diff --git a/frontend/src/lib/components/copilot/chatModelSettings.test.ts b/frontend/src/lib/components/copilot/chatModelSettings.test.ts
index 9088bd2405..18927069af 100644
--- a/frontend/src/lib/components/copilot/chatModelSettings.test.ts
+++ b/frontend/src/lib/components/copilot/chatModelSettings.test.ts
@@ -135,6 +135,15 @@ describe('carriedReasoning', () => {
 		expect(carriedReasoning(REASONING_OFF, REASONING_OFF, cap('gpt-5'))).toBeUndefined()
 	})
 
+	// A provider the registry has no rules for draws no thinking control, so a carried level
+	// would be invisible and unclearable — and still sent, since an explicitly set effort
+	// goes out whatever the model.
+	it('drops the effort where it has no rules for the provider', () => {
+		expect(
+			carriedReasoning('high', REASONING_OFF, getReasoningCapability('customai', 'deepseek-r1'))
+		).toBeUndefined()
+	})
+
 	it('has nothing to carry when no effort is set', () => {
 		expect(carriedReasoning(undefined, '', cap('gpt-5.1'))).toBeUndefined()
 		expect(carriedReasoning('', '', cap('gpt-5.1'))).toBeUndefined()
diff --git a/frontend/src/lib/components/copilot/chatModelSettings.ts b/frontend/src/lib/components/copilot/chatModelSettings.ts
index 0dda8d0e2f..bbe6111270 100644
--- a/frontend/src/lib/components/copilot/chatModelSettings.ts
+++ b/frontend/src/lib/components/copilot/chatModelSettings.ts
@@ -85,17 +85,18 @@ export const REASONING_PROVIDER_DEFAULT = 'default'
  * rejects the request or quietly runs at another one, and the button would name a level the
  * run never used. Off survives only onto a model that can truly disable.
  *
- * A model the registry has no rules for keeps whatever it had: dropping on `supported:
- * false` would discard a real setting on the strength of never having heard of the
- * provider, and nothing would draw a control to put it back.
+ * A model the registry has no rules for drops it too, for the same reason: the button draws
+ * no thinking control there, so a carried level would be invisible and unclearable while
+ * still going out on the wire — `resolveEffectiveReasoning` sends an explicitly set effort
+ * whatever the model, and a provider that rejects the field would then fail every turn with
+ * nothing on screen to explain it.
  */
 export function carriedReasoning(
 	current: string | undefined,
 	offToken: string | undefined,
-	capability: { levels: string[]; canDisable: boolean; known: boolean }
+	capability: { levels: string[]; canDisable: boolean }
 ): string | undefined {
 	if (current === undefined || current === '') return undefined
-	if (!capability.known) return current
 	if (offToken !== undefined && current === offToken) {
 		return capability.canDisable ? current : undefined
 	}