diff --git a/codex-rs/core-skills/src/render.rs b/codex-rs/core-skills/src/render.rs
index 1477a299b6..e46ee3f026 100644
--- a/codex-rs/core-skills/src/render.rs
+++ b/codex-rs/core-skills/src/render.rs
@@ -60,6 +60,26 @@ pub const SKILLS_HOW_TO_USE_WITH_ALIASES: &str = r###"- Discovery: The list abov
 - Safety and fallback: If a skill can't be applied cleanly (missing files, unclear instructions), state the issue, pick the next-best approach, and continue."###;
 
 pub fn render_available_skills_body(skill_root_lines: &[String], skill_lines: &[String]) -> String {
+    render_skills_body(skill_root_lines, skill_lines, None)
+}
+
+pub fn render_legacy_available_skills_body(
+    skill_root_lines: &[String],
+    skill_lines: &[String],
+) -> String {
+    let how_to_use = if skill_root_lines.is_empty() {
+        SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS
+    } else {
+        SKILLS_HOW_TO_USE_WITH_ALIASES
+    };
+    render_skills_body(skill_root_lines, skill_lines, Some(how_to_use))
+}
+
+fn render_skills_body(
+    skill_root_lines: &[String],
+    skill_lines: &[String],
+    how_to_use: Option<&str>,
+) -> String {
     let mut lines: Vec<String> = Vec::new();
     lines.push("## Skills".to_string());
     if skill_root_lines.is_empty() {
@@ -72,13 +92,10 @@ pub fn render_available_skills_body(skill_root_lines: &[String], skill_lines: &[
     lines.push("### Available skills".to_string());
     lines.extend(skill_lines.iter().cloned());
 
-    lines.push("### How to use skills".to_string());
-    let how_to_use = if skill_root_lines.is_empty() {
-        SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS
-    } else {
-        SKILLS_HOW_TO_USE_WITH_ALIASES
-    };
-    lines.push(how_to_use.to_string());
+    if let Some(how_to_use) = how_to_use {
+        lines.push("### How to use skills".to_string());
+        lines.push(how_to_use.to_string());
+    }
 
     format!("\n{}\n", lines.join("\n"))
 }
@@ -904,10 +921,10 @@ fn prompt_scope_rank(scope: SkillScope) -> u8 {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use std::collections::HashMap;
     use std::sync::Arc;
 
+    use super::*;
     use codex_utils_absolute_path::test_support::PathBufExt;
     use codex_utils_absolute_path::test_support::test_path_buf;
     use pretty_assertions::assert_eq;
@@ -1203,6 +1220,19 @@ mod tests {
         assert!(rendered_text.contains("- repo-skill:"));
     }
 
+    #[test]
+    fn alias_overhead_uses_catalog_only_prompt() {
+        let roots = vec![format!("- `r0` = `/very/long/{}`", "x".repeat(600))];
+        let budget = SkillMetadataBudget::Tokens(usize::MAX);
+        let empty: &[String] = &[];
+        let expected = budget
+            .cost(&render_available_skills_body(&roots, empty))
+            .saturating_sub(budget.cost(&render_available_skills_body(&[], empty)));
+
+        assert!(expected > 0);
+        assert_eq!(aliased_metadata_overhead_cost(budget, &roots), expected);
+    }
+
     #[test]
     fn outcome_rendering_omits_aliases_when_absolute_plan_has_no_budget_pressure() {
         let root = test_path_buf("/tmp/skills").abs();
diff --git a/codex-rs/core/src/context/available_skills_instructions.rs b/codex-rs/core/src/context/available_skills_instructions.rs
index 4e166d436c..db8175b4de 100644
--- a/codex-rs/core/src/context/available_skills_instructions.rs
+++ b/codex-rs/core/src/context/available_skills_instructions.rs
@@ -1,5 +1,6 @@
 use codex_core_skills::AvailableSkills;
 use codex_core_skills::render_available_skills_body;
+use codex_core_skills::render::render_legacy_available_skills_body;
 use codex_protocol::protocol::SKILLS_INSTRUCTIONS_CLOSE_TAG;
 use codex_protocol::protocol::SKILLS_INSTRUCTIONS_OPEN_TAG;
 
@@ -10,6 +11,7 @@ use super::ContextualUserFragment;
 pub struct AvailableSkillsInstructions {
     skill_root_lines: Vec<String>,
     skill_lines: Vec<String>,
+    include_legacy_usage_instructions: bool,
 }
 
 impl AvailableSkillsInstructions {
@@ -18,15 +20,18 @@ impl AvailableSkillsInstructions {
         Self {
             skill_root_lines: Vec::new(),
             skill_lines,
+            include_legacy_usage_instructions: false,
         }
     }
-}
 
-impl From<AvailableSkills> for AvailableSkillsInstructions {
-    fn from(available_skills: AvailableSkills) -> Self {
+    pub fn from_available_skills(
+        available_skills: AvailableSkills,
+        include_legacy_usage_instructions: bool,
+    ) -> Self {
         Self {
             skill_root_lines: available_skills.skill_root_lines,
             skill_lines: available_skills.skill_lines,
+            include_legacy_usage_instructions,
         }
     }
 }
@@ -45,6 +50,10 @@ impl ContextualUserFragment for AvailableSkillsInstructions {
     }
 
     fn body(&self) -> String {
-        render_available_skills_body(&self.skill_root_lines, &self.skill_lines)
+        if self.include_legacy_usage_instructions {
+            render_legacy_available_skills_body(&self.skill_root_lines, &self.skill_lines)
+        } else {
+            render_available_skills_body(&self.skill_root_lines, &self.skill_lines)
+        }
     }
 }
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 0ecc706818..754eb7324c 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -461,6 +461,13 @@ pub(crate) const SUBMISSION_CHANNEL_CAPACITY: usize = 512;
 const CYBER_VERIFY_URL: &str = "https://chatgpt.com/cyber";
 const CYBER_SAFETY_URL: &str = "https://developers.openai.com/codex/concepts/cyber-safety";
 
+fn model_requires_legacy_skills_instructions(model: &str) -> bool {
+    matches!(
+        model,
+        "gpt-5.5" | "gpt-5.4" | "gpt-5.4-mini" | "gpt-5.3-codex" | "gpt-5.2" | "codex-auto-review"
+    )
+}
+
 impl Codex {
     /// Spawn a new [`Codex`] and initialize the session.
     pub(crate) async fn spawn(args: CodexSpawnArgs) -> CodexResult<CodexSpawnOk> {
@@ -2979,7 +2986,10 @@ impl Session {
             );
             if let Some(available_skills) = available_skills {
                 let warning_message = available_skills.warning_message.clone();
-                let skills_instructions = AvailableSkillsInstructions::from(available_skills);
+                let skills_instructions = AvailableSkillsInstructions::from_available_skills(
+                    available_skills,
+                    model_requires_legacy_skills_instructions(&turn_context.model_info.slug),
+                );
                 if let Some(warning_message) = warning_message {
                     self.send_event_raw(Event {
                         id: String::new(),
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 54e24d49cb..264a1b6aa6 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -1640,6 +1640,10 @@ async fn skills_append_to_developer_message() {
         developer_text.contains("demo: build charts"),
         "expected skill summary: {developer_messages:?}"
     );
+    assert!(
+        developer_text.contains("### How to use skills"),
+        "expected legacy skills guidance for models without model-owned instructions: {developer_messages:?}"
+    );
     let expected_path = normalize_path(skill_dir.join("SKILL.md")).unwrap();
     let expected_path_str = expected_path.to_string_lossy().replace('\\', "/");
     assert!(
diff --git a/codex-rs/ext/skills/tests/skills_extension.rs b/codex-rs/ext/skills/tests/skills_extension.rs
index cd6f46d9c9..b3f948368d 100644
--- a/codex-rs/ext/skills/tests/skills_extension.rs
+++ b/codex-rs/ext/skills/tests/skills_extension.rs
@@ -5,7 +5,6 @@ use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering;
 
 use codex_core_skills::HostSkillsSnapshot;
-use codex_core_skills::SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS;
 use codex_core_skills::SKILLS_INTRO_WITH_ABSOLUTE_PATHS;
 use codex_core_skills::SkillLoadOutcome;
 use codex_core_skills::SkillMetadata;
@@ -116,7 +115,7 @@ async fn installed_extension_uses_host_service_snapshot() -> TestResult {
         .await;
 
     let expected_catalog = format!(
-        "{SKILLS_INSTRUCTIONS_OPEN_TAG}\n## Skills\n{SKILLS_INTRO_WITH_ABSOLUTE_PATHS}\n### Available skills\n- demo: Demo skill. (file: {skill_prompt_path})\n### How to use skills\n{SKILLS_HOW_TO_USE_WITH_ABSOLUTE_PATHS}\n{SKILLS_INSTRUCTIONS_CLOSE_TAG}"
+        "{SKILLS_INSTRUCTIONS_OPEN_TAG}\n## Skills\n{SKILLS_INTRO_WITH_ABSOLUTE_PATHS}\n### Available skills\n- demo: Demo skill. (file: {skill_prompt_path})\n{SKILLS_INSTRUCTIONS_CLOSE_TAG}"
     );
     let expected_skill = format!(
         "<skill>\n<name>demo</name>\n<path>{skill_prompt_path}</path>\n{DEMO_SKILL_CONTENTS}\n</skill>"