diff --git a/Cargo.lock b/Cargo.lock
index f263072..5ac156f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -226,7 +226,7 @@ checksum = "8ae3f5d315924270530207e2a68396c3cc547f6dca3fbdca317cfb1a51edb593"
 
 [[package]]
 name = "cassady"
-version = "0.3.3"
+version = "0.3.4"
 dependencies = [
  "anyhow",
  "async-trait",
diff --git a/Cargo.toml b/Cargo.toml
index 3b90bd2..aa7bad1 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "cassady"
-version = "0.3.3"
+version = "0.3.4"
 edition = "2021"
 description = "Cassady/Cass minimal terminal coding agent"
 license = "MIT"
diff --git a/src/providers/chatgpt_codex.rs b/src/providers/chatgpt_codex.rs
index cf6c6bd..a9f058d 100644
--- a/src/providers/chatgpt_codex.rs
+++ b/src/providers/chatgpt_codex.rs
@@ -197,6 +197,8 @@ fn responses_body(
         body["reasoning"] = json!({"effort": "minimal", "summary": "auto"});
     } else if let Some(effort) = reasoning_effort.request_value() {
         body["reasoning"] = json!({"effort": effort, "summary": "auto"});
+    } else if reasoning_effort == ReasoningEffort::Off {
+        body["reasoning"] = json!({"effort": "none", "summary": "auto"});
     }
     body
 }
@@ -504,6 +506,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn responses_body_sends_none_effort_when_reasoning_is_off() {
+        let body = responses_body(
+            "gpt-test",
+            vec![ModelMessage::User {
+                content: "hello".into(),
+            }],
+            Vec::new(),
+            ReasoningEffort::Off,
+            false,
+        );
+
+        assert_eq!(
+            body["reasoning"],
+            json!({"effort": "none", "summary": "auto"})
+        );
+    }
+
     #[test]
     fn stream_parser_collects_text_and_function_call() {
         let (tx, _rx) = mpsc::unbounded_channel();
diff --git a/src/providers/mod.rs b/src/providers/mod.rs
index 1f67008..b3b926f 100644
--- a/src/providers/mod.rs
+++ b/src/providers/mod.rs
@@ -28,11 +28,13 @@ impl ProviderClient {
         match config.active_provider.kind.as_str() {
             DEFAULT_PROVIDER_KIND => {
                 let api_key = config.resolved_api_key()?;
-                let reasoning_request_format = config
-                    .model_metadata
-                    .as_ref()
+                let model_metadata = config.model_metadata.as_ref();
+                let reasoning_request_format = model_metadata
                     .map(|model| model.reasoning.request_format)
                     .unwrap_or_default();
+                let reasoning_supported = model_metadata
+                    .map(|model| model.reasoning.supported)
+                    .unwrap_or(false);
                 Ok(Self::OpenAiCompatible(OpenAiCompatibleProvider::new(
                     OpenAiCompatibleSettings {
                         model: config.model.clone(),
@@ -40,6 +42,7 @@ impl ProviderClient {
                         api_key,
                         reasoning_effort: options.reasoning_effort,
                         reasoning_request_format,
+                        reasoning_supported,
                     },
                 )))
             }
diff --git a/src/providers/openai_compatible.rs b/src/providers/openai_compatible.rs
index 9d8341f..3d0f714 100644
--- a/src/providers/openai_compatible.rs
+++ b/src/providers/openai_compatible.rs
@@ -18,6 +18,7 @@ pub struct OpenAiCompatibleProvider {
     api_key: String,
     reasoning_effort: ReasoningEffort,
     reasoning_request_format: ReasoningRequestFormat,
+    reasoning_supported: bool,
 }
 
 #[derive(Debug, Clone)]
@@ -27,6 +28,7 @@ pub struct OpenAiCompatibleSettings {
     pub api_key: String,
     pub reasoning_effort: ReasoningEffort,
     pub reasoning_request_format: ReasoningRequestFormat,
+    pub reasoning_supported: bool,
 }
 
 #[derive(Debug, Default)]
@@ -45,6 +47,7 @@ impl OpenAiCompatibleProvider {
             api_key: settings.api_key,
             reasoning_effort: settings.reasoning_effort,
             reasoning_request_format: settings.reasoning_request_format,
+            reasoning_supported: settings.reasoning_supported,
         }
     }
 
@@ -65,6 +68,7 @@ impl OpenAiCompatibleProvider {
             &mut body,
             self.reasoning_effort,
             self.reasoning_request_format,
+            self.reasoning_supported,
         );
         let resp = self
             .client
@@ -219,9 +223,17 @@ fn apply_reasoning_request(
     body: &mut Value,
     effort: ReasoningEffort,
     format: ReasoningRequestFormat,
+    supported: bool,
 ) {
-    let Some(effort) = effort.request_value() else {
+    if !supported {
         return;
+    }
+    let effort_str = match effort {
+        ReasoningEffort::Off => "none",
+        _ => match effort.request_value() {
+            Some(value) => value,
+            None => return,
+        },
     };
     let Value::Object(obj) = body else {
         return;
@@ -230,11 +242,11 @@ fn apply_reasoning_request(
         ReasoningRequestFormat::ReasoningEffort => {
             obj.insert(
                 "reasoning_effort".to_string(),
-                Value::String(effort.to_string()),
+                Value::String(effort_str.to_string()),
             );
         }
         ReasoningRequestFormat::ReasoningObject => {
-            obj.insert("reasoning".to_string(), json!({ "effort": effort }));
+            obj.insert("reasoning".to_string(), json!({ "effort": effort_str }));
         }
     }
 }
@@ -316,3 +328,60 @@ fn chat_url(base: &str) -> String {
         format!("{}/chat/completions", base.trim_end_matches('/'))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn reasoning_effort_format_sends_none_when_off_and_supported() {
+        let mut body = json!({"model": "test"});
+        apply_reasoning_request(
+            &mut body,
+            ReasoningEffort::Off,
+            ReasoningRequestFormat::ReasoningEffort,
+            true,
+        );
+        assert_eq!(
+            body["reasoning_effort"],
+            Value::String("none".to_string())
+        );
+    }
+
+    #[test]
+    fn reasoning_object_format_sends_none_when_off_and_supported() {
+        let mut body = json!({"model": "test"});
+        apply_reasoning_request(
+            &mut body,
+            ReasoningEffort::Off,
+            ReasoningRequestFormat::ReasoningObject,
+            true,
+        );
+        assert_eq!(body["reasoning"], json!({ "effort": "none" }));
+    }
+
+    #[test]
+    fn reasoning_sends_nothing_when_unsupported_even_if_off() {
+        let mut body = json!({"model": "test"});
+        apply_reasoning_request(
+            &mut body,
+            ReasoningEffort::Off,
+            ReasoningRequestFormat::ReasoningEffort,
+            false,
+        );
+        assert!(body.get("reasoning_effort").is_none());
+        assert!(body.get("reasoning").is_none());
+    }
+
+    #[test]
+    fn reasoning_sends_nothing_when_unsupported_even_if_high() {
+        let mut body = json!({"model": "test"});
+        apply_reasoning_request(
+            &mut body,
+            ReasoningEffort::High,
+            ReasoningRequestFormat::ReasoningObject,
+            false,
+        );
+        assert!(body.get("reasoning").is_none());
+    }
+}