diff --git a/extensions/git/extension.yml b/extensions/git/extension.yml
index 13c1977ea..6edb65ddc 100644
--- a/extensions/git/extension.yml
+++ b/extensions/git/extension.yml
@@ -8,6 +8,13 @@ extension:
   author: spec-kit-core
   repository: https://github.com/github/spec-kit
   license: MIT
+  install_notice: |
+    The git extension is currently enabled by default, but starting with
+    specify-cli v1.0.0 it will require explicit opt-in.
+
+    To opt in after specify-cli v1.0.0:
+      • specify init --extension git
+      • specify extension add git  (post-init)
 
 requires:
   speckit_version: ">=0.2.0"
diff --git a/src/specify_cli/__init__.py b/src/specify_cli/__init__.py
index 8c6fd02b9..f771a8078 100644
--- a/src/specify_cli/__init__.py
+++ b/src/specify_cli/__init__.py
@@ -1277,6 +1277,8 @@ def init(
 
             ensure_constitution_from_template(project_path, tracker=tracker)
 
+            _git_ext_freshly_installed = False
+            _git_ext_install_notice: str | None = None
             if not no_git:
                 tracker.start("git")
                 git_messages = []
@@ -1307,10 +1309,12 @@ def init(
                         if manager.registry.is_installed("git"):
                             git_messages.append("extension already installed")
                         else:
-                            manager.install_from_directory(
+                            ext_manifest = manager.install_from_directory(
                                 bundled_path, get_speckit_version()
                             )
                             git_messages.append("extension installed")
+                            _git_ext_freshly_installed = True
+                            _git_ext_install_notice = ext_manifest.install_notice
                     else:
                         git_has_error = True
                         git_messages.append("bundled extension not found")
@@ -1454,6 +1458,19 @@ def init(
     console.print(tracker.render())
     console.print("\n[bold green]Project ready.[/bold green]")
 
+    if _git_ext_freshly_installed and isinstance(_git_ext_install_notice, str):
+        _git_ext_notice_text = _git_ext_install_notice.strip()
+        if _git_ext_notice_text:
+            console.print()
+            console.print(
+                Panel(
+                    _git_ext_notice_text,
+                    title="[yellow]⚠ Deprecation notice: git extension[/yellow]",
+                    border_style="yellow",
+                    padding=(1, 2),
+                )
+            )
+
     # Agent folder security notice
     agent_config = AGENT_CONFIG.get(selected_ai)
     if agent_config:
diff --git a/src/specify_cli/extensions.py b/src/specify_cli/extensions.py
index d5543cd0b..dfc631a53 100644
--- a/src/specify_cli/extensions.py
+++ b/src/specify_cli/extensions.py
@@ -346,6 +346,20 @@ def hooks(self) -> Dict[str, Any]:
         """Get hook definitions."""
         return self.data.get("hooks", {})
 
+    @property
+    def install_notice(self) -> str | None:
+        """Get optional install notice message.
+
+        Extensions can specify an 'install_notice' field to display
+        important information to users when the extension is first installed.
+        """
+        notice = self.data.get("extension", {}).get("install_notice")
+        if notice is None:
+            return None
+        if isinstance(notice, str):
+            return notice
+        return str(notice)
+
     def get_hash(self) -> str:
         """Calculate SHA256 hash of manifest file."""
         with open(self.path, 'rb') as f:
diff --git a/tests/extensions/git/test_git_extension.py b/tests/extensions/git/test_git_extension.py
index c4f986d17..ec15f54f6 100644
--- a/tests/extensions/git/test_git_extension.py
+++ b/tests/extensions/git/test_git_extension.py
@@ -837,3 +837,130 @@ def test_test_feature_branch_accepts_single_prefix(self, tmp_path: Path):
             text=True,
         )
         assert result.returncode == 0
+
+
+# ── Deprecation Notice Tests ──────────────────────────────────────────────────
+
+
+class TestGitExtDeprecationNotice:
+    """Tests for the v1.0.0 deprecation notice shown during specify init."""
+
+    def test_deprecation_notice_shown_on_fresh_install(self, tmp_path: Path):
+        """specify init shows the git extension deprecation notice on first install."""
+        from typer.testing import CliRunner
+        from unittest.mock import patch, MagicMock
+        from specify_cli import app
+        from tests.conftest import strip_ansi
+
+        project_dir = tmp_path / "test-project"
+        runner = CliRunner()
+
+        mock_manifest = MagicMock()
+        mock_manifest.install_notice = (
+            "The git extension is currently enabled by default, but starting with\n"
+            "specify-cli v1.0.0 it will require explicit opt-in.\n\n"
+            "To opt in after specify-cli v1.0.0:\n"
+            "  • specify init --extension git\n"
+            "  • specify extension add git  (post-init)"
+        )
+
+        mock_registry = MagicMock()
+        mock_registry.is_installed.return_value = False
+
+        mock_manager = MagicMock()
+        mock_manager.registry = mock_registry
+        mock_manager.install_from_directory.return_value = mock_manifest
+
+        # Patch _locate_bundled_extension to ensure deterministic behavior
+        with patch("specify_cli.extensions.ExtensionManager", return_value=mock_manager), \
+             patch("specify_cli._locate_bundled_extension", return_value=tmp_path):
+            result = runner.invoke(
+                app,
+                ["init", str(project_dir), "--ai", "claude", "--ignore-agent-tools", "--script", "sh"],
+                catch_exceptions=False,
+            )
+
+        assert result.exit_code == 0, result.output
+        plain = strip_ansi(result.output)
+        assert "Deprecation notice: git extension" in plain
+        assert "v1.0.0" in plain
+        assert "specify extension add git" in plain
+
+    def test_deprecation_notice_not_shown_when_already_installed(self, tmp_path: Path):
+        """specify init does NOT show the deprecation notice when git extension is already installed."""
+        from typer.testing import CliRunner
+        from unittest.mock import patch, MagicMock
+        from specify_cli import app
+        from tests.conftest import strip_ansi
+
+        project_dir = tmp_path / "test-project"
+        runner = CliRunner()
+
+        mock_registry = MagicMock()
+        mock_registry.is_installed.return_value = True
+
+        mock_manager = MagicMock()
+        mock_manager.registry = mock_registry
+
+        with patch("specify_cli.extensions.ExtensionManager", return_value=mock_manager), \
+             patch("specify_cli._locate_bundled_extension", return_value=tmp_path):
+            result = runner.invoke(
+                app,
+                ["init", str(project_dir), "--ai", "claude", "--ignore-agent-tools", "--script", "sh"],
+                catch_exceptions=False,
+            )
+
+        assert result.exit_code == 0, result.output
+        plain = strip_ansi(result.output)
+        assert "Deprecation notice: git extension" not in plain
+
+    def test_deprecation_notice_not_shown_with_no_git_flag(self, tmp_path: Path):
+        """specify init does NOT show the deprecation notice when --no-git is passed."""
+        from typer.testing import CliRunner
+        from specify_cli import app
+        from tests.conftest import strip_ansi
+
+        project_dir = tmp_path / "test-project"
+        runner = CliRunner()
+
+        result = runner.invoke(
+            app,
+            ["init", str(project_dir), "--ai", "claude", "--ignore-agent-tools", "--no-git", "--script", "sh"],
+            catch_exceptions=False,
+        )
+
+        assert result.exit_code == 0, result.output
+        plain = strip_ansi(result.output)
+        assert "Deprecation notice: git extension" not in plain
+
+    def test_deprecation_notice_not_shown_when_no_install_notice(self, tmp_path: Path):
+        """specify init does NOT show the deprecation notice if extension has no install_notice."""
+        from typer.testing import CliRunner
+        from unittest.mock import patch, MagicMock
+        from specify_cli import app
+        from tests.conftest import strip_ansi
+
+        project_dir = tmp_path / "test-project"
+        runner = CliRunner()
+
+        mock_manifest = MagicMock()
+        mock_manifest.install_notice = None  # No notice defined
+
+        mock_registry = MagicMock()
+        mock_registry.is_installed.return_value = False
+
+        mock_manager = MagicMock()
+        mock_manager.registry = mock_registry
+        mock_manager.install_from_directory.return_value = mock_manifest
+
+        with patch("specify_cli.extensions.ExtensionManager", return_value=mock_manager), \
+             patch("specify_cli._locate_bundled_extension", return_value=tmp_path):
+            result = runner.invoke(
+                app,
+                ["init", str(project_dir), "--ai", "claude", "--ignore-agent-tools", "--script", "sh"],
+                catch_exceptions=False,
+            )
+
+        assert result.exit_code == 0, result.output
+        plain = strip_ansi(result.output)
+        assert "Deprecation notice: git extension" not in plain