Custom fetch is not supported by the Google Vertex adapter

Error message

Custom fetch is not supported by the Google Vertex adapter

What it means

Error "Custom fetch is not supported by the Google Vertex adapter" thrown in earendil-works/pi.

Source

Thrown at packages/ai/src/api/google-vertex.ts:99

			content: [],
			api: "google-vertex" 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: "pending",
			timestamp: Date.now(),
		};

		try {
			if (options?.fetch && options.fetch !== globalThis.fetch) {
				throw new Error("Custom fetch is not supported by the Google Vertex adapter");
			}
			const apiKey = resolveApiKey(options);
			// Create the client using either a Vertex API key, if provided, or ADC with project and location
			const client = apiKey
				? createClientWithApiKey(model, apiKey, options?.headers)
				: createClient(model, resolveProject(options), resolveLocation(options), options?.headers, options?.env);
			let params = buildParams(model, context, options);
			const nextParams = await options?.onPayload?.(params, model);
			if (nextParams !== undefined) {
				params = nextParams as GenerateContentParameters;
			}
			const googleStream = await retryGoogleRequest(() => client.models.generateContentStream(params), options);

			stream.push({ type: "start", partial: output });
			let currentBlock: TextContent | ThinkingContent | null = null;
			const blocks = output.content;
			const blockIndex = () => blocks.length - 1;
			for await (const chunk of googleStream) {

View on GitHub (pinned to 4af9d21d3b)

Solutions

Use the default fetch; the Google Vertex adapter manages its own transport.

When it happens

Trigger: Thrown at packages/ai/src/api/google-vertex.ts:99 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of earendil-works/pi@4af9d21d3b (2026-08-24). Data as JSON: /api/errors/aa10f97897326d18. Report an issue: GitHub.