diff --git a/src/hooks/init/antigravity.rs b/src/hooks/init/antigravity.rs
index ee1ed1209f..cb406733c5 100644
--- a/src/hooks/init/antigravity.rs
+++ b/src/hooks/init/antigravity.rs
@@ -34,11 +34,184 @@ pub const ANTIGRAVITY_HOOKS_JSON: &str = r#"{
 /// plugin is enabled.
 const ANTIGRAVITY_RULES_FILE: &str = "AGENTS.md";
 
+pub const LEGACY_RULES_REL_PATH: &str = ".agents/rules/antigravity-rtk-rules.md";
+
+const LEGACY_ANTIGRAVITY_RULES_V1: &str = r#"# RTK - Rust Token Killer (Google Antigravity)
+
+**Usage**: Token-optimized CLI proxy for shell commands.
+
+## Rule
+
+Always prefix shell commands with `rtk` to minimize token consumption.
+
+Examples:
+
+```bash
+rtk git status
+rtk cargo test
+rtk ls src/
+rtk grep "pattern" src/
+rtk find "*.rs" .
+rtk docker ps
+rtk gh pr list
+```
+
+## Meta Commands
+
+```bash
+rtk gain              # Show token savings
+rtk gain --history    # Command history with savings
+rtk discover          # Find missed RTK opportunities
+rtk proxy <cmd>       # Run raw (no filtering, for debugging)
+```
+
+## Why
+
+RTK filters and compresses command output before it reaches the LLM context, saving 60-90% tokens on common operations. Always use `rtk <cmd>` instead of raw commands.
+"#;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum LegacyRulesAction {
+    RemovedFile(PathBuf),
+    StrippedSuffix(PathBuf),
+}
+
+/// Detect and migrate legacy `.agents/rules/antigravity-rtk-rules.md` files written
+/// by earlier RTK releases.
+///
+/// - If the file content is solely an awareness text an earlier release wrote, remove it.
+/// - If the file has that awareness text appended after user content following a blank line,
+///   remove only the RTK suffix, keeping the user content byte-identical.
+/// - Leave any other file at that path untouched and print nothing.
+/// - In dry-run mode, report what would be removed/stripped and write nothing.
+pub fn migrate_legacy_rules_at(
+    workspace_root: &Path,
+    ctx: InitContext,
+) -> Result<Option<LegacyRulesAction>> {
+    let legacy_file = workspace_root.join(LEGACY_RULES_REL_PATH);
+    if !legacy_file.is_file() {
+        return Ok(None);
+    }
+
+    let raw = match fs::read_to_string(&legacy_file) {
+        Ok(c) => c,
+        Err(_) => return Ok(None),
+    };
+
+    let normalized = raw.replace("\r\n", "\n");
+    let trimmed = normalized.trim();
+
+    let known_texts = [
+        RTK_AWARENESS_FULL,
+        RTK_AWARENESS_HIGH,
+        RTK_AWARENESS_DEFAULT,
+        LEGACY_ANTIGRAVITY_RULES_V1,
+    ];
+
+    // 1. Exact match: file content is solely an awareness text an earlier release wrote
+    for known in &known_texts {
+        let known_norm = known.replace("\r\n", "\n");
+        if trimmed == known_norm.trim() {
+            if ctx.dry_run {
+                println!(
+                    "[dry-run] would remove legacy rules file: {}",
+                    legacy_file.display()
+                );
+            } else {
+                // nosemgrep: filesystem-deletion -- legacy migration removes only RTK's legacy awareness rules file.
+                fs::remove_file(&legacy_file).with_context(|| {
+                    format!(
+                        "Failed to remove legacy Antigravity rules file: {}",
+                        legacy_file.display()
+                    )
+                })?;
+                if ctx.verbose > 0 {
+                    eprintln!("Removed legacy rules file: {}", legacy_file.display());
+                }
+            }
+            return Ok(Some(LegacyRulesAction::RemovedFile(legacy_file)));
+        }
+    }
+
+    // 2. Suffix removal: awareness text follows user content after a blank line
+    for known in &known_texts {
+        let known_norm = known.replace("\r\n", "\n");
+        let target = format!("\n\n{}", known_norm.trim());
+        if trimmed.ends_with(&target) {
+            let prefix_len = trimmed.len() - target.len();
+            let remaining_trimmed = &trimmed[..prefix_len];
+
+            if remaining_trimmed.trim().is_empty() {
+                if ctx.dry_run {
+                    println!(
+                        "[dry-run] would remove legacy rules file: {}",
+                        legacy_file.display()
+                    );
+                } else {
+                    // nosemgrep: filesystem-deletion -- legacy migration removes only RTK's legacy awareness rules file.
+                    fs::remove_file(&legacy_file).with_context(|| {
+                        format!(
+                            "Failed to remove legacy Antigravity rules file: {}",
+                            legacy_file.display()
+                        )
+                    })?;
+                    if ctx.verbose > 0 {
+                        eprintln!("Removed legacy rules file: {}", legacy_file.display());
+                    }
+                }
+                return Ok(Some(LegacyRulesAction::RemovedFile(legacy_file)));
+            }
+
+            let target_trimmed = known_norm.trim();
+            let crlf_suffix = format!("\r\n\r\n{}", target_trimmed.replace('\n', "\r\n"));
+            let lf_suffix = format!("\n\n{}", target_trimmed);
+
+            let remaining_bytes = if raw.trim_end().ends_with(&crlf_suffix) {
+                let cut_idx = raw.trim_end().len() - crlf_suffix.len();
+                &raw[..cut_idx]
+            } else if raw.trim_end().ends_with(&lf_suffix) {
+                let cut_idx = raw.trim_end().len() - lf_suffix.len();
+                &raw[..cut_idx]
+            } else {
+                remaining_trimmed
+            };
+
+            if ctx.dry_run {
+                println!(
+                    "[dry-run] would remove legacy awareness text from {}",
+                    legacy_file.display()
+                );
+            } else {
+                atomic_write(&legacy_file, remaining_bytes).with_context(|| {
+                    format!(
+                        "Failed to update legacy Antigravity rules file: {}",
+                        legacy_file.display()
+                    )
+                })?;
+                if ctx.verbose > 0 {
+                    eprintln!(
+                        "Removed legacy awareness text from: {}",
+                        legacy_file.display()
+                    );
+                }
+            }
+            return Ok(Some(LegacyRulesAction::StrippedSuffix(legacy_file)));
+        }
+    }
+
+    // 3. Foreign / unrelated file: leave alone and say nothing
+    Ok(None)
+}
+
 pub fn run_antigravity_mode(global: bool, ctx: InitContext) -> Result<()> {
     if global {
         let home = user_dirs::home().context("Could not determine user home directory")?;
         let base_dir = home.join(".gemini/config");
-        run_antigravity_mode_at(&base_dir, true, ctx)
+        run_antigravity_mode_at(&base_dir, true, ctx)?;
+        if let Ok(cwd) = user_dirs::current_dir() {
+            let _ = migrate_legacy_rules_at(&cwd, ctx)?;
+        }
+        Ok(())
     } else {
         let cwd = user_dirs::current_dir().context("Failed to read current directory")?;
         run_antigravity_mode_at(&cwd, false, ctx)
@@ -55,6 +228,12 @@ pub fn run_antigravity_mode_at(base_dir: &Path, global: bool, ctx: InitContext)
         base_dir.join(".agents/plugins/rtk")
     };
 
+    let legacy_action = if !global {
+        migrate_legacy_rules_at(base_dir, ctx)?
+    } else {
+        None
+    };
+
     let plugin_json_path = plugin_dir.join("plugin.json");
     let hooks_json_path = plugin_dir.join("hooks.json");
     // Rules under `rules/` apply whenever the plugin is active, as plain markdown
@@ -114,6 +293,15 @@ pub fn run_antigravity_mode_at(base_dir: &Path, global: bool, ctx: InitContext)
             "  Rules:  rules/{ANTIGRAVITY_RULES_FILE} (awareness level: {})",
             ctx.awareness
         );
+        match legacy_action {
+            Some(LegacyRulesAction::RemovedFile(ref p)) => {
+                println!("  Legacy: removed {}", p.display());
+            }
+            Some(LegacyRulesAction::StrippedSuffix(ref p)) => {
+                println!("  Legacy: removed awareness text from {}", p.display());
+            }
+            None => {}
+        }
         println!("  Restart Antigravity to load the plugin. Test with: git status");
         println!(
             "\n  Note: Antigravity checks permissions after hooks rewrite a command.\n  \
@@ -133,7 +321,21 @@ pub fn uninstall_antigravity_mode(global: bool, ctx: InitContext) -> Result<()>
     } else {
         user_dirs::current_dir().context("Failed to read current directory")?
     };
-    let removed = uninstall_antigravity_mode_at(&base_dir, global, ctx)?;
+    let mut removed = uninstall_antigravity_mode_at(&base_dir, global, ctx)?;
+
+    if global
+        && let Ok(cwd) = user_dirs::current_dir()
+        && let Some(action) = migrate_legacy_rules_at(&cwd, ctx)?
+    {
+        match action {
+            LegacyRulesAction::RemovedFile(p) => {
+                removed.push(format!("legacy rules file: {}", p.display()));
+            }
+            LegacyRulesAction::StrippedSuffix(p) => {
+                removed.push(format!("legacy awareness text in: {}", p.display()));
+            }
+        }
+    }
 
     if removed.is_empty() {
         println!("RTK Antigravity support was not installed (nothing to remove)");
@@ -191,6 +393,17 @@ pub fn uninstall_antigravity_mode_at(
         removed.push(format!("Antigravity plugin: {}", plugin_dir.display()));
     }
 
+    if !global && let Some(action) = migrate_legacy_rules_at(base_dir, ctx)? {
+        match action {
+            LegacyRulesAction::RemovedFile(p) => {
+                removed.push(format!("legacy rules file: {}", p.display()));
+            }
+            LegacyRulesAction::StrippedSuffix(p) => {
+                removed.push(format!("legacy awareness text in: {}", p.display()));
+            }
+        }
+    }
+
     Ok(removed)
 }
 
@@ -337,4 +550,103 @@ mod tests {
         let plugin_dir = temp.path().join(".agents/plugins/rtk");
         assert!(!plugin_dir.exists(), "Plugin dir should be removed");
     }
+
+    #[test]
+    fn test_migrate_legacy_rules_exact_match_removed() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        fs::write(&legacy_file, RTK_AWARENESS_FULL).unwrap();
+
+        let action = migrate_legacy_rules_at(temp.path(), InitContext::default()).unwrap();
+        assert_eq!(
+            action,
+            Some(LegacyRulesAction::RemovedFile(legacy_file.clone()))
+        );
+        assert!(!legacy_file.exists());
+    }
+
+    #[test]
+    fn test_migrate_legacy_rules_exact_match_v1_removed() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        fs::write(&legacy_file, LEGACY_ANTIGRAVITY_RULES_V1).unwrap();
+
+        let action = migrate_legacy_rules_at(temp.path(), InitContext::default()).unwrap();
+        assert_eq!(
+            action,
+            Some(LegacyRulesAction::RemovedFile(legacy_file.clone()))
+        );
+        assert!(!legacy_file.exists());
+    }
+
+    #[test]
+    fn test_migrate_legacy_rules_suffix_stripped() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        let user_content = "# Project Coding Standards\n\nAlways write tests.";
+        let full_content = format!("{user_content}\n\n{}", RTK_AWARENESS_FULL);
+        fs::write(&legacy_file, &full_content).unwrap();
+
+        let action = migrate_legacy_rules_at(temp.path(), InitContext::default()).unwrap();
+        assert_eq!(
+            action,
+            Some(LegacyRulesAction::StrippedSuffix(legacy_file.clone()))
+        );
+        assert!(legacy_file.exists());
+        let updated = fs::read_to_string(&legacy_file).unwrap();
+        assert_eq!(updated, user_content);
+    }
+
+    #[test]
+    fn test_migrate_legacy_rules_foreign_untouched() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        let foreign_content = "Prefer RTK Query for data fetching; do not add axios.";
+        fs::write(&legacy_file, foreign_content).unwrap();
+
+        let action = migrate_legacy_rules_at(temp.path(), InitContext::default()).unwrap();
+        assert_eq!(action, None);
+        assert!(legacy_file.exists());
+        assert_eq!(fs::read_to_string(&legacy_file).unwrap(), foreign_content);
+    }
+
+    #[test]
+    fn test_migrate_legacy_rules_dry_run_leaves_file() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        fs::write(&legacy_file, RTK_AWARENESS_FULL).unwrap();
+
+        let action = migrate_legacy_rules_at(
+            temp.path(),
+            InitContext {
+                dry_run: true,
+                ..InitContext::default()
+            },
+        )
+        .unwrap();
+        assert_eq!(
+            action,
+            Some(LegacyRulesAction::RemovedFile(legacy_file.clone()))
+        );
+        assert!(legacy_file.exists(), "Dry run must not delete file");
+    }
+
+    #[test]
+    fn test_antigravity_uninstall_with_only_legacy_rules_removes_them() {
+        let temp = TempDir::new().unwrap();
+        let legacy_file = temp.path().join(LEGACY_RULES_REL_PATH);
+        fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+        fs::write(&legacy_file, RTK_AWARENESS_FULL).unwrap();
+
+        let removed =
+            uninstall_antigravity_mode_at(temp.path(), false, InitContext::default()).unwrap();
+        assert_eq!(removed.len(), 1);
+        assert!(removed[0].contains("legacy rules file"));
+        assert!(!legacy_file.exists());
+    }
 }
diff --git a/tests/antigravity_hook_test.rs b/tests/antigravity_hook_test.rs
index 98713e60fd..e50ea29ee0 100644
--- a/tests/antigravity_hook_test.rs
+++ b/tests/antigravity_hook_test.rs
@@ -1,4 +1,5 @@
 use serde_json::{Value, json};
+use std::fs;
 use std::io::Write;
 use std::path::Path;
 use std::process::{Output, Stdio};
@@ -240,3 +241,160 @@ fn antigravity_dry_runs_change_nothing() {
         "uninstall dry run must leave the plugin in place"
     );
 }
+
+const LEGACY_AWARENESS: &str = include_str!("../hooks/rtk-awareness-full.md");
+const LEGACY_RULES_PATH: &str = ".agents/rules/antigravity-rtk-rules.md";
+
+#[test]
+fn antigravity_init_removes_exact_match_legacy_rules() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    fs::write(&legacy_file, LEGACY_AWARENESS).unwrap();
+
+    let output = run_init(project.path(), home.path(), &["--agent", "antigravity"]);
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(stdout.contains("Legacy: removed"), "{stdout}");
+    assert!(!legacy_file.exists(), "Legacy file must be removed");
+    assert!(
+        project
+            .path()
+            .join(".agents/plugins/rtk/plugin.json")
+            .is_file(),
+        "Plugin must be installed"
+    );
+}
+
+#[test]
+fn antigravity_init_strips_suffix_preserving_user_content() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    let user_content = "# Project Standards\n\nAlways write tests.";
+    fs::write(
+        &legacy_file,
+        format!("{user_content}\n\n{LEGACY_AWARENESS}"),
+    )
+    .unwrap();
+
+    let output = run_init(project.path(), home.path(), &["--agent", "antigravity"]);
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        stdout.contains("Legacy: removed awareness text from"),
+        "{stdout}"
+    );
+    assert!(legacy_file.exists(), "File with user content must remain");
+    let remaining = fs::read_to_string(&legacy_file).unwrap();
+    assert_eq!(remaining, user_content);
+}
+
+#[test]
+fn antigravity_init_leaves_foreign_rules_untouched() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    let foreign = "Prefer RTK Query for data fetching; do not add axios.";
+    fs::write(&legacy_file, foreign).unwrap();
+
+    let output = run_init(project.path(), home.path(), &["--agent", "antigravity"]);
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(!stdout.contains("Legacy:"), "{stdout}");
+    assert_eq!(fs::read_to_string(&legacy_file).unwrap(), foreign);
+}
+
+#[test]
+fn antigravity_uninstall_removes_legacy_rules() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    fs::write(&legacy_file, LEGACY_AWARENESS).unwrap();
+
+    let output = run_init(
+        project.path(),
+        home.path(),
+        &["--agent", "antigravity", "--uninstall"],
+    );
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        stdout.contains("RTK uninstalled for Google Antigravity:"),
+        "{stdout}"
+    );
+    assert!(stdout.contains("legacy rules file:"), "{stdout}");
+    assert!(!legacy_file.exists());
+}
+
+#[test]
+fn antigravity_dry_run_leaves_legacy_rules_in_place() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    fs::write(&legacy_file, LEGACY_AWARENESS).unwrap();
+
+    let output = run_init(
+        project.path(),
+        home.path(),
+        &["--agent", "antigravity", "--dry-run"],
+    );
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        stdout.contains("[dry-run] would remove legacy rules file:"),
+        "{stdout}"
+    );
+    assert!(stdout.contains("[dry-run] Nothing written."), "{stdout}");
+    assert!(legacy_file.exists(), "Dry-run must not remove legacy file");
+
+    let output = run_init(
+        project.path(),
+        home.path(),
+        &["--agent", "antigravity", "--uninstall", "--dry-run"],
+    );
+    assert!(output.status.success());
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        stdout.contains("[dry-run] would uninstall RTK for Google Antigravity:"),
+        "{stdout}"
+    );
+    assert!(stdout.contains("legacy rules file:"), "{stdout}");
+    assert!(stdout.contains("[dry-run] Nothing written."), "{stdout}");
+    assert!(
+        legacy_file.exists(),
+        "Uninstall dry-run must not remove legacy file"
+    );
+}
+
+#[test]
+fn antigravity_global_init_cleans_workspace_legacy_rules() {
+    let home = tempfile::tempdir().unwrap();
+    let project = tempfile::tempdir().unwrap();
+    let legacy_file = project.path().join(LEGACY_RULES_PATH);
+    fs::create_dir_all(legacy_file.parent().unwrap()).unwrap();
+    fs::write(&legacy_file, LEGACY_AWARENESS).unwrap();
+
+    let output = run_init(
+        project.path(),
+        home.path(),
+        &["-g", "--agent", "antigravity"],
+    );
+    assert!(output.status.success());
+    assert!(
+        !legacy_file.exists(),
+        "Global init in workspace must remove legacy rules"
+    );
+    #[cfg(unix)]
+    assert!(
+        home.path()
+            .join(".gemini/config/plugins/rtk/plugin.json")
+            .is_file(),
+        "Global plugin must be installed"
+    );
+}