diff --git a/packages/ai/scripts/generate-models.ts b/packages/ai/scripts/generate-models.ts
index d3b9c8f1..eed8b04f 100644
--- a/packages/ai/scripts/generate-models.ts
+++ b/packages/ai/scripts/generate-models.ts
@@ -482,6 +482,97 @@ async function generateModels() {
 		});
 	}
 
+	// Add Google Cloud Code Assist models (Gemini CLI / Antigravity)
+	// These use OAuth authentication via Google account, cost is $0 (uses account quota)
+	const CLOUD_CODE_ASSIST_ENDPOINT = "https://cloudcode-pa.googleapis.com";
+	const cloudCodeAssistModels: Model<"google-cloud-code-assist">[] = [
+		{
+			id: "gemini-3-pro-high",
+			name: "Gemini 3 Pro High (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: true,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 1048576,
+			maxTokens: 65535,
+		},
+		{
+			id: "gemini-3-pro-low",
+			name: "Gemini 3 Pro Low (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: true,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 1048576,
+			maxTokens: 65535,
+		},
+		{
+			id: "gemini-3-flash",
+			name: "Gemini 3 Flash (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: false,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 1048576,
+			maxTokens: 65536,
+		},
+		{
+			id: "claude-sonnet-4-5",
+			name: "Claude Sonnet 4.5 (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: false,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 200000,
+			maxTokens: 64000,
+		},
+		{
+			id: "claude-sonnet-4-5-thinking",
+			name: "Claude Sonnet 4.5 Thinking (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: true,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 200000,
+			maxTokens: 64000,
+		},
+		{
+			id: "claude-opus-4-5-thinking",
+			name: "Claude Opus 4.5 Thinking (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: true,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 200000,
+			maxTokens: 64000,
+		},
+		{
+			id: "gpt-oss-120b-medium",
+			name: "GPT-OSS 120B Medium (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: CLOUD_CODE_ASSIST_ENDPOINT,
+			reasoning: false,
+			input: ["text", "image"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 131072,
+			maxTokens: 32768,
+		},
+	];
+	allModels.push(...cloudCodeAssistModels);
+
 	// Group by provider and deduplicate by model ID
 	const providers: Record<string, Record<string, Model<any>>> = {};
 	for (const model of allModels) {
diff --git a/packages/ai/src/index.ts b/packages/ai/src/index.ts
index f9ed0753..4e960daa 100644
--- a/packages/ai/src/index.ts
+++ b/packages/ai/src/index.ts
@@ -2,6 +2,7 @@ export * from "./agent/index.js";
 export * from "./models.js";
 export * from "./providers/anthropic.js";
 export * from "./providers/google.js";
+export * from "./providers/google-cloud-code-assist.js";
 export * from "./providers/openai-completions.js";
 export * from "./providers/openai-responses.js";
 export * from "./stream.js";
diff --git a/packages/ai/src/models.generated.ts b/packages/ai/src/models.generated.ts
index e682aa54..7acfe5a0 100644
--- a/packages/ai/src/models.generated.ts
+++ b/packages/ai/src/models.generated.ts
@@ -6819,4 +6819,125 @@ export const MODELS = {
 			maxTokens: 30000,
 		} satisfies Model<"openai-completions">,
 	},
+	"google-cloud-code-assist": {
+		"gemini-3-pro-high": {
+			id: "gemini-3-pro-high",
+			name: "Gemini 3 Pro High (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: true,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 1048576,
+			maxTokens: 65535,
+		} satisfies Model<"google-cloud-code-assist">,
+		"gemini-3-pro-low": {
+			id: "gemini-3-pro-low",
+			name: "Gemini 3 Pro Low (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: true,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 1048576,
+			maxTokens: 65535,
+		} satisfies Model<"google-cloud-code-assist">,
+		"gemini-3-flash": {
+			id: "gemini-3-flash",
+			name: "Gemini 3 Flash (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: false,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 1048576,
+			maxTokens: 65536,
+		} satisfies Model<"google-cloud-code-assist">,
+		"claude-sonnet-4-5": {
+			id: "claude-sonnet-4-5",
+			name: "Claude Sonnet 4.5 (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: false,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 200000,
+			maxTokens: 64000,
+		} satisfies Model<"google-cloud-code-assist">,
+		"claude-sonnet-4-5-thinking": {
+			id: "claude-sonnet-4-5-thinking",
+			name: "Claude Sonnet 4.5 Thinking (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: true,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 200000,
+			maxTokens: 64000,
+		} satisfies Model<"google-cloud-code-assist">,
+		"claude-opus-4-5-thinking": {
+			id: "claude-opus-4-5-thinking",
+			name: "Claude Opus 4.5 Thinking (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: true,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 200000,
+			maxTokens: 64000,
+		} satisfies Model<"google-cloud-code-assist">,
+		"gpt-oss-120b-medium": {
+			id: "gpt-oss-120b-medium",
+			name: "GPT-OSS 120B Medium (Cloud Code Assist)",
+			api: "google-cloud-code-assist",
+			provider: "google-cloud-code-assist",
+			baseUrl: "https://cloudcode-pa.googleapis.com",
+			reasoning: false,
+			input: ["text", "image"],
+			cost: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+			},
+			contextWindow: 131072,
+			maxTokens: 32768,
+		} satisfies Model<"google-cloud-code-assist">,
+	},
 } as const;
diff --git a/packages/ai/src/providers/google-cloud-code-assist.ts b/packages/ai/src/providers/google-cloud-code-assist.ts
new file mode 100644
index 00000000..dd1de439
--- /dev/null
+++ b/packages/ai/src/providers/google-cloud-code-assist.ts
@@ -0,0 +1,429 @@
+/**
+ * Google Cloud Code Assist provider for Gemini CLI / Antigravity authentication.
+ * Uses the Cloud Code Assist API endpoint to access Gemini and Claude models.
+ */
+
+import type { Content, ThinkingConfig } from "@google/genai";
+import { calculateCost } from "../models.js";
+import type {
+	Api,
+	AssistantMessage,
+	Context,
+	Model,
+	StreamFunction,
+	StreamOptions,
+	TextContent,
+	ThinkingContent,
+	ToolCall,
+} from "../types.js";
+import { AssistantMessageEventStream } from "../utils/event-stream.js";
+import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
+import { convertMessages, convertTools, mapStopReasonString, mapToolChoice } from "./google-shared.js";
+
+export interface GoogleCloudCodeAssistOptions extends StreamOptions {
+	toolChoice?: "auto" | "none" | "any";
+	thinking?: {
+		enabled: boolean;
+		budgetTokens?: number;
+	};
+	projectId?: string;
+}
+
+const ENDPOINT = "https://cloudcode-pa.googleapis.com";
+const HEADERS = {
+	"User-Agent": "google-api-nodejs-client/9.15.1",
+	"X-Goog-Api-Client": "gl-node/22.17.0",
+	"Client-Metadata": "ideType=IDE_UNSPECIFIED,platform=PLATFORM_UNSPECIFIED,pluginType=GEMINI",
+};
+
+// Counter for generating unique tool call IDs
+let toolCallCounter = 0;
+
+interface CloudCodeAssistRequest {
+	project: string;
+	model: string;
+	request: {
+		contents: Content[];
+		systemInstruction?: { parts: { text: string }[] };
+		generationConfig?: {
+			maxOutputTokens?: number;
+			temperature?: number;
+			thinkingConfig?: ThinkingConfig;
+		};
+		tools?: ReturnType<typeof convertTools>;
+		toolConfig?: {
+			functionCallingConfig: {
+				mode: ReturnType<typeof mapToolChoice>;
+			};
+		};
+	};
+	userAgent?: string;
+	requestId?: string;
+}
+
+interface CloudCodeAssistResponseChunk {
+	response?: {
+		candidates?: Array<{
+			content?: {
+				role: string;
+				parts?: Array<{
+					text?: string;
+					thought?: boolean;
+					thoughtSignature?: string;
+					functionCall?: {
+						name: string;
+						args: Record<string, unknown>;
+						id?: string;
+					};
+				}>;
+			};
+			finishReason?: string;
+		}>;
+		usageMetadata?: {
+			promptTokenCount?: number;
+			candidatesTokenCount?: number;
+			thoughtsTokenCount?: number;
+			totalTokenCount?: number;
+			cachedContentTokenCount?: number;
+		};
+		modelVersion?: string;
+		responseId?: string;
+	};
+	traceId?: string;
+}
+
+export const streamGoogleCloudCodeAssist: StreamFunction<"google-cloud-code-assist"> = (
+	model: Model<"google-cloud-code-assist">,
+	context: Context,
+	options?: GoogleCloudCodeAssistOptions,
+): AssistantMessageEventStream => {
+	const stream = new AssistantMessageEventStream();
+
+	(async () => {
+		const output: AssistantMessage = {
+			role: "assistant",
+			content: [],
+			api: "google-cloud-code-assist" as Api,
+			provider: model.provider,
+			model: model.id,
+			usage: {
+				input: 0,
+				output: 0,
+				cacheRead: 0,
+				cacheWrite: 0,
+				totalTokens: 0,
+				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+			},
+			stopReason: "stop",
+			timestamp: Date.now(),
+		};
+
+		try {
+			const apiKey = options?.apiKey;
+			if (!apiKey) {
+				throw new Error("Google Cloud Code Assist requires an OAuth access token");
+			}
+
+			const projectId = options?.projectId;
+			if (!projectId) {
+				throw new Error("Google Cloud Code Assist requires a project ID");
+			}
+
+			const requestBody = buildRequest(model, context, projectId, options);
+			const url = `${ENDPOINT}/v1internal:streamGenerateContent?alt=sse`;
+
+			const response = await fetch(url, {
+				method: "POST",
+				headers: {
+					Authorization: `Bearer ${apiKey}`,
+					"Content-Type": "application/json",
+					Accept: "text/event-stream",
+					...HEADERS,
+				},
+				body: JSON.stringify(requestBody),
+				signal: options?.signal,
+			});
+
+			if (!response.ok) {
+				const errorText = await response.text();
+				throw new Error(`Cloud Code Assist API error (${response.status}): ${errorText}`);
+			}
+
+			if (!response.body) {
+				throw new Error("No response body");
+			}
+
+			stream.push({ type: "start", partial: output });
+
+			let currentBlock: TextContent | ThinkingContent | null = null;
+			const blocks = output.content;
+			const blockIndex = () => blocks.length - 1;
+
+			// Read SSE stream
+			const reader = response.body.getReader();
+			const decoder = new TextDecoder();
+			let buffer = "";
+
+			while (true) {
+				const { done, value } = await reader.read();
+				if (done) break;
+
+				buffer += decoder.decode(value, { stream: true });
+				const lines = buffer.split("\n");
+				buffer = lines.pop() || "";
+
+				for (const line of lines) {
+					if (!line.startsWith("data:")) continue;
+
+					const jsonStr = line.slice(5).trim();
+					if (!jsonStr) continue;
+
+					let chunk: CloudCodeAssistResponseChunk;
+					try {
+						chunk = JSON.parse(jsonStr);
+					} catch {
+						continue;
+					}
+
+					// Unwrap the response
+					const responseData = chunk.response;
+					if (!responseData) continue;
+
+					const candidate = responseData.candidates?.[0];
+					if (candidate?.content?.parts) {
+						for (const part of candidate.content.parts) {
+							if (part.text !== undefined) {
+								const isThinking = part.thought === true;
+								if (
+									!currentBlock ||
+									(isThinking && currentBlock.type !== "thinking") ||
+									(!isThinking && currentBlock.type !== "text")
+								) {
+									if (currentBlock) {
+										if (currentBlock.type === "text") {
+											stream.push({
+												type: "text_end",
+												contentIndex: blocks.length - 1,
+												content: currentBlock.text,
+												partial: output,
+											});
+										} else {
+											stream.push({
+												type: "thinking_end",
+												contentIndex: blockIndex(),
+												content: currentBlock.thinking,
+												partial: output,
+											});
+										}
+									}
+									if (isThinking) {
+										currentBlock = { type: "thinking", thinking: "", thinkingSignature: undefined };
+										output.content.push(currentBlock);
+										stream.push({ type: "thinking_start", contentIndex: blockIndex(), partial: output });
+									} else {
+										currentBlock = { type: "text", text: "" };
+										output.content.push(currentBlock);
+										stream.push({ type: "text_start", contentIndex: blockIndex(), partial: output });
+									}
+								}
+								if (currentBlock.type === "thinking") {
+									currentBlock.thinking += part.text;
+									currentBlock.thinkingSignature = part.thoughtSignature;
+									stream.push({
+										type: "thinking_delta",
+										contentIndex: blockIndex(),
+										delta: part.text,
+										partial: output,
+									});
+								} else {
+									currentBlock.text += part.text;
+									stream.push({
+										type: "text_delta",
+										contentIndex: blockIndex(),
+										delta: part.text,
+										partial: output,
+									});
+								}
+							}
+
+							if (part.functionCall) {
+								if (currentBlock) {
+									if (currentBlock.type === "text") {
+										stream.push({
+											type: "text_end",
+											contentIndex: blockIndex(),
+											content: currentBlock.text,
+											partial: output,
+										});
+									} else {
+										stream.push({
+											type: "thinking_end",
+											contentIndex: blockIndex(),
+											content: currentBlock.thinking,
+											partial: output,
+										});
+									}
+									currentBlock = null;
+								}
+
+								const providedId = part.functionCall.id;
+								const needsNewId =
+									!providedId || output.content.some((b) => b.type === "toolCall" && b.id === providedId);
+								const toolCallId = needsNewId
+									? `${part.functionCall.name}_${Date.now()}_${++toolCallCounter}`
+									: providedId;
+
+								const toolCall: ToolCall = {
+									type: "toolCall",
+									id: toolCallId,
+									name: part.functionCall.name || "",
+									arguments: part.functionCall.args as Record<string, unknown>,
+									...(part.thoughtSignature && { thoughtSignature: part.thoughtSignature }),
+								};
+
+								output.content.push(toolCall);
+								stream.push({ type: "toolcall_start", contentIndex: blockIndex(), partial: output });
+								stream.push({
+									type: "toolcall_delta",
+									contentIndex: blockIndex(),
+									delta: JSON.stringify(toolCall.arguments),
+									partial: output,
+								});
+								stream.push({ type: "toolcall_end", contentIndex: blockIndex(), toolCall, partial: output });
+							}
+						}
+					}
+
+					if (candidate?.finishReason) {
+						output.stopReason = mapStopReasonString(candidate.finishReason);
+						if (output.content.some((b) => b.type === "toolCall")) {
+							output.stopReason = "toolUse";
+						}
+					}
+
+					if (responseData.usageMetadata) {
+						output.usage = {
+							input: responseData.usageMetadata.promptTokenCount || 0,
+							output:
+								(responseData.usageMetadata.candidatesTokenCount || 0) +
+								(responseData.usageMetadata.thoughtsTokenCount || 0),
+							cacheRead: responseData.usageMetadata.cachedContentTokenCount || 0,
+							cacheWrite: 0,
+							totalTokens: responseData.usageMetadata.totalTokenCount || 0,
+							cost: {
+								input: 0,
+								output: 0,
+								cacheRead: 0,
+								cacheWrite: 0,
+								total: 0,
+							},
+						};
+						calculateCost(model, output.usage);
+					}
+				}
+			}
+
+			if (currentBlock) {
+				if (currentBlock.type === "text") {
+					stream.push({
+						type: "text_end",
+						contentIndex: blockIndex(),
+						content: currentBlock.text,
+						partial: output,
+					});
+				} else {
+					stream.push({
+						type: "thinking_end",
+						contentIndex: blockIndex(),
+						content: currentBlock.thinking,
+						partial: output,
+					});
+				}
+			}
+
+			if (options?.signal?.aborted) {
+				throw new Error("Request was aborted");
+			}
+
+			if (output.stopReason === "aborted" || output.stopReason === "error") {
+				throw new Error("An unknown error occurred");
+			}
+
+			stream.push({ type: "done", reason: output.stopReason, message: output });
+			stream.end();
+		} catch (error) {
+			for (const block of output.content) {
+				if ("index" in block) {
+					delete (block as { index?: number }).index;
+				}
+			}
+			output.stopReason = options?.signal?.aborted ? "aborted" : "error";
+			output.errorMessage = error instanceof Error ? error.message : JSON.stringify(error);
+			stream.push({ type: "error", reason: output.stopReason, error: output });
+			stream.end();
+		}
+	})();
+
+	return stream;
+};
+
+function buildRequest(
+	model: Model<"google-cloud-code-assist">,
+	context: Context,
+	projectId: string,
+	options: GoogleCloudCodeAssistOptions = {},
+): CloudCodeAssistRequest {
+	const contents = convertMessages(model, context);
+
+	const generationConfig: CloudCodeAssistRequest["request"]["generationConfig"] = {};
+	if (options.temperature !== undefined) {
+		generationConfig.temperature = options.temperature;
+	}
+	if (options.maxTokens !== undefined) {
+		generationConfig.maxOutputTokens = options.maxTokens;
+	}
+
+	// Thinking config
+	if (options.thinking?.enabled && model.reasoning) {
+		generationConfig.thinkingConfig = {
+			includeThoughts: true,
+		};
+		if (options.thinking.budgetTokens !== undefined) {
+			generationConfig.thinkingConfig.thinkingBudget = options.thinking.budgetTokens;
+		}
+	}
+
+	const request: CloudCodeAssistRequest["request"] = {
+		contents,
+	};
+
+	// System instruction must be object with parts, not plain string
+	if (context.systemPrompt) {
+		request.systemInstruction = {
+			parts: [{ text: sanitizeSurrogates(context.systemPrompt) }],
+		};
+	}
+
+	if (Object.keys(generationConfig).length > 0) {
+		request.generationConfig = generationConfig;
+	}
+
+	if (context.tools && context.tools.length > 0) {
+		request.tools = convertTools(context.tools);
+		if (options.toolChoice) {
+			request.toolConfig = {
+				functionCallingConfig: {
+					mode: mapToolChoice(options.toolChoice),
+				},
+			};
+		}
+	}
+
+	return {
+		project: projectId,
+		model: model.id,
+		request,
+		userAgent: "pi-coding-agent",
+		requestId: `pi-${Date.now()}-${Math.random().toString(36).slice(2, 11)}`,
+	};
+}
diff --git a/packages/ai/src/providers/google-shared.ts b/packages/ai/src/providers/google-shared.ts
new file mode 100644
index 00000000..e4038b81
--- /dev/null
+++ b/packages/ai/src/providers/google-shared.ts
@@ -0,0 +1,203 @@
+/**
+ * Shared utilities for Google Generative AI and Google Cloud Code Assist providers.
+ */
+
+import { type Content, FinishReason, FunctionCallingConfigMode, type Part, type Schema } from "@google/genai";
+import type { Context, ImageContent, Model, StopReason, TextContent, Tool } from "../types.js";
+import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
+import { transformMessages } from "./transorm-messages.js";
+
+type GoogleApiType = "google-generative-ai" | "google-cloud-code-assist";
+
+/**
+ * Convert internal messages to Gemini Content[] format.
+ */
+export function convertMessages<T extends GoogleApiType>(model: Model<T>, context: Context): Content[] {
+	const contents: Content[] = [];
+	const transformedMessages = transformMessages(context.messages, model);
+
+	for (const msg of transformedMessages) {
+		if (msg.role === "user") {
+			if (typeof msg.content === "string") {
+				contents.push({
+					role: "user",
+					parts: [{ text: sanitizeSurrogates(msg.content) }],
+				});
+			} else {
+				const parts: Part[] = msg.content.map((item) => {
+					if (item.type === "text") {
+						return { text: sanitizeSurrogates(item.text) };
+					} else {
+						return {
+							inlineData: {
+								mimeType: item.mimeType,
+								data: item.data,
+							},
+						};
+					}
+				});
+				const filteredParts = !model.input.includes("image") ? parts.filter((p) => p.text !== undefined) : parts;
+				if (filteredParts.length === 0) continue;
+				contents.push({
+					role: "user",
+					parts: filteredParts,
+				});
+			}
+		} else if (msg.role === "assistant") {
+			const parts: Part[] = [];
+
+			for (const block of msg.content) {
+				if (block.type === "text") {
+					parts.push({ text: sanitizeSurrogates(block.text) });
+				} else if (block.type === "thinking") {
+					const thinkingPart: Part = {
+						thought: true,
+						thoughtSignature: block.thinkingSignature,
+						text: sanitizeSurrogates(block.thinking),
+					};
+					parts.push(thinkingPart);
+				} else if (block.type === "toolCall") {
+					const part: Part = {
+						functionCall: {
+							id: block.id,
+							name: block.name,
+							args: block.arguments,
+						},
+					};
+					if (block.thoughtSignature) {
+						part.thoughtSignature = block.thoughtSignature;
+					}
+					parts.push(part);
+				}
+			}
+
+			if (parts.length === 0) continue;
+			contents.push({
+				role: "model",
+				parts,
+			});
+		} else if (msg.role === "toolResult") {
+			// Build parts array with functionResponse and/or images
+			const parts: Part[] = [];
+
+			// Extract text and image content
+			const textContent = msg.content.filter((c): c is TextContent => c.type === "text");
+			const textResult = textContent.map((c) => c.text).join("\n");
+			const imageContent = model.input.includes("image")
+				? msg.content.filter((c): c is ImageContent => c.type === "image")
+				: [];
+
+			// Always add functionResponse with text result (or placeholder if only images)
+			const hasText = textResult.length > 0;
+			const hasImages = imageContent.length > 0;
+
+			// Use "output" key for success, "error" key for errors as per SDK documentation
+			const responseValue = hasText ? sanitizeSurrogates(textResult) : hasImages ? "(see attached image)" : "";
+
+			parts.push({
+				functionResponse: {
+					id: msg.toolCallId,
+					name: msg.toolName,
+					response: msg.isError ? { error: responseValue } : { output: responseValue },
+				},
+			});
+
+			// Add any images as inlineData parts
+			for (const imageBlock of imageContent) {
+				parts.push({
+					inlineData: {
+						mimeType: imageBlock.mimeType,
+						data: imageBlock.data,
+					},
+				});
+			}
+
+			contents.push({
+				role: "user",
+				parts,
+			});
+		}
+	}
+
+	return contents;
+}
+
+/**
+ * Convert tools to Gemini function declarations format.
+ */
+export function convertTools(
+	tools: Tool[],
+): { functionDeclarations: { name: string; description?: string; parameters: Schema }[] }[] | undefined {
+	if (tools.length === 0) return undefined;
+	return [
+		{
+			functionDeclarations: tools.map((tool) => ({
+				name: tool.name,
+				description: tool.description,
+				parameters: tool.parameters as Schema,
+			})),
+		},
+	];
+}
+
+/**
+ * Map tool choice string to Gemini FunctionCallingConfigMode.
+ */
+export function mapToolChoice(choice: string): FunctionCallingConfigMode {
+	switch (choice) {
+		case "auto":
+			return FunctionCallingConfigMode.AUTO;
+		case "none":
+			return FunctionCallingConfigMode.NONE;
+		case "any":
+			return FunctionCallingConfigMode.ANY;
+		default:
+			return FunctionCallingConfigMode.AUTO;
+	}
+}
+
+/**
+ * Map Gemini FinishReason to our StopReason.
+ */
+export function mapStopReason(reason: FinishReason): StopReason {
+	switch (reason) {
+		case FinishReason.STOP:
+			return "stop";
+		case FinishReason.MAX_TOKENS:
+			return "length";
+		case FinishReason.BLOCKLIST:
+		case FinishReason.PROHIBITED_CONTENT:
+		case FinishReason.SPII:
+		case FinishReason.SAFETY:
+		case FinishReason.IMAGE_SAFETY:
+		case FinishReason.IMAGE_PROHIBITED_CONTENT:
+		case FinishReason.IMAGE_RECITATION:
+		case FinishReason.IMAGE_OTHER:
+		case FinishReason.RECITATION:
+		case FinishReason.FINISH_REASON_UNSPECIFIED:
+		case FinishReason.OTHER:
+		case FinishReason.LANGUAGE:
+		case FinishReason.MALFORMED_FUNCTION_CALL:
+		case FinishReason.UNEXPECTED_TOOL_CALL:
+		case FinishReason.NO_IMAGE:
+			return "error";
+		default: {
+			const _exhaustive: never = reason;
+			throw new Error(`Unhandled stop reason: ${_exhaustive}`);
+		}
+	}
+}
+
+/**
+ * Map string finish reason to our StopReason (for raw API responses).
+ */
+export function mapStopReasonString(reason: string): StopReason {
+	switch (reason) {
+		case "STOP":
+			return "stop";
+		case "MAX_TOKENS":
+			return "length";
+		default:
+			return "error";
+	}
+}
diff --git a/packages/ai/src/providers/google.ts b/packages/ai/src/providers/google.ts
index 659dd5b1..25ff0974 100644
--- a/packages/ai/src/providers/google.ts
+++ b/packages/ai/src/providers/google.ts
@@ -1,12 +1,7 @@
 import {
-	type Content,
-	FinishReason,
-	FunctionCallingConfigMode,
 	type GenerateContentConfig,
 	type GenerateContentParameters,
 	GoogleGenAI,
-	type Part,
-	type Schema,
 	type ThinkingConfig,
 	type ThinkingLevel,
 } from "@google/genai";
@@ -15,20 +10,16 @@ import type {
 	Api,
 	AssistantMessage,
 	Context,
-	ImageContent,
 	Model,
-	StopReason,
 	StreamFunction,
 	StreamOptions,
 	TextContent,
 	ThinkingContent,
-	Tool,
 	ToolCall,
 } from "../types.js";
 import { AssistantMessageEventStream } from "../utils/event-stream.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
-
-import { transformMessages } from "./transorm-messages.js";
+import { convertMessages, convertTools, mapStopReason, mapToolChoice } from "./google-shared.js";
 
 export interface GoogleOptions extends StreamOptions {
 	toolChoice?: "auto" | "none" | "any";
@@ -337,169 +328,3 @@ function buildParams(
 
 	return params;
 }
-function convertMessages(model: Model<"google-generative-ai">, context: Context): Content[] {
-	const contents: Content[] = [];
-	const transformedMessages = transformMessages(context.messages, model);
-
-	for (const msg of transformedMessages) {
-		if (msg.role === "user") {
-			if (typeof msg.content === "string") {
-				contents.push({
-					role: "user",
-					parts: [{ text: sanitizeSurrogates(msg.content) }],
-				});
-			} else {
-				const parts: Part[] = msg.content.map((item) => {
-					if (item.type === "text") {
-						return { text: sanitizeSurrogates(item.text) };
-					} else {
-						return {
-							inlineData: {
-								mimeType: item.mimeType,
-								data: item.data,
-							},
-						};
-					}
-				});
-				const filteredParts = !model.input.includes("image") ? parts.filter((p) => p.text !== undefined) : parts;
-				if (filteredParts.length === 0) continue;
-				contents.push({
-					role: "user",
-					parts: filteredParts,
-				});
-			}
-		} else if (msg.role === "assistant") {
-			const parts: Part[] = [];
-
-			for (const block of msg.content) {
-				if (block.type === "text") {
-					parts.push({ text: sanitizeSurrogates(block.text) });
-				} else if (block.type === "thinking") {
-					const thinkingPart: Part = {
-						thought: true,
-						thoughtSignature: block.thinkingSignature,
-						text: sanitizeSurrogates(block.thinking),
-					};
-					parts.push(thinkingPart);
-				} else if (block.type === "toolCall") {
-					const part: Part = {
-						functionCall: {
-							id: block.id,
-							name: block.name,
-							args: block.arguments,
-						},
-					};
-					if (block.thoughtSignature) {
-						part.thoughtSignature = block.thoughtSignature;
-					}
-					parts.push(part);
-				}
-			}
-
-			if (parts.length === 0) continue;
-			contents.push({
-				role: "model",
-				parts,
-			});
-		} else if (msg.role === "toolResult") {
-			// Build parts array with functionResponse and/or images
-			const parts: Part[] = [];
-
-			// Extract text and image content
-			const textContent = msg.content.filter((c): c is TextContent => c.type === "text");
-			const textResult = textContent.map((c) => c.text).join("\n");
-			const imageContent = model.input.includes("image")
-				? msg.content.filter((c): c is ImageContent => c.type === "image")
-				: [];
-
-			// Always add functionResponse with text result (or placeholder if only images)
-			const hasText = textResult.length > 0;
-			const hasImages = imageContent.length > 0;
-
-			// Use "output" key for success, "error" key for errors as per SDK documentation
-			const responseValue = hasText ? sanitizeSurrogates(textResult) : hasImages ? "(see attached image)" : "";
-
-			parts.push({
-				functionResponse: {
-					id: msg.toolCallId,
-					name: msg.toolName,
-					response: msg.isError ? { error: responseValue } : { output: responseValue },
-				},
-			});
-
-			// Add any images as inlineData parts
-			for (const imageBlock of imageContent) {
-				parts.push({
-					inlineData: {
-						mimeType: imageBlock.mimeType,
-						data: imageBlock.data,
-					},
-				});
-			}
-
-			contents.push({
-				role: "user",
-				parts,
-			});
-		}
-	}
-
-	return contents;
-}
-
-function convertTools(
-	tools: Tool[],
-): { functionDeclarations: { name: string; description?: string; parameters: Schema }[] }[] | undefined {
-	if (tools.length === 0) return undefined;
-	return [
-		{
-			functionDeclarations: tools.map((tool) => ({
-				name: tool.name,
-				description: tool.description,
-				parameters: tool.parameters as Schema, // TypeBox generates JSON Schema compatible with SDK Schema type
-			})),
-		},
-	];
-}
-
-function mapToolChoice(choice: string): FunctionCallingConfigMode {
-	switch (choice) {
-		case "auto":
-			return FunctionCallingConfigMode.AUTO;
-		case "none":
-			return FunctionCallingConfigMode.NONE;
-		case "any":
-			return FunctionCallingConfigMode.ANY;
-		default:
-			return FunctionCallingConfigMode.AUTO;
-	}
-}
-
-function mapStopReason(reason: FinishReason): StopReason {
-	switch (reason) {
-		case FinishReason.STOP:
-			return "stop";
-		case FinishReason.MAX_TOKENS:
-			return "length";
-		case FinishReason.BLOCKLIST:
-		case FinishReason.PROHIBITED_CONTENT:
-		case FinishReason.SPII:
-		case FinishReason.SAFETY:
-		case FinishReason.IMAGE_SAFETY:
-		case FinishReason.IMAGE_PROHIBITED_CONTENT:
-		case FinishReason.IMAGE_RECITATION:
-		case FinishReason.IMAGE_OTHER:
-		case FinishReason.RECITATION:
-		case FinishReason.FINISH_REASON_UNSPECIFIED:
-		case FinishReason.OTHER:
-		case FinishReason.LANGUAGE:
-		case FinishReason.MALFORMED_FUNCTION_CALL:
-		case FinishReason.UNEXPECTED_TOOL_CALL:
-		case FinishReason.NO_IMAGE:
-			return "error";
-		default: {
-			const _exhaustive: never = reason;
-			throw new Error(`Unhandled stop reason: ${_exhaustive}`);
-		}
-	}
-}
diff --git a/packages/ai/src/stream.ts b/packages/ai/src/stream.ts
index 667779fb..54cde072 100644
--- a/packages/ai/src/stream.ts
+++ b/packages/ai/src/stream.ts
@@ -2,6 +2,10 @@ import { ThinkingLevel } from "@google/genai";
 import { supportsXhigh } from "./models.js";
 import { type AnthropicOptions, streamAnthropic } from "./providers/anthropic.js";
 import { type GoogleOptions, streamGoogle } from "./providers/google.js";
+import {
+	type GoogleCloudCodeAssistOptions,
+	streamGoogleCloudCodeAssist,
+} from "./providers/google-cloud-code-assist.js";
 import { type OpenAICompletionsOptions, streamOpenAICompletions } from "./providers/openai-completions.js";
 import { type OpenAIResponsesOptions, streamOpenAIResponses } from "./providers/openai-responses.js";
 import type {
@@ -77,6 +81,13 @@ export function stream<TApi extends Api>(
 		case "google-generative-ai":
 			return streamGoogle(model as Model<"google-generative-ai">, context, providerOptions);
 
+		case "google-cloud-code-assist":
+			return streamGoogleCloudCodeAssist(
+				model as Model<"google-cloud-code-assist">,
+				context,
+				providerOptions as GoogleCloudCodeAssistOptions,
+			);
+
 		default: {
 			// This should never be reached if all Api cases are handled
 			const _exhaustive: never = api;
@@ -196,6 +207,29 @@ function mapOptionsForApi<TApi extends Api>(
 			} satisfies GoogleOptions;
 		}
 
+		case "google-cloud-code-assist": {
+			// Cloud Code Assist uses thinking budget tokens like Gemini 2.5
+			if (!options?.reasoning) {
+				return { ...base, thinking: { enabled: false } } satisfies GoogleCloudCodeAssistOptions;
+			}
+
+			const effort = clampReasoning(options.reasoning)!;
+			const budgets: Record<ClampedReasoningEffort, number> = {
+				minimal: 1024,
+				low: 2048,
+				medium: 8192,
+				high: 16384,
+			};
+
+			return {
+				...base,
+				thinking: {
+					enabled: true,
+					budgetTokens: budgets[effort],
+				},
+			} satisfies GoogleCloudCodeAssistOptions;
+		}
+
 		default: {
 			// Exhaustiveness check
 			const _exhaustive: never = model.api;
diff --git a/packages/ai/src/types.ts b/packages/ai/src/types.ts
index 83d1d892..b560efc2 100644
--- a/packages/ai/src/types.ts
+++ b/packages/ai/src/types.ts
@@ -1,18 +1,25 @@
 import type { AnthropicOptions } from "./providers/anthropic.js";
 import type { GoogleOptions } from "./providers/google.js";
+import type { GoogleCloudCodeAssistOptions } from "./providers/google-cloud-code-assist.js";
 import type { OpenAICompletionsOptions } from "./providers/openai-completions.js";
 import type { OpenAIResponsesOptions } from "./providers/openai-responses.js";
 import type { AssistantMessageEventStream } from "./utils/event-stream.js";
 
 export type { AssistantMessageEventStream } from "./utils/event-stream.js";
 
-export type Api = "openai-completions" | "openai-responses" | "anthropic-messages" | "google-generative-ai";
+export type Api =
+	| "openai-completions"
+	| "openai-responses"
+	| "anthropic-messages"
+	| "google-generative-ai"
+	| "google-cloud-code-assist";
 
 export interface ApiOptionsMap {
 	"anthropic-messages": AnthropicOptions;
 	"openai-completions": OpenAICompletionsOptions;
 	"openai-responses": OpenAIResponsesOptions;
 	"google-generative-ai": GoogleOptions;
+	"google-cloud-code-assist": GoogleCloudCodeAssistOptions;
 }
 
 // Compile-time exhaustiveness check - this will fail if ApiOptionsMap doesn't have all KnownApi keys
diff --git a/packages/tui/src/keys.ts b/packages/tui/src/keys.ts
index aca6838a..d82a01ca 100644
--- a/packages/tui/src/keys.ts
+++ b/packages/tui/src/keys.ts
@@ -259,9 +259,16 @@ export function isCtrlE(data: string): boolean {
 /**
  * Check if input matches Ctrl+K (raw byte or Kitty protocol).
  * Ignores lock key bits.
+ * Also checks if first byte is 0x0b for compatibility with terminals
+ * that may send trailing bytes.
  */
 export function isCtrlK(data: string): boolean {
-	return data === RAW.CTRL_K || data === Keys.CTRL_K || matchesKittySequence(data, CODEPOINTS.k, MODIFIERS.ctrl);
+	return (
+		data === RAW.CTRL_K ||
+		(data.length > 0 && data.charCodeAt(0) === 0x0b) ||
+		data === Keys.CTRL_K ||
+		matchesKittySequence(data, CODEPOINTS.k, MODIFIERS.ctrl)
+	);
 }
 
 /**
diff --git a/plan.md b/plan.md
new file mode 100644
index 00000000..8448a3dd
--- /dev/null
+++ b/plan.md
@@ -0,0 +1,312 @@
+# Google Cloud Code Assist Provider Implementation Plan
+
+## Overview
+Add support for Gemini CLI / Antigravity authentication, which uses Google's Cloud Code Assist API (`cloudcode-pa.googleapis.com`) to access Gemini and Claude models through a unified gateway.
+
+## References
+- Antigravity API Spec: https://github.com/NoeFabris/opencode-antigravity-auth/blob/main/docs/ANTIGRAVITY_API_SPEC.md
+- Gemini CLI Auth: https://github.com/jenslys/opencode-gemini-auth
+- Antigravity Auth: https://github.com/NoeFabris/opencode-antigravity-auth
+
+## Key Differences from Standard Google Provider
+1. **Endpoint**: `cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse`
+2. **Auth**: OAuth token (not API key)
+3. **Request format**: Wrapped in `{ project, model, request: {...} }`
+4. **Response format**: Wrapped in `{ response: {...} }` (needs unwrapping)
+5. **Headers**: Requires `User-Agent`, `X-Goog-Api-Client`, `Client-Metadata`
+
+## OAuth Details
+- **Client ID**: `681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com`
+- **Client Secret**: `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`
+- **Redirect URI**: `http://localhost:8085/oauth2callback`
+- **Scopes**: `cloud-platform`, `userinfo.email`, `userinfo.profile`
+- **Token URL**: `https://oauth2.googleapis.com/token`
+- **Auth URL**: `https://accounts.google.com/o/oauth2/v2/auth`
+
+## Available Models
+| Model ID | Type | Context | Output | Reasoning |
+|----------|------|---------|--------|-----------|
+| gemini-3-pro-high | Gemini | 1M | 64K | Yes |
+| gemini-3-pro-low | Gemini | 1M | 64K | Yes |
+| gemini-3-flash | Gemini | 1M | 64K | No |
+| claude-sonnet-4-5 | Claude | 200K | 64K | No |
+| claude-sonnet-4-5-thinking | Claude | 200K | 64K | Yes |
+| claude-opus-4-5-thinking | Claude | 200K | 64K | Yes |
+| gpt-oss-120b-medium | GPT-OSS | 128K | 32K | No |
+
+All models support: text, image, pdf input; text output; cost is $0 (uses Google account quota)
+
+---
+
+## Implementation Steps
+
+### Step 1: Update types.ts
+File: `packages/ai/src/types.ts`
+
+Add new API type:
+```typescript
+export type Api = "openai-completions" | "openai-responses" | "anthropic-messages" | "google-generative-ai" | "google-cloud-code-assist";
+```
+
+### Step 2: Create google-shared.ts
+File: `packages/ai/src/providers/google-shared.ts`
+
+Extract from `google.ts`:
+- `convertMessages()` - convert internal messages to Gemini Content[] format
+- `convertTools()` - convert tools to Gemini function declarations
+- `mapToolChoice()` - map tool choice to Gemini enum
+- `mapStopReason()` - map Gemini finish reason to our stop reason
+- Shared types and imports
+
+Make functions generic to work with both `google-generative-ai` and `google-cloud-code-assist` API types.
+
+### Step 3: Update google.ts
+File: `packages/ai/src/providers/google.ts`
+
+- Import shared functions from `google-shared.ts`
+- Remove extracted functions
+- Keep: `createClient()`, `buildParams()`, `streamGoogle()`
+
+### Step 4: Create google-cloud-code-assist.ts
+File: `packages/ai/src/providers/google-cloud-code-assist.ts`
+
+Implement:
+```typescript
+export interface GoogleCloudCodeAssistOptions extends StreamOptions {
+  toolChoice?: "auto" | "none" | "any";
+  thinking?: {
+    enabled: boolean;
+    budgetTokens?: number;
+  };
+  projectId?: string; // Google Cloud project ID
+}
+
+export const streamGoogleCloudCodeAssist: StreamFunction<"google-cloud-code-assist"> = (
+  model: Model<"google-cloud-code-assist">,
+  context: Context,
+  options?: GoogleCloudCodeAssistOptions,
+): AssistantMessageEventStream => {
+  // Implementation
+};
+```
+
+Key implementation details:
+1. **Build request body**:
+   ```json
+   {
+     "project": "{projectId}",
+     "model": "{modelId}",
+     "request": {
+       "contents": [...],
+       "systemInstruction": { "parts": [{ "text": "..." }] },
+       "generationConfig": { ... },
+       "tools": [...]
+     }
+   }
+   ```
+
+2. **Headers**:
+   ```
+   Authorization: Bearer {accessToken}
+   Content-Type: application/json
+   Accept: text/event-stream
+   User-Agent: google-api-nodejs-client/9.15.1
+   X-Goog-Api-Client: gl-node/22.17.0
+   Client-Metadata: ideType=IDE_UNSPECIFIED,platform=PLATFORM_UNSPECIFIED,pluginType=GEMINI
+   ```
+
+3. **Endpoint**: `https://cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse`
+
+4. **Parse SSE response**:
+   - Each line: `data: {"response": {...}, "traceId": "..."}`
+   - Extract `response` object, which has same structure as standard Gemini response
+   - Handle thinking parts with `thought: true` and `thoughtSignature`
+
+5. **Use shared functions** for message/tool conversion and stop reason mapping
+
+### Step 5: Update stream.ts
+File: `packages/ai/src/stream.ts`
+
+Add case for new provider:
+```typescript
+import { streamGoogleCloudCodeAssist } from "./providers/google-cloud-code-assist.js";
+
+// In the switch/case or if/else chain:
+case "google-cloud-code-assist":
+  return streamGoogleCloudCodeAssist(model, context, {
+    ...options,
+    // map reasoning to thinking config
+  });
+```
+
+### Step 6: Update models.ts
+File: `packages/ai/src/models.ts`
+
+Add to `xhighSupportedModels` if applicable (check if any models support xhigh).
+
+### Step 7: Add models to generate-models.ts
+File: `packages/ai/scripts/generate-models.ts`
+
+Add hardcoded models:
+```typescript
+const googleCloudCodeAssistModels: Model<"google-cloud-code-assist">[] = [
+  {
+    id: "gemini-3-pro-high",
+    provider: "google-cloud-code-assist",
+    api: "google-cloud-code-assist",
+    name: "Gemini 3 Pro High",
+    contextWindow: 1048576,
+    maxOutputTokens: 65535,
+    pricing: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+    input: ["text", "image", "pdf"],
+    output: ["text"],
+    reasoning: true,
+  },
+  // ... other models
+];
+```
+
+### Step 8: Update index.ts exports
+File: `packages/ai/src/index.ts`
+
+Export new provider:
+```typescript
+export { streamGoogleCloudCodeAssist, type GoogleCloudCodeAssistOptions } from "./providers/google-cloud-code-assist.js";
+```
+
+---
+
+## Phase 2: OAuth Flow in coding-agent
+
+### Step 9: Create google-cloud.ts OAuth handler
+File: `packages/coding-agent/src/core/oauth/google-cloud.ts`
+
+Implement:
+```typescript
+import { createHash, randomBytes } from "crypto";
+import { createServer } from "http";
+import { type OAuthCredentials, saveOAuthCredentials } from "./storage.js";
+
+const CLIENT_ID = "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com";
+const CLIENT_SECRET = "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";
+const REDIRECT_URI = "http://localhost:8085/oauth2callback";
+const SCOPES = [
+  "https://www.googleapis.com/auth/cloud-platform",
+  "https://www.googleapis.com/auth/userinfo.email",
+  "https://www.googleapis.com/auth/userinfo.profile",
+];
+const AUTH_URL = "https://accounts.google.com/o/oauth2/v2/auth";
+const TOKEN_URL = "https://oauth2.googleapis.com/token";
+
+export async function loginGoogleCloud(
+  onAuth: (info: { url: string; instructions?: string }) => void,
+  onProgress?: (message: string) => void,
+): Promise<OAuthCredentials & { projectId?: string }> {
+  // 1. Generate PKCE
+  // 2. Start local server on port 8085
+  // 3. Build auth URL and call onAuth
+  // 4. Wait for callback with code
+  // 5. Exchange code for tokens
+  // 6. Discover/provision project via loadCodeAssist endpoint
+  // 7. Return credentials with projectId
+}
+
+export async function refreshGoogleCloudToken(refreshToken: string): Promise<OAuthCredentials> {
+  // Refresh token flow
+}
+
+// Project discovery
+async function discoverProject(accessToken: string): Promise<string> {
+  // Call /v1internal:loadCodeAssist to get project ID
+  // Or /v1internal:onboardUser if needed
+}
+```
+
+### Step 10: Update oauth/index.ts
+File: `packages/coding-agent/src/core/oauth/index.ts`
+
+- Add `"google-cloud"` to `SupportedOAuthProvider`
+- Add to `getOAuthProviders()` list
+- Add case in `login()` function
+- Add case in `refreshToken()` function
+
+### Step 11: Update oauth/storage.ts
+File: `packages/coding-agent/src/core/oauth/storage.ts`
+
+Extend `OAuthCredentials` to include optional `projectId`:
+```typescript
+export interface OAuthCredentials {
+  type: "oauth";
+  refresh: string;
+  access: string;
+  expires: number;
+  enterpriseUrl?: string;
+  projectId?: string;  // For Google Cloud
+}
+```
+
+### Step 12: Update model-config.ts
+File: `packages/coding-agent/src/core/model-config.ts`
+
+Add logic to get API key for `google-cloud-code-assist` provider:
+- Check for OAuth token via `getOAuthToken("google-cloud")`
+- Return the access token as the "API key"
+
+---
+
+## Phase 3: Testing
+
+### Manual Testing
+1. Run `pi` and use `/login` to authenticate with Google
+2. Select a google-cloud-code-assist model
+3. Send a message and verify streaming works
+4. Test tool calling
+5. Test thinking models
+
+### Verification Points
+- [ ] OAuth flow completes successfully
+- [ ] Token refresh works
+- [ ] Streaming text works
+- [ ] Thinking blocks are parsed correctly
+- [ ] Tool calls work
+- [ ] Tool results are sent correctly
+- [ ] Error handling works (rate limits, auth errors)
+
+---
+
+## Notes
+
+### systemInstruction Format
+Must be object with parts, NOT plain string:
+```json
+{
+  "systemInstruction": {
+    "parts": [{ "text": "You are a helpful assistant." }]
+  }
+}
+```
+
+### Tool Name Rules
+- Must start with letter or underscore
+- Allowed: a-zA-Z0-9, underscores, dots, colons, dashes
+- Max 64 chars
+- No slashes or spaces
+
+### Thinking Config
+```json
+{
+  "generationConfig": {
+    "thinkingConfig": {
+      "thinkingBudget": 8000,
+      "includeThoughts": true
+    }
+  }
+}
+```
+
+### Response Unwrapping
+SSE lines come as:
+```
+data: {"response": {...}, "traceId": "..."}
+```
+Need to extract `response` object which matches standard Gemini format.