diff --git a/coworker/providers/anthropic_provider.py b/coworker/providers/anthropic_provider.py
index e01dd33d..0a4ede9c 100644
--- a/coworker/providers/anthropic_provider.py
+++ b/coworker/providers/anthropic_provider.py
@@ -35,6 +35,12 @@ from .capabilities import capabilities_for
 # Required by the Messages API; a ceiling, not a spend target.
 DEFAULT_MAX_TOKENS = 16000
 
+# Extended thinking is ON by default (owner call 2026-07-23: no user-facing setting —
+# most users wouldn't know what a budget is; a per-turn composer control is future work).
+# The provider profile's `thinking_budget` remains a hidden override: a number replaces
+# the default, 0 disables thinking entirely.
+DEFAULT_THINKING_BUDGET = 8192
+
 # Anthropic stop_reason → the engine's OpenAI-shaped finish_reason vocabulary.
 _STOP_REASON_MAP = {
     "end_turn": "stop",
diff --git a/coworker/providers/registry.py b/coworker/providers/registry.py
index ccf13d2a..58aee92b 100644
--- a/coworker/providers/registry.py
+++ b/coworker/providers/registry.py
@@ -106,11 +106,15 @@ def _build_openai(profile: dict[str, Any], secrets: Any) -> ProviderClient:
 def _build_anthropic(profile: dict[str, Any], secrets: Any) -> ProviderClient:
     # Key resolution stays in AnthropicProvider/resolve_api_key (explicit → env → SecretStore),
     # deferred to first call so the provider can be built before a key exists.
+    # thinking_budget: hidden profile override — absent/invalid → the default (ON),
+    # explicit 0 → off (see DEFAULT_THINKING_BUDGET).
+    from .anthropic_provider import DEFAULT_THINKING_BUDGET
+
     api_key = ((profile or {}).get("api_key") or "").strip() or None
     try:
         thinking_budget = int(str((profile or {}).get("thinking_budget") or "").strip())
     except ValueError:
-        thinking_budget = 0
+        thinking_budget = DEFAULT_THINKING_BUDGET
     return AnthropicProvider(
         api_key=api_key, secrets=secrets, thinking_budget=thinking_budget
     )
@@ -225,13 +229,8 @@ DESCRIPTORS: list[ProviderDescriptor] = [
                 secret=True,
                 placeholder="sk-ant-…",
             ),
-            ProviderField(
-                "thinking_budget",
-                "Extended thinking budget (tokens, optional)",
-                required=False,
-                placeholder="e.g. 8192 — blank = off",
-                help="Turns on Claude's extended thinking for every request, with this token budget. The thought process shows in the transcript.",
-            ),
+            # No thinking_budget field (owner call 2026-07-23): extended thinking is
+            # on by default; the profile key stays a hidden override (0 = off).
         ],
         build=_build_anthropic,
         recommended_model="claude-fable-5",
diff --git a/surfaces/gui/e2e/fixtures.ts b/surfaces/gui/e2e/fixtures.ts
index 3aa62025..b8f53743 100644
--- a/surfaces/gui/e2e/fixtures.ts
+++ b/surfaces/gui/e2e/fixtures.ts
@@ -328,7 +328,7 @@ const PROVIDERS = [
   // openai: configured + used (drives the "Last used" sub-line and the status dot).
   { name: "openai", title: "OpenAI", needs_key: true, fields: [{ key: "api_key", label: "OpenAI API key", secret: true, required: true, help: "", placeholder: "sk-…" }], configured: true, values: {}, suggested_models: ["gpt-5.5"], key_set_at: "2026-06-12", last_used_at: Math.floor(Date.now() / 1000) - 7200 },
   // anthropic: configured but never used ("Not used yet").
-  { name: "anthropic", title: "Claude (Anthropic)", needs_key: true, fields: [{ key: "api_key", label: "API key", secret: true, required: true, help: "", placeholder: "sk-…" }, { key: "thinking_budget", label: "Extended thinking budget (tokens, optional)", secret: false, required: false, help: "Turns on Claude's extended thinking for every request.", placeholder: "e.g. 8192 — blank = off" }], configured: true, values: {}, suggested_models: ["claude-opus-4-8"], key_set_at: null, last_used_at: null },
+  { name: "anthropic", title: "Claude (Anthropic)", needs_key: true, fields: [{ key: "api_key", label: "API key", secret: true, required: true, help: "", placeholder: "sk-…" }], configured: true, values: {}, suggested_models: ["claude-opus-4-8"], key_set_at: null, last_used_at: null },
   // zai: an OpenAI-compatible vendor — unconfigured, with a prefilled editable endpoint + blurb.
   { name: "zai", title: "Z AI (GLM)", needs_key: true, blurb: "Uses Z AI's OpenAI-compatible API — the endpoint is prefilled, just add your key.", fields: [{ key: "api_key", label: "Z AI API key", secret: true, required: true, help: "", placeholder: "" }, { key: "base_url", label: "Endpoint", secret: false, required: false, help: "Prefilled with Z AI's international endpoint.", placeholder: "https://api.z.ai/api/paas/v4", default: "https://api.z.ai/api/paas/v4" }], configured: false, values: {}, suggested_models: ["glm-5.2"], key_set_at: null, last_used_at: null },
   // ollama: keyless local provider — "configured" without proving anything runs; the
diff --git a/surfaces/gui/e2e/provider-keys.spec.ts b/surfaces/gui/e2e/provider-keys.spec.ts
index 934e4d2a..55dbda9a 100644
--- a/surfaces/gui/e2e/provider-keys.spec.ts
+++ b/surfaces/gui/e2e/provider-keys.spec.ts
@@ -53,20 +53,21 @@ test("a configured provider's form opens with the saved state, no plaintext key"
   await expect(page.getByTestId("set-field-api_key")).toHaveAttribute("placeholder", "••••••••");
 });
 
-test("non-secret extras blur-save on a configured provider (thinking budget)", async ({
+test("non-secret fields blur-save on a configured provider (ollama endpoint)", async ({
   page,
 }) => {
-  // Owner-hit 2026-07-23: typed a thinking budget, left Settings, value silently never
-  // saved — the Test button was the form's only save path. Blur now saves extras.
+  // Owner-hit 2026-07-23 (as the thinking-budget field, since folded into a default):
+  // the Test button was the form's only save path — typing into a non-secret field and
+  // leaving Settings silently discarded it. Blur now saves.
   await openModels(page);
-  await page.getByTestId("set-provider-anthropic").click();
-  const budget = page.getByTestId("set-field-thinking_budget");
-  await budget.fill("8192");
-  await budget.blur();
-  await expect(page.getByTestId("set-field-saved-thinking_budget")).toBeVisible();
+  await page.getByTestId("set-provider-ollama").click();
+  const endpoint = page.getByTestId("set-field-base_url");
+  await endpoint.fill("http://127.0.0.1:9999");
+  await endpoint.blur();
+  await expect(page.getByTestId("set-field-saved-base_url")).toBeVisible();
 
   // Leave and come back: the value survived (served from the provider's stored values).
   await page.getByTestId("set-back").click();
-  await page.getByTestId("set-provider-anthropic").click();
-  await expect(page.getByTestId("set-field-thinking_budget")).toHaveValue("8192");
+  await page.getByTestId("set-provider-ollama").click();
+  await expect(page.getByTestId("set-field-base_url")).toHaveValue("http://127.0.0.1:9999");
 });
diff --git a/tests/test_anthropic_provider.py b/tests/test_anthropic_provider.py
index c6a5d81d..394032fd 100644
--- a/tests/test_anthropic_provider.py
+++ b/tests/test_anthropic_provider.py
@@ -623,3 +623,14 @@ def test_convert_replays_thinking_blocks_ahead_of_tool_use():
     assistant = msgs[1]["content"]
     assert assistant[0] == {"type": "thinking", "thinking": "plan", "signature": "S"}
     assert assistant[1]["type"] == "tool_use"
+
+
+def test_thinking_defaults_on_with_hidden_profile_override():
+    """No user-facing setting (owner call 2026-07-23): thinking is ON by default; the
+    profile's thinking_budget stays a hidden override, 0 = off."""
+    from coworker.providers.anthropic_provider import DEFAULT_THINKING_BUDGET
+    from coworker.providers.registry import build_provider_client
+
+    assert build_provider_client("anthropic", {}, None).thinking_budget == DEFAULT_THINKING_BUDGET
+    assert build_provider_client("anthropic", {"thinking_budget": "2048"}, None).thinking_budget == 2048
+    assert build_provider_client("anthropic", {"thinking_budget": "0"}, None).thinking_budget == 0
diff --git a/tests/test_server.py b/tests/test_server.py
index 97d5e986..b88c558e 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -769,22 +769,13 @@ def test_google_one_click_paused_but_manual_alive(tmp_path):
 
 
 def test_set_provider_persists_extra_fields(tmp_path):
-    """Non-secret descriptor extras (anthropic thinking_budget) round-trip: saved into the
+    """Non-secret descriptor extras (ollama's endpoint) round-trip: saved into the
     profile, echoed by get_providers for form prefill, cleared by an empty save."""
     manager = SessionManager(workspace=tmp_path, provider=ScriptedProvider([]))
-    assert manager.set_provider(
-        "anthropic", {"api_key": "sk-ant-test", "thinking_budget": "8192"}
-    )["ok"]
+    assert manager.set_provider("ollama", {"base_url": "http://127.0.0.1:9999"})["ok"]
     providers = {p["name"]: p for p in manager.get_providers()}
-    assert providers["anthropic"]["values"]["thinking_budget"] == "8192"
+    assert providers["ollama"]["values"]["base_url"] == "http://127.0.0.1:9999"
 
-    from coworker.providers.registry import build_provider_client
-
-    built = build_provider_client(
-        "anthropic", manager.secrets.get("provider:anthropic"), manager.secrets
-    )
-    assert built.thinking_budget == 8192
-
-    manager.set_provider("anthropic", {"thinking_budget": ""})
+    manager.set_provider("ollama", {"base_url": ""})
     providers = {p["name"]: p for p in manager.get_providers()}
-    assert "thinking_budget" not in providers["anthropic"]["values"]
+    assert "base_url" not in providers["ollama"]["values"]