStructure } from './getFolderStructure.js';
 
diff --git a/packages/core/src/utils/errorReporting.ts b/packages/core/src/utils/errorReporting.ts
index 05fc7400ccc..ce1dfc309d0 100644
--- a/packages/core/src/utils/errorReporting.ts
+++ b/packages/core/src/utils/errorReporting.ts
@@ -4,10 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  Content,
+} from '../types/delta.js';
 import fs from 'node:fs/promises';
 import os from 'node:os';
 import path from 'node:path';
-import { Content } from '@google/genai';
 
 interface ErrorReportData {
   error: { message: string; stack?: string } | { message: string };
diff --git a/packages/core/src/utils/fileUtils.ts b/packages/core/src/utils/fileUtils.ts
index 92186e4f8cd..88ce7ee07af 100644
--- a/packages/core/src/utils/fileUtils.ts
+++ b/packages/core/src/utils/fileUtils.ts
@@ -4,9 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {
+  PartUnion,
+} from '../types/delta.js';
 import fs from 'node:fs';
 import path from 'node:path';
-import { PartUnion } from '@google/genai';
+
 import mime from 'mime-types';
 
 // Constants for text file processing
diff --git a/packages/core/src/utils/generateContentResponseUtilities.ts b/packages/core/src/utils/generateContentResponseUtilities.ts
index c5125753a9b..d4150b649ee 100644
--- a/packages/core/src/utils/generateContentResponseUtilities.ts
+++ b/packages/core/src/utils/generateContentResponseUtilities.ts
@@ -4,8 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { GenerateContentResponse, Part, FunctionCall } from '@google/genai';
-
+import {
+  GenerateContentResponse,
+  Part,
+  FunctionCall,
+} from '../types/delta.js';
 export function getResponseText(
   response: GenerateContentResponse,
 ): string | undefined {
diff --git a/packages/core/src/utils/messageInspectors.ts b/packages/core/src/utils/messageInspectors.ts
index 5ef06d7988a..9ac9af562c9 100644
--- a/packages/core/src/utils/messageInspectors.ts
+++ b/packages/core/src/utils/messageInspectors.ts
@@ -4,8 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { Content } from '@google/genai';
-
+import {
+  Content,
+} from '../types/delta.js';
 export function isFunctionResponse(content: Content): boolean {
   return (
     content.role === 'user' &&
diff --git a/packages/core/src/utils/nextSpeakerChecker.ts b/packages/core/src/utils/nextSpeakerChecker.ts
index c5170fa021b..12d513dede2 100644
--- a/packages/core/src/utils/nextSpeakerChecker.ts
+++ b/packages/core/src/utils/nextSpeakerChecker.ts
@@ -4,7 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { Content } from '@google/genai';
+import {
+  Content,
+} from '../types/delta.js';
 import { DeltaClient } from '../core/client.js';
 import { DeltaChat } from '../core/deltaChat.js';
 import { isFunctionResponse } from './messageInspectors.js';
diff --git a/packages/core/src/utils/partUtils.ts b/packages/core/src/utils/partUtils.ts
index c6bf098dc88..af8119118c2 100644
--- a/packages/core/src/utils/partUtils.ts
+++ b/packages/core/src/utils/partUtils.ts
@@ -4,12 +4,15 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { GenerateContentResponse, PartListUnion, Part } from '@google/genai';
-
 /**
  * Converts a PartListUnion into a string.
  * If verbose is true, includes summary representations of non-text parts.
  */
+import {
+  GenerateContentResponse,
+  PartListUnion,
+  Part,
+} from '../types/delta.js';
 export function partToString(
   value: PartListUnion,
   options?: { verbose?: boolean },
diff --git a/packages/core/src/utils/summarizer.ts b/packages/core/src/utils/summarizer.ts
index f188402e9d2..187b954c5b6 100644
--- a/packages/core/src/utils/summarizer.ts
+++ b/packages/core/src/utils/summarizer.ts
@@ -4,12 +4,13 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { ToolResult } from '../tools/tools.js';
 import {
   Content,
   GenerateContentConfig,
   GenerateContentResponse,
-} from '@google/genai';
+} from '../types/delta.js';
+import { ToolResult } from '../tools/tools.js';
+
 import { DeltaClient } from '../core/client.js';
 import { DEFAULT_GEMINI_FLASH_LITE_MODEL } from '../config/models.js';
 import { getResponseText, partToString } from './partUtils.js';