diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 326853dd8..85801b32b 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `/login together` always failing with HTTP 400 `model_not_available`: key validation chat-completed against the hardcoded non-serverless model `moonshotai/Kimi-K2.5`, so no valid key could pass. Validation now probes Together's authenticated `/v1/models` listing, matching the model-agnostic approach used by other API-key providers ([#8328](https://github.com/can1357/oh-my-pi/issues/8328)).
+
 ## [17.2.15] - 2026-08-12
 
 ### Fixed
diff --git a/packages/ai/src/registry/together.ts b/packages/ai/src/registry/together.ts
index f6731300e..961dd44f5 100644
--- a/packages/ai/src/registry/together.ts
+++ b/packages/ai/src/registry/together.ts
@@ -8,10 +8,14 @@ export const loginTogether = createApiKeyLogin({
 	promptMessage: "Paste your Together API key",
 	placeholder: "sk-...",
 	validation: {
-		kind: "chat-completions",
+		// Validate against the authenticated models listing, not a chat
+		// completion: Together rejects models that only exist behind a dedicated
+		// endpoint (e.g. `moonshotai/Kimi-K2.5`) with an HTTP 400
+		// `model_not_available`, which failed key validation for every valid key
+		// (issue #8328). The `/v1/models` listing is model-agnostic.
+		kind: "models-endpoint",
 		provider: "together",
-		baseUrl: "https://api.together.xyz/v1",
-		model: "moonshotai/Kimi-K2.5",
+		modelsUrl: "https://api.together.xyz/v1/models",
 	},
 });
 
diff --git a/packages/ai/test/issue-8328-repro.test.ts b/packages/ai/test/issue-8328-repro.test.ts
new file mode 100644
index 000000000..01a18f95c
--- /dev/null
+++ b/packages/ai/test/issue-8328-repro.test.ts
@@ -0,0 +1,60 @@
+import { describe, expect, test, vi } from "bun:test";
+import { loginTogether } from "../src/registry/together";
+import type { FetchImpl } from "../src/types";
+
+// Together's serverless API rejects models that only exist behind a dedicated
+// endpoint (e.g. `moonshotai/Kimi-K2.5`) with an HTTP 400 `model_not_available`
+// error — even when the pasted key is perfectly valid. Login validation must
+// therefore not depend on chat-completing against a specific model; it must
+// probe an authenticated, model-agnostic endpoint. Regression guard for #8328.
+const NON_SERVERLESS_400 = {
+	id: "ovsZQhk-2kFHot",
+	error: {
+		message:
+			"Unable to access non-serverless model moonshotai/Kimi-K2.5. Please visit https://api.together.ai/models/moonshotai/Kimi-K2.5 to create and start a new dedicated endpoint for the model.",
+		type: "invalid_request_error",
+		param: null,
+		code: "model_not_available",
+	},
+};
+
+describe("Together login (#8328)", () => {
+	test("validates a valid key against the models endpoint, not a hardcoded model", async () => {
+		const requests: Array<{ url: string; method: string | undefined }> = [];
+		const fetchMock: FetchImpl = vi.fn(async (input: string | URL | Request, init?: RequestInit) => {
+			const url = String(input);
+			requests.push({ url, method: init?.method });
+			// Simulate Together: chat-completions with a non-serverless model 400s,
+			// while the authenticated models listing succeeds for a valid key.
+			if (url.endsWith("/chat/completions")) {
+				return Response.json(NON_SERVERLESS_400, { status: 400 });
+			}
+			if (url.endsWith("/models")) {
+				return Response.json({ object: "list", data: [] });
+			}
+			return Response.json({ error: "unexpected" }, { status: 500 });
+		});
+
+		const apiKey = await loginTogether({
+			onPrompt: async () => "  together-valid-key  ",
+			fetch: fetchMock,
+		});
+
+		expect(apiKey).toBe("together-valid-key");
+		// The only validation request must be the authenticated models listing.
+		expect(requests).toEqual([{ url: "https://api.together.xyz/v1/models", method: "GET" }]);
+	});
+
+	test("still rejects an invalid key", async () => {
+		const fetchMock: FetchImpl = vi.fn(async () =>
+			Response.json({ error: { message: "Invalid API key provided" } }, { status: 401 }),
+		);
+
+		await expect(
+			loginTogether({
+				onPrompt: async () => "bad-key",
+				fetch: fetchMock,
+			}),
+		).rejects.toThrow("together API key validation failed (401)");
+	});
+});