diff --git a/README.md b/README.md
index 8a6cab06..cda60658 100644
--- a/README.md
+++ b/README.md
@@ -98,6 +98,15 @@ amplifier notify reset --all [--scope]               # Clear all notification se
 
 ```
 
+**Note on `extra_request_params`:** some provider modules support an
+`extra_request_params` key inside a provider's `config` block -- a raw,
+user-owned dict of request parameters merged verbatim into every API call
+for options the module doesn't wrap itself. It is entirely your
+responsibility to maintain by hand in `settings.yaml`; config tooling
+(`provider add`/`provider edit`/`provider manage`) round-trips it untouched
+across reconfigures but never prompts for it, displays it in the wizard, or
+validates its contents.
+
 ### Session Commands
 
 ```bash
diff --git a/amplifier_app_cli/commands/provider.py b/amplifier_app_cli/commands/provider.py
index 6d27725b..8b9fb2e1 100644
--- a/amplifier_app_cli/commands/provider.py
+++ b/amplifier_app_cli/commands/provider.py
@@ -18,6 +18,7 @@
 from ..provider_config_utils import (
     _config_claimed_env_vars,
     _normalize_id,
+    _preserve_reserved_keys,
     _secret_env_var_for,
     _secret_field_id_for,
     _suggest_instance_env_var,
@@ -650,6 +651,18 @@ def provider_add(ctx: click.Context, provider_type: str | None, scope: str) -> N
         if instance_id:
             scope_providers.append(provider_entry)
         else:
+            # An entry with this module may already be present here (e.g. a
+            # concurrent write landed between our pre-lock read and this
+            # one). Round-trip its reserved, user-owned keys (e.g.
+            # extra_request_params) before it's dropped -- see
+            # _preserve_reserved_keys()'s docstring.
+            old_entry = next(
+                (p for p in scope_providers if p.get("module") == module_id), None
+            )
+            if old_entry is not None:
+                provider_entry["config"] = _preserve_reserved_keys(
+                    old_entry.get("config"), provider_entry["config"]
+                )
             # Replace any existing entry with same module
             scope_providers = [
                 p for p in scope_providers if p.get("module") != module_id
@@ -939,6 +952,12 @@ def provider_edit(name: str, scope: str) -> None:
         console.print("[red]Configuration cancelled.[/red]")
         return
 
+    # Round-trip reserved, user-owned keys (e.g. extra_request_params) that
+    # the wizard never collects -- see _preserve_reserved_keys()'s docstring.
+    new_config = _preserve_reserved_keys(
+        existing_config if isinstance(existing_config, dict) else None, new_config
+    )
+
     # Preserve priority from existing config
     priority = (
         existing_config.get("priority", 1) if isinstance(existing_config, dict) else 1
@@ -1427,6 +1446,18 @@ def _manage_add_provider(settings: AppSettings, scope: Scope = "global") -> None
         if instance_id:
             scope_providers.append(provider_entry)
         else:
+            # An entry with this module may already be present here (e.g. a
+            # concurrent write landed between our pre-lock read and this
+            # one). Round-trip its reserved, user-owned keys (e.g.
+            # extra_request_params) before it's dropped -- see
+            # _preserve_reserved_keys()'s docstring.
+            old_entry = next(
+                (p for p in scope_providers if p.get("module") == module_id), None
+            )
+            if old_entry is not None:
+                provider_entry["config"] = _preserve_reserved_keys(
+                    old_entry.get("config"), provider_entry["config"]
+                )
             scope_providers = [
                 p for p in scope_providers if p.get("module") != module_id
             ]
@@ -1496,6 +1527,12 @@ def _manage_edit_provider(
         console.print("  [red]Configuration cancelled.[/red]")
         return
 
+    # Round-trip reserved, user-owned keys (e.g. extra_request_params) that
+    # the wizard never collects -- see _preserve_reserved_keys()'s docstring.
+    new_config = _preserve_reserved_keys(
+        existing_config if isinstance(existing_config, dict) else None, new_config
+    )
+
     priority = (
         existing_config.get("priority", 1) if isinstance(existing_config, dict) else 1
     )
diff --git a/amplifier_app_cli/provider_config_utils.py b/amplifier_app_cli/provider_config_utils.py
index 74cf73a6..96b60ae2 100644
--- a/amplifier_app_cli/provider_config_utils.py
+++ b/amplifier_app_cli/provider_config_utils.py
@@ -26,6 +26,50 @@
 console = Console()
 logger = logging.getLogger(__name__)
 
+# Reserved, user-owned provider-config keys. Provider modules are adopting
+# ``extra_request_params`` as an owner-beware dict merged verbatim into every
+# API request, for parameters the module itself doesn't wrap -- users
+# maintain it by hand in settings.yaml. It is deliberately never declared as
+# a ConfigField (never a wizard prompt, never displayed, never validated),
+# so every config-rewrite path that rebuilds a provider's config purely from
+# wizard-collected fields must round-trip it verbatim via
+# ``_preserve_reserved_keys()`` below rather than silently dropping it. Keep
+# this tuple as the single, deliberately narrow allow-list for that
+# passthrough convention -- do not widen it to cover arbitrary unknown keys.
+RESERVED_PROVIDER_CONFIG_KEYS: tuple[str, ...] = ("extra_request_params",)
+
+
+def _preserve_reserved_keys(
+    old_config: dict[str, Any] | None, new_config: dict[str, Any]
+) -> dict[str, Any]:
+    """Carry forward reserved, user-owned config keys from ``old_config``
+    into ``new_config`` verbatim, if present.
+
+    Called wherever a config-rewrite path replaces an EXISTING provider
+    instance's config with a freshly wizard-collected one. Only keys in
+    ``RESERVED_PROVIDER_CONFIG_KEYS`` (today, just ``extra_request_params``)
+    are preserved -- any other non-schema key in ``old_config`` is dropped,
+    exactly as before this function existed. If ``new_config`` already
+    carries the key (e.g. a module surfaces it deliberately in the future),
+    the old value is not used -- the freshly collected value wins.
+
+    Args:
+        old_config: The provider instance's config before this reconfigure,
+            or None if this is a fresh instance with no prior config.
+        new_config: The config just rebuilt from wizard/schema answers.
+
+    Returns:
+        ``new_config``, with any missing reserved keys copied in from
+        ``old_config``. Never mutates either input in place.
+    """
+    if not old_config:
+        return new_config
+    result = new_config
+    for key in RESERVED_PROVIDER_CONFIG_KEYS:
+        if key in old_config and key not in result:
+            result = {**result, key: old_config[key]}
+    return result
+
 
 def _prompt_model_selection(
     provider_id: str,
diff --git a/tests/test_provider_config_reserved_keys.py b/tests/test_provider_config_reserved_keys.py
new file mode 100644
index 00000000..d264be7e
--- /dev/null
+++ b/tests/test_provider_config_reserved_keys.py
@@ -0,0 +1,372 @@
+"""Tests for round-tripping reserved, user-owned provider-config keys.
+
+Provider modules are adopting an ``extra_request_params`` config key -- an
+owner-beware dict merged verbatim into every API request, for parameters the
+module itself doesn't wrap. Users maintain this key by hand in
+settings.yaml; it is never declared as a ``ConfigField`` by any provider
+module and the wizard never prompts for it.
+
+Bug: every edit/reconfigure flow rebuilds a provider's config purely from the
+module's declared ``ConfigField`` schema answers (``configure_provider()``
+in ``provider_config_utils.py``), then callers assign the rebuilt dict
+wholesale over the old one. Any key not in the schema -- including
+``extra_request_params`` -- is silently DROPPED on edit, defeating the whole
+point of a hand-maintained passthrough bag.
+
+Fix: ``_preserve_reserved_keys(old, new)`` in provider_config_utils.py
+carries ``extra_request_params`` forward verbatim from the prior config into
+the rebuilt one, if present, at every seam that replaces an EXISTING
+provider instance's config:
+
+    * ``provider_edit()``          (commands/provider.py)
+    * ``_manage_edit_provider()``  (commands/provider.py, interactive loop)
+    * ``provider_add()``           (commands/provider.py, same-module
+                                     replace-without-id branch)
+    * ``_manage_add_provider()``   (commands/provider.py, interactive loop,
+                                     same branch)
+
+Covers:
+    (a) edit flow preserves extra_request_params verbatim
+    (b) edit flow still drops an arbitrary non-schema key (deliberately narrow)
+    (c) the wizard never prompts for extra_request_params, even with an
+        empty config_fields schema
+    (d) a fresh add (no prior config) never invents the key
+    (e) unit coverage of _preserve_reserved_keys() itself
+"""
+
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+from click.testing import CliRunner
+
+import amplifier_app_cli.provider_config_utils as pcu
+from amplifier_app_cli.lib.settings import AppSettings, SettingsPaths
+
+
+def _make_settings(tmp_path: Path) -> AppSettings:
+    """Create AppSettings with isolated paths for testing."""
+    paths = SettingsPaths(
+        global_settings=tmp_path / "global" / "settings.yaml",
+        project_settings=tmp_path / "project" / "settings.yaml",
+        local_settings=tmp_path / "local" / "settings.local.yaml",
+    )
+    return AppSettings(paths=paths)
+
+
+def _seed_provider(
+    settings: AppSettings,
+    module: str,
+    config: dict,
+    priority: int = 1,
+    provider_id: str | None = None,
+) -> None:
+    """Seed a provider entry into global settings for testing.
+
+    Bypasses the plaintext-secret normalization that ``_write_scope`` now
+    performs on every provider write, by making the provider module
+    unresolvable for the duration of the seed write -- these tests seed
+    literal config values purely for test setup. Mirrors the helper in
+    test_provider_commands.py.
+    """
+    entry = {
+        "module": module,
+        "config": {**config, "priority": priority},
+    }
+    if provider_id is not None:
+        entry["id"] = provider_id
+    with patch(
+        "amplifier_app_cli.provider_config_utils.get_provider_info",
+        return_value=None,
+    ):
+        settings.set_provider_override(entry, scope="global")
+
+
+# ============================================================
+# (a)/(b): provider edit round-trips extra_request_params, drops other
+# non-schema keys
+# ============================================================
+
+
+class TestProviderEditPreservesExtraRequestParams:
+    """`amplifier provider edit` must round-trip extra_request_params
+    verbatim while continuing to drop unrelated non-schema keys."""
+
+    def test_edit_preserves_extra_request_params_verbatim(self, tmp_path):
+        """(a) An existing config carrying extra_request_params survives a
+        full reconfigure -- verbatim, not just present."""
+        settings = _make_settings(tmp_path)
+        _seed_provider(
+            settings,
+            "provider-anthropic",
+            {
+                "default_model": "claude-sonnet-4-6",
+                "extra_request_params": {"service_tier": "fast"},
+            },
+            priority=1,
+        )
+
+        from amplifier_app_cli.commands.provider import provider
+
+        runner = CliRunner()
+        with (
+            patch(
+                "amplifier_app_cli.commands.provider._get_settings",
+                return_value=settings,
+            ),
+            patch("amplifier_app_cli.commands.provider._ensure_providers_ready"),
+            patch(
+                "amplifier_app_cli.commands.provider.configure_provider",
+                # Simulates a full wizard rebuild that only knows about
+                # schema-declared fields -- no knowledge of
+                # extra_request_params at all.
+                return_value={"default_model": "claude-opus-4-6"},
+            ),
+            patch("amplifier_app_cli.commands.provider.KeyManager"),
+        ):
+            result = runner.invoke(provider, ["edit", "anthropic"])
+
+        assert result.exit_code == 0, f"Output: {result.output}"
+        providers = settings.get_scope_provider_overrides("global")
+        assert len(providers) == 1
+        config = providers[0]["config"]
+        assert config.get("extra_request_params") == {"service_tier": "fast"}, (
+            f"extra_request_params was dropped or altered on edit: {config}"
+        )
+        assert config["default_model"] == "claude-opus-4-6"
+
+    def test_edit_still_drops_unrelated_non_schema_key(self, tmp_path):
+        """(b) The preservation is deliberately narrow: some_stale_key (not
+        a reserved key, not a schema field) must still be dropped on edit,
+        exactly as before this fix."""
+        settings = _make_settings(tmp_path)
+        _seed_provider(
+            settings,
+            "provider-anthropic",
+            {
+                "default_model": "claude-sonnet-4-6",
+                "some_stale_key": "leftover-value",
+            },
+            priority=1,
+        )
+
+        from amplifier_app_cli.commands.provider import provider
+
+        runner = CliRunner()
+        with (
+            patch(
+                "amplifier_app_cli.commands.provider._get_settings",
+                return_value=settings,
+            ),
+            patch("amplifier_app_cli.commands.provider._ensure_providers_ready"),
+            patch(
+                "amplifier_app_cli.commands.provider.configure_provider",
+                return_value={"default_model": "claude-opus-4-6"},
+            ),
+            patch("amplifier_app_cli.commands.provider.KeyManager"),
+        ):
+            result = runner.invoke(provider, ["edit", "anthropic"])
+
+        assert result.exit_code == 0, f"Output: {result.output}"
+        providers = settings.get_scope_provider_overrides("global")
+        config = providers[0]["config"]
+        assert "some_stale_key" not in config, (
+            "some_stale_key is not a reserved key and must still be dropped "
+            f"on edit (preservation must stay narrow): {config}"
+        )
+
+    def test_manage_edit_preserves_extra_request_params_verbatim(self, tmp_path):
+        """(a), interactive-manage-loop variant: `_manage_edit_provider()`
+        must apply the same preservation as `provider_edit()`."""
+        from amplifier_app_cli.commands.provider import _manage_edit_provider
+
+        settings = _make_settings(tmp_path)
+        _seed_provider(
+            settings,
+            "provider-anthropic",
+            {
+                "default_model": "claude-sonnet-4-6",
+                "extra_request_params": {"service_tier": "fast"},
+            },
+            priority=1,
+        )
+        providers = settings.get_provider_overrides()
+
+        with (
+            patch(
+                "amplifier_app_cli.commands.provider.configure_provider",
+                return_value={"default_model": "claude-opus-4-6"},
+            ),
+            patch("amplifier_app_cli.commands.provider.KeyManager"),
+        ):
+            _manage_edit_provider(settings, "e1", providers, scope="global")
+
+        updated = settings.get_scope_provider_overrides("global")
+        config = updated[0]["config"]
+        assert config.get("extra_request_params") == {"service_tier": "fast"}, (
+            f"extra_request_params was dropped by _manage_edit_provider: {config}"
+        )
+
+
+# ============================================================
+# (c): the wizard never prompts for extra_request_params
+# ============================================================
+
+
+class TestWizardNeverPromptsForExtraRequestParams:
+    """extra_request_params must never become a ConfigField -- it is never
+    displayed, never prompted for, never validated -- even in a
+    pathological case where a module declares no config_fields at all."""
+
+    def test_configure_provider_never_prompts_with_empty_schema(self, monkeypatch):
+        monkeypatch.setenv("TESTPROV_API_KEY", "sk-existing")
+        with (
+            patch(
+                "amplifier_app_cli.provider_config_utils.get_provider_info",
+                return_value={"display_name": "Test Provider", "config_fields": []},
+            ),
+            patch(
+                "amplifier_app_cli.provider_config_utils.get_provider_models",
+                return_value=[],
+            ),
+            patch("amplifier_app_cli.provider_config_utils.console", MagicMock()),
+            patch("amplifier_app_cli.provider_config_utils.Prompt.ask") as mock_ask,
+        ):
+            mock_ask.side_effect = lambda *a, **kw: kw.get("default", "")
+            result = pcu.configure_provider(
+                "test-provider",
+                MagicMock(),
+                existing_config={
+                    "default_model": "m",
+                    "extra_request_params": {"service_tier": "fast"},
+                },
+            )
+
+        assert result is not None
+        assert "extra_request_params" not in result, (
+            "configure_provider() must never surface extra_request_params "
+            f"as a collected/prompted field: {result}"
+        )
+        # Every prompt call's field label must never mention it either.
+        for call in mock_ask.call_args_list:
+            rendered = " ".join(str(a) for a in call.args) + " ".join(
+                str(v) for v in call.kwargs.values()
+            )
+            assert "extra_request_params" not in rendered
+
+
+# ============================================================
+# (d): fresh add never invents the key
+# ============================================================
+
+
+class TestFreshAddNeverInventsExtraRequestParams:
+    """A brand-new provider instance (no prior config) must never gain an
+    extra_request_params key out of nowhere."""
+
+    def test_provider_add_fresh_no_prior_config(self, tmp_path, monkeypatch):
+        monkeypatch.setattr(Path, "home", lambda: tmp_path)
+        from amplifier_app_cli.commands.provider import provider
+
+        settings = _make_settings(tmp_path)
+
+        runner = CliRunner()
+        with (
+            patch(
+                "amplifier_app_cli.commands.provider._get_settings",
+                return_value=settings,
+            ),
+            patch("amplifier_app_cli.commands.provider._ensure_providers_ready"),
+            patch("amplifier_app_cli.commands.provider.ProviderManager") as mock_pm_cls,
+            patch(
+                "amplifier_app_cli.commands.provider.configure_provider",
+                return_value={"default_model": "claude-opus-4-6"},
+            ),
+            patch("amplifier_app_cli.commands.provider.KeyManager"),
+        ):
+            mock_pm_cls.return_value.list_providers.return_value = [
+                ("provider-anthropic", "Anthropic", "desc")
+            ]
+            result = runner.invoke(provider, ["add", "anthropic"])
+
+        assert result.exit_code == 0, f"Output: {result.output}"
+        providers = settings.get_scope_provider_overrides("global")
+        assert len(providers) == 1
+        config = providers[0]["config"]
+        assert "extra_request_params" not in config, (
+            f"Fresh add must never invent extra_request_params: {config}"
+        )
+
+    def test_manage_add_provider_fresh_no_prior_config(self, tmp_path, monkeypatch):
+        monkeypatch.setattr(Path, "home", lambda: tmp_path)
+        from amplifier_app_cli.commands.provider import _manage_add_provider
+
+        settings = _make_settings(tmp_path)
+
+        with (
+            patch("amplifier_app_cli.commands.provider.ProviderManager") as mock_pm_cls,
+            patch(
+                "amplifier_app_cli.commands.provider.configure_provider",
+                return_value={"default_model": "claude-opus-4-6"},
+            ),
+            patch("amplifier_app_cli.commands.provider.KeyManager"),
+            patch(
+                "amplifier_app_cli.commands.provider.Prompt.ask",
+                return_value="1",
+            ),
+        ):
+            mock_pm_cls.return_value.list_providers.return_value = [
+                ("provider-anthropic", "Anthropic", "desc")
+            ]
+            _manage_add_provider(settings, scope="global")
+
+        providers = settings.get_scope_provider_overrides("global")
+        assert len(providers) == 1
+        config = providers[0]["config"]
+        assert "extra_request_params" not in config, (
+            f"Fresh add (manage loop) must never invent extra_request_params: {config}"
+        )
+
+
+# ============================================================
+# (e): unit coverage of the helper itself
+# ============================================================
+
+
+class TestPreserveReservedKeysHelper:
+    """Direct unit coverage of _preserve_reserved_keys()."""
+
+    def test_preserves_extra_request_params_when_present_in_old(self):
+        old = {"default_model": "x", "extra_request_params": {"a": 1}}
+        new = {"default_model": "y"}
+        result = pcu._preserve_reserved_keys(old, new)
+        assert result["extra_request_params"] == {"a": 1}
+        assert result["default_model"] == "y"
+
+    def test_does_not_override_if_new_already_has_it(self):
+        """If new already carries the key (e.g. a future module surfaces it
+        deliberately), the old value must not clobber it."""
+        old = {"extra_request_params": {"a": 1}}
+        new = {"extra_request_params": {"b": 2}}
+        result = pcu._preserve_reserved_keys(old, new)
+        assert result["extra_request_params"] == {"b": 2}
+
+    def test_no_old_config_is_a_noop(self):
+        new = {"default_model": "y"}
+        result = pcu._preserve_reserved_keys(None, new)
+        assert result == {"default_model": "y"}
+        assert "extra_request_params" not in result
+
+    def test_old_without_reserved_key_adds_nothing(self):
+        old = {"default_model": "x"}
+        new = {"default_model": "y"}
+        result = pcu._preserve_reserved_keys(old, new)
+        assert result == {"default_model": "y"}
+
+    def test_only_the_declared_reserved_keys_are_preserved(self):
+        """Narrow by construction: an arbitrary non-schema key in old is
+        never carried forward, only entries in RESERVED_PROVIDER_CONFIG_KEYS."""
+        old = {"extra_request_params": {"a": 1}, "some_stale_key": "leftover"}
+        new = {}
+        result = pcu._preserve_reserved_keys(old, new)
+        assert result == {"extra_request_params": {"a": 1}}
+        assert "some_stale_key" not in result