diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4aebb5a..e38d0d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,9 @@ CalVer image tags (`stable-YYYY.MM.N`, `dev-YYYY.MM.N`) are produced for every C
 
 ## [Unreleased]
 
+### Fixed
+- **Unauthenticated browser requests to `GET /api/initial-workspace.zip` now redirect to `/login?next=/api/initial-workspace.zip` instead of returning a raw JSON 401** (#315). This is the one `/api/*` endpoint that's designed to be hit directly from a browser bookmark (the analyst clean-install zip), so it intentionally opts out of the global `_API_PATH_PREFIXES` "never redirect /api/*" contract in `app/main.py`. CLI / curl / other API clients (any `Accept` without `text/html` — including the `*/*` default) keep getting the 401 they can handle.
+
 ## [0.54.17] — 2026-05-15
 
 ### Changed
diff --git a/app/api/initial_workspace.py b/app/api/initial_workspace.py
index 838763c..1858833 100644
--- a/app/api/initial_workspace.py
+++ b/app/api/initial_workspace.py
@@ -30,11 +30,12 @@ from datetime import datetime, timezone
 from typing import Any, Optional
 
 import duckdb
-from fastapi import APIRouter, Depends, HTTPException, Response
+from fastapi import APIRouter, Depends, HTTPException, Request, Response
+from fastapi.responses import RedirectResponse
 from pydantic import BaseModel
 
 from app.auth.access import require_admin
-from app.auth.dependencies import _get_db, get_current_user
+from app.auth.dependencies import _get_db, get_current_user, get_optional_user
 from app.secrets import persist_overlay_token
 from src.initial_workspace import (
     TemplateValidationError,
@@ -510,7 +511,8 @@ async def analyst_status(
 
 @router.get("/api/initial-workspace.zip")
 async def analyst_zip(
-    user: dict = Depends(get_current_user),
+    request: Request,
+    user: Optional[dict] = Depends(get_optional_user),
     conn: duckdb.DuckDBPyConnection = Depends(_get_db),
 ):
     """Return the zip of the cloned template tree (sans ``.git/``).
@@ -524,6 +526,22 @@ async def analyst_zip(
     this; defense in depth). 503 when configured but never synced — the
     CLI then surfaces a typed error pointing at "Sync now".
     """
+    if user is None:
+        # Browser → redirect to /login (target preserved via ?next=).
+        # CLI / curl / API client → raw 401 they can handle.
+        # This endpoint is the one `/api/*` URL designed to be hit directly
+        # from a browser bookmark (analyst clean-install zip), so it
+        # intentionally opts out of the global `_API_PATH_PREFIXES`
+        # "never redirect /api/*" contract in `app/main.py`. Matching only
+        # `text/html` — NOT `*/*` — mirrors `_wants_html()` in `app/main.py`:
+        # `*/*` is curl's default and must keep getting the raw 401 so
+        # tooling that parses `{"detail": "..."}` doesn't silently break.
+        if "text/html" in request.headers.get("accept", ""):
+            return RedirectResponse(
+                url="/login?next=/api/initial-workspace.zip", status_code=302
+            )
+        raise HTTPException(status_code=401, detail="Missing or invalid Authorization header")
+
     section = _read_section()
     if not section.get("url"):
         raise HTTPException(status_code=404, detail={"kind": "not_configured"})
diff --git a/tests/test_initial_workspace_api.py b/tests/test_initial_workspace_api.py
index 69e627f..ebef314 100644
--- a/tests/test_initial_workspace_api.py
+++ b/tests/test_initial_workspace_api.py
@@ -586,6 +586,50 @@ def test_analyst_status_configured_synced(web_client, fake_remote):
     assert "CLAUDE.md" in body["files"]
 
 
+def test_analyst_zip_browser_unauthenticated_redirects_to_login(web_client):
+    """Unauthenticated browser request (Accept: text/html) redirects to /login."""
+    r = web_client.get(
+        "/api/initial-workspace.zip",
+        headers={"Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"},
+        follow_redirects=False,
+    )
+    assert r.status_code == 302
+    assert r.headers["location"] == "/login?next=/api/initial-workspace.zip"
+
+
+def test_analyst_zip_api_unauthenticated_returns_401(web_client):
+    """Unauthenticated API client (no text/html in Accept) still gets a JSON 401."""
+    r = web_client.get(
+        "/api/initial-workspace.zip",
+        headers={"Accept": "application/json"},
+    )
+    assert r.status_code == 401
+
+
+def test_analyst_zip_curl_default_accept_returns_401(web_client):
+    """`Accept: */*` (curl's default with no `-H`) lands in the 401 branch.
+
+    Mirrors the `_wants_html()` contract in `app/main.py`: `*/*` must NOT
+    silently flip a curl/tooling client to an HTML response — they expect
+    `{"detail": "..."}` and a real 401.
+    """
+    r = web_client.get(
+        "/api/initial-workspace.zip",
+        headers={"Accept": "*/*"},
+    )
+    assert r.status_code == 401
+
+
+def test_analyst_zip_empty_accept_returns_401(web_client):
+    """Empty `Accept` header lands in the 401 branch — same shape as the `*/*`
+    case (no `text/html` substring means: not a browser, give the raw 401)."""
+    r = web_client.get(
+        "/api/initial-workspace.zip",
+        headers={"Accept": ""},
+    )
+    assert r.status_code == 401
+
+
 def test_analyst_zip_404_when_not_configured(web_client):
     """GET /api/initial-workspace.zip returns 404 when no template."""
     headers = _make_user(web_client)