diff --git a/docs/guides/providers.md b/docs/guides/providers.md
index d99d8c016..0bc2a79ce 100644
--- a/docs/guides/providers.md
+++ b/docs/guides/providers.md
@@ -293,6 +293,31 @@ For direct Anthropic API access or custom endpoints that only support Anthropic'
 `api_base` defaults to `http://localhost:1234/v1`. API key is optional unless your LM Studio server enables authentication.<br/>
 With explicit `provider`, PicoClaw sends `openai/gpt-oss-20b` unchanged to the LM Studio server. The legacy compatibility form `"model": "lmstudio/openai/gpt-oss-20b"` still resolves to the same upstream model ID when `provider` is omitted.
 
+**OpenRouter reasoning models (suppressing thinking output)**
+
+Some OpenRouter reasoning models (for example `nvidia/nemotron-3-super-120b-a12b:free`) emit their chain-of-thought into `message.content` rather than a separate reasoning channel. With a strict prompt like `Reply with exactly: PONG`, the visible reply may then start with reasoning preamble such as `We need to ...` before the requested text.
+
+Pass `extra_body.reasoning.exclude = true` so OpenRouter strips the reasoning server-side:
+
+```json
+{
+  "model_name": "openrouter-nemotron-free",
+  "provider": "openrouter",
+  "model": "nvidia/nemotron-3-super-120b-a12b:free",
+  "api_base": "https://openrouter.ai/api/v1",
+  "api_keys": ["sk-or-v1-..."],
+  "extra_body": {
+    "reasoning": {
+      "exclude": true
+    }
+  }
+}
+```
+
+This is shipped as a default `model_list` entry (`openrouter-nemotron-free`); add your `api_keys` to enable it.
+
+Tradeoff: only set this on entries that should hide reasoning. If you rely on OpenRouter to surface reasoning tokens (for example to render thinking separately), leave `extra_body` unset on those models. PicoClaw does not auto-inject `reasoning.exclude` for OpenRouter, since reasoning visibility is a per-model preference.
+
 **Custom Proxy/API**
 
 ```json
diff --git a/docs/operations/troubleshooting.md b/docs/operations/troubleshooting.md
index 16229f369..98ae9a4a7 100644
--- a/docs/operations/troubleshooting.md
+++ b/docs/operations/troubleshooting.md
@@ -48,3 +48,30 @@ Example snippet:
 ```
 
 Get your key at [OpenRouter Keys](https://openrouter.ai/keys).
+
+## OpenRouter reasoning model leaks thinking into reply
+
+**Symptom:** With an OpenRouter reasoning model (for example `nvidia/nemotron-3-super-120b-a12b:free`), even a strict prompt like `Reply with exactly: PONG` produces a reply whose visible content begins with reasoning preamble such as `We need to follow the instruction ...` before the requested text.
+
+**Cause:** Some OpenRouter reasoning models put their chain-of-thought into `message.content` rather than a separate reasoning channel. Without server-side suppression, that reasoning surfaces as the assistant's visible reply.
+
+**Fix:** Set `extra_body.reasoning.exclude = true` on the model entry so OpenRouter strips reasoning before returning content:
+
+```json
+{
+  "model_name": "openrouter-nemotron-free",
+  "provider": "openrouter",
+  "model": "nvidia/nemotron-3-super-120b-a12b:free",
+  "api_base": "https://openrouter.ai/api/v1",
+  "api_keys": ["sk-or-v1-YOUR_OPENROUTER_KEY"],
+  "extra_body": {
+    "reasoning": {
+      "exclude": true
+    }
+  }
+}
+```
+
+PicoClaw ships this as a default `model_list` entry (`openrouter-nemotron-free`); set `api_keys` to use it.
+
+**Tradeoff:** apply this per-model, not globally. Some users want OpenRouter to return reasoning tokens (for example to render thinking separately), so PicoClaw does not auto-inject `reasoning.exclude` for all OpenRouter models.
diff --git a/pkg/config/config_test.go b/pkg/config/config_test.go
index d455572eb..06c3d1c65 100644
--- a/pkg/config/config_test.go
+++ b/pkg/config/config_test.go
@@ -2019,6 +2019,53 @@ func TestDefaultConfig_MinimaxExtraBody(t *testing.T) {
 	}
 }
 
+// TestDefaultConfig_OpenRouterNemotronReasoningExcluded verifies the default
+// OpenRouter Nemotron entry ships with reasoning suppression so reasoning
+// preamble does not leak into visible assistant content.
+func TestDefaultConfig_OpenRouterNemotronReasoningExcluded(t *testing.T) {
+	cfg := DefaultConfig()
+
+	var nemo *ModelConfig
+	for i := range cfg.ModelList {
+		if cfg.ModelList[i].Provider == "openrouter" &&
+			cfg.ModelList[i].Model == "nvidia/nemotron-3-super-120b-a12b:free" {
+			nemo = cfg.ModelList[i]
+			break
+		}
+	}
+	if nemo == nil {
+		t.Fatal("OpenRouter Nemotron model not found in ModelList")
+	}
+	if nemo.ExtraBody == nil {
+		t.Fatal("OpenRouter Nemotron ExtraBody should not be nil")
+	}
+	reasoning, ok := nemo.ExtraBody["reasoning"].(map[string]any)
+	if !ok {
+		t.Fatalf("ExtraBody[reasoning] = %T, want map[string]any", nemo.ExtraBody["reasoning"])
+	}
+	if got, ok := reasoning["exclude"]; !ok || got != true {
+		t.Fatalf("ExtraBody[reasoning][exclude] = %v, want true", got)
+	}
+
+	// Round-trip the model entry through JSON to confirm the nested
+	// reasoning map survives marshal/unmarshal the same way config files do.
+	data, err := json.Marshal(nemo)
+	if err != nil {
+		t.Fatalf("json.Marshal: %v", err)
+	}
+	var rt ModelConfig
+	if err := json.Unmarshal(data, &rt); err != nil {
+		t.Fatalf("json.Unmarshal: %v", err)
+	}
+	rtReasoning, ok := rt.ExtraBody["reasoning"].(map[string]any)
+	if !ok {
+		t.Fatalf("round-tripped ExtraBody[reasoning] = %T, want map[string]any", rt.ExtraBody["reasoning"])
+	}
+	if got, ok := rtReasoning["exclude"]; !ok || got != true {
+		t.Fatalf("round-tripped ExtraBody[reasoning][exclude] = %v, want true", got)
+	}
+}
+
 func TestFilterSensitiveData(t *testing.T) {
 	// Test with nil security config
 	cfg := &Config{}
diff --git a/pkg/config/defaults.go b/pkg/config/defaults.go
index be8c32495..3be234d14 100644
--- a/pkg/config/defaults.go
+++ b/pkg/config/defaults.go
@@ -144,6 +144,20 @@ func DefaultConfig() *Config {
 				Model:     "openai/gpt-5.4",
 				APIBase:   "https://openrouter.ai/api/v1",
 			},
+			// OpenRouter reasoning models that emit thinking into message.content
+			// require server-side reasoning suppression to avoid leaking the
+			// chain-of-thought into the visible assistant reply. See
+			// docs/operations/troubleshooting.md ("OpenRouter reasoning model
+			// leaks thinking into reply").
+			{
+				ModelName: "openrouter-nemotron-free",
+				Provider:  "openrouter",
+				Model:     "nvidia/nemotron-3-super-120b-a12b:free",
+				APIBase:   "https://openrouter.ai/api/v1",
+				ExtraBody: map[string]any{
+					"reasoning": map[string]any{"exclude": true},
+				},
+			},
 
 			// NVIDIA - https://build.nvidia.com/
 			{