diff --git a/Cargo.lock b/Cargo.lock
index 9742d37ef..dd33b7672 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4961,7 +4961,6 @@ dependencies = [
 name = "uv-requirements"
 version = "0.1.0"
 dependencies = [
- "anstream",
  "anyhow",
  "cache-key",
  "configparser",
diff --git a/crates/uv-cli/src/lib.rs b/crates/uv-cli/src/lib.rs
index 72cba19a9..f94d3af33 100644
--- a/crates/uv-cli/src/lib.rs
+++ b/crates/uv-cli/src/lib.rs
@@ -1784,6 +1784,14 @@ pub struct RunArgs {
 #[derive(Args)]
 #[allow(clippy::struct_excessive_bools)]
 pub struct SyncArgs {
+    /// Assert that the `uv.lock` will remain unchanged.
+    #[arg(long, conflicts_with = "frozen")]
+    pub locked: bool,
+
+    /// Install without updating the `uv.lock` file.
+    #[arg(long, conflicts_with = "locked")]
+    pub frozen: bool,
+
     /// Include optional dependencies from the extra group name; may be provided more than once.
     /// Only applies to `pyproject.toml`, `setup.py`, and `setup.cfg` sources.
     #[arg(long, conflicts_with = "all_extras", value_parser = extra_name_with_clap_error)]
@@ -1811,7 +1819,7 @@ pub struct SyncArgs {
     pub no_clean: bool,
 
     #[command(flatten)]
-    pub installer: InstallerArgs,
+    pub installer: ResolverInstallerArgs,
 
     #[command(flatten)]
     pub build: BuildArgs,
diff --git a/crates/uv-requirements/Cargo.toml b/crates/uv-requirements/Cargo.toml
index 77fe9202e..28e6da027 100644
--- a/crates/uv-requirements/Cargo.toml
+++ b/crates/uv-requirements/Cargo.toml
@@ -29,7 +29,6 @@ uv-resolver = { workspace = true, features = ["clap"] }
 uv-types = { workspace = true }
 uv-warnings = { workspace = true }
 
-anstream = { workspace = true }
 anyhow = { workspace = true }
 configparser = { workspace = true }
 console = { workspace = true }
diff --git a/crates/uv-requirements/src/upgrade.rs b/crates/uv-requirements/src/upgrade.rs
index 669f566c5..5e22b854b 100644
--- a/crates/uv-requirements/src/upgrade.rs
+++ b/crates/uv-requirements/src/upgrade.rs
@@ -1,12 +1,10 @@
 use std::path::Path;
 
-use anstream::eprint;
 use anyhow::Result;
 
 use requirements_txt::RequirementsTxt;
 use uv_client::{BaseClientBuilder, Connectivity};
 use uv_configuration::Upgrade;
-use uv_distribution::Workspace;
 use uv_git::ResolvedRepositoryReference;
 use uv_resolver::{Lock, Preference, PreferenceError};
 
@@ -63,34 +61,6 @@ pub async fn read_requirements_txt(
     })
 }
 
-/// Load the lockfile from the workspace.
-///
-/// Returns `Ok(None)` if the lockfile does not exist, is invalid, or is not required for the given upgrade strategy.
-pub async fn read_lockfile(workspace: &Workspace, upgrade: &Upgrade) -> Result<Option<Lock>> {
-    // As an optimization, skip reading the lockfile is we're upgrading all packages anyway.
-    if upgrade.is_all() {
-        return Ok(None);
-    }
-
-    // If an existing lockfile exists, build up a set of preferences.
-    let lockfile = workspace.install_path().join("uv.lock");
-    let lock = match fs_err::tokio::read_to_string(&lockfile).await {
-        Ok(encoded) => match toml::from_str::<Lock>(&encoded) {
-            Ok(lock) => lock,
-            Err(err) => {
-                eprint!("Failed to parse lockfile; ignoring locked requirements: {err}");
-                return Ok(None);
-            }
-        },
-        Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
-            return Ok(None);
-        }
-        Err(err) => return Err(err.into()),
-    };
-
-    Ok(Some(lock))
-}
-
 /// Load the preferred requirements from an existing lockfile, applying the upgrade strategy.
 pub fn read_lock_requirements(lock: &Lock, upgrade: &Upgrade) -> LockedRequirements {
     let mut preferences = Vec::new();
diff --git a/crates/uv/src/commands/project/add.rs b/crates/uv/src/commands/project/add.rs
index ea851c7fa..2c8e1e6ac 100644
--- a/crates/uv/src/commands/project/add.rs
+++ b/crates/uv/src/commands/project/add.rs
@@ -10,6 +10,7 @@ use uv_distribution::pyproject_mut::PyProjectTomlMut;
 use uv_distribution::{DistributionDatabase, ProjectWorkspace, VirtualProject, Workspace};
 use uv_normalize::PackageName;
 use uv_python::{PythonFetch, PythonPreference, PythonRequest};
+
 use uv_requirements::{NamedRequirementsResolver, RequirementsSource, RequirementsSpecification};
 use uv_resolver::FlatIndex;
 use uv_types::{BuildIsolation, HashStrategy};
@@ -17,6 +18,7 @@ use uv_warnings::warn_user_once;
 
 use crate::commands::pip::operations::Modifications;
 use crate::commands::pip::resolution_environment;
+use crate::commands::project::lock::commit;
 use crate::commands::reporters::ResolverReporter;
 use crate::commands::{project, ExitStatus, SharedState};
 use crate::printer::Printer;
@@ -204,10 +206,14 @@ pub(crate) async fn add(
     // Initialize any shared state.
     let state = SharedState::default();
 
-    // Lock and sync the environment.
+    // Read the existing lockfile.
+    let existing = project::lock::read(project.workspace()).await?;
+
+    // Lock and sync the environment, if necessary.
     let lock = project::lock::do_lock(
         project.workspace(),
         venv.interpreter(),
+        existing.as_ref(),
         settings.as_ref().into(),
         &state,
         preview,
@@ -218,6 +224,9 @@ pub(crate) async fn add(
         printer,
     )
     .await?;
+    if !existing.is_some_and(|existing| existing == lock) {
+        commit(&lock, project.workspace()).await?;
+    }
 
     // Perform a full sync, because we don't know what exactly is affected by the removal.
     // TODO(ibraheem): Should we accept CLI overrides for this? Should we even sync here?
diff --git a/crates/uv/src/commands/project/lock.rs b/crates/uv/src/commands/project/lock.rs
index 678ae7282..0a815814d 100644
--- a/crates/uv/src/commands/project/lock.rs
+++ b/crates/uv/src/commands/project/lock.rs
@@ -8,7 +8,7 @@ use uv_dispatch::BuildDispatch;
 use uv_distribution::{Workspace, DEV_DEPENDENCIES};
 use uv_git::ResolvedRepositoryReference;
 use uv_python::{Interpreter, PythonFetch, PythonPreference, PythonRequest};
-use uv_requirements::upgrade::{read_lock_requirements, read_lockfile, LockedRequirements};
+use uv_requirements::upgrade::{read_lock_requirements, LockedRequirements};
 use uv_resolver::{FlatIndex, Lock, OptionsBuilder, PythonRequirement, RequiresPython};
 use uv_types::{BuildIsolation, EmptyInstalledPackages, HashStrategy};
 use uv_warnings::{warn_user, warn_user_once};
@@ -52,10 +52,14 @@ pub(crate) async fn lock(
     .await?
     .into_interpreter();
 
+    // Read the existing lockfile.
+    let existing = read(&workspace).await?;
+
     // Perform the lock operation.
     match do_lock(
         &workspace,
         &interpreter,
+        existing.as_ref(),
         settings.as_ref(),
         &SharedState::default(),
         preview,
@@ -67,7 +71,12 @@ pub(crate) async fn lock(
     )
     .await
     {
-        Ok(_) => Ok(ExitStatus::Success),
+        Ok(lock) => {
+            if !existing.is_some_and(|existing| existing == lock) {
+                commit(&lock, &workspace).await?;
+            }
+            Ok(ExitStatus::Success)
+        }
         Err(ProjectError::Operation(pip::operations::Error::Resolve(
             uv_resolver::ResolveError::NoSolution(err),
         ))) => {
@@ -84,6 +93,7 @@ pub(crate) async fn lock(
 pub(super) async fn do_lock(
     workspace: &Workspace,
     interpreter: &Interpreter,
+    existing: Option<&Lock>,
     settings: ResolverSettingsRef<'_>,
     state: &SharedState,
     preview: PreviewMode,
@@ -175,9 +185,7 @@ pub(super) async fn do_lock(
     };
 
     // If an existing lockfile exists, build up a set of preferences.
-    let existing_lock = read_lockfile(workspace, upgrade).await?;
-    let LockedRequirements { preferences, git } = existing_lock
-        .as_ref()
+    let LockedRequirements { preferences, git } = existing
         .map(|lock| read_lock_requirements(lock, upgrade))
         .unwrap_or_default();
 
@@ -238,15 +246,29 @@ pub(super) async fn do_lock(
     // Notify the user of any resolution diagnostics.
     pip::operations::diagnose_resolution(resolution.diagnostics(), printer)?;
 
-    // Avoid serializing and writing to disk if the lock hasn't changed.
-    let lock = Lock::from_resolution_graph(&resolution)?;
-    if existing_lock.is_some_and(|existing_lock| existing_lock == lock) {
-        return Ok(lock);
-    }
-
-    // Write the lockfile to disk.
-    let encoded = lock.to_toml()?;
-    fs_err::tokio::write(workspace.install_path().join("uv.lock"), encoded.as_bytes()).await?;
-
-    Ok(lock)
+    Ok(Lock::from_resolution_graph(&resolution)?)
+}
+
+/// Write the lockfile to disk.
+pub(crate) async fn commit(lock: &Lock, workspace: &Workspace) -> Result<(), ProjectError> {
+    let encoded = lock.to_toml()?;
+    fs_err::tokio::write(workspace.install_path().join("uv.lock"), encoded).await?;
+    Ok(())
+}
+
+/// Read the lockfile from the workspace.
+///
+/// Returns `Ok(None)` if the lockfile does not exist.
+pub(crate) async fn read(workspace: &Workspace) -> Result<Option<Lock>, ProjectError> {
+    match fs_err::tokio::read_to_string(&workspace.install_path().join("uv.lock")).await {
+        Ok(encoded) => match toml::from_str::<Lock>(&encoded) {
+            Ok(lock) => Ok(Some(lock)),
+            Err(err) => {
+                eprint!("Failed to parse lockfile; ignoring locked requirements: {err}");
+                Ok(None)
+            }
+        },
+        Err(err) if err.kind() == std::io::ErrorKind::NotFound => Ok(None),
+        Err(err) => Err(err.into()),
+    }
 }
diff --git a/crates/uv/src/commands/project/mod.rs b/crates/uv/src/commands/project/mod.rs
index 5c0f7b833..33cbfec8b 100644
--- a/crates/uv/src/commands/project/mod.rs
+++ b/crates/uv/src/commands/project/mod.rs
@@ -41,6 +41,14 @@ pub(crate) mod tree;
 
 #[derive(thiserror::Error, Debug)]
 pub(crate) enum ProjectError {
+    #[error("The lockfile at `uv.lock` needs to be updated, but `--locked` was provided. To update the lockfile, run `uv lock`.")]
+    LockMismatch,
+
+    #[error(
+        "Unable to find lockfile at `uv.lock`. To create a lockfile, run `uv lock` or `uv sync`."
+    )]
+    MissingLockfile,
+
     #[error("The current Python version ({0}) is not compatible with the locked Python requirement: `{1}`")]
     LockedPythonIncompatibility(Version, RequiresPython),
 
diff --git a/crates/uv/src/commands/project/remove.rs b/crates/uv/src/commands/project/remove.rs
index c9757339f..82be0cfad 100644
--- a/crates/uv/src/commands/project/remove.rs
+++ b/crates/uv/src/commands/project/remove.rs
@@ -11,6 +11,7 @@ use uv_python::{PythonFetch, PythonPreference, PythonRequest};
 use uv_warnings::{warn_user, warn_user_once};
 
 use crate::commands::pip::operations::Modifications;
+use crate::commands::project::lock::commit;
 use crate::commands::{project, ExitStatus, SharedState};
 use crate::printer::Printer;
 use crate::settings::ResolverInstallerSettings;
@@ -98,10 +99,14 @@ pub(crate) async fn remove(
     // Initialize any shared state.
     let state = SharedState::default();
 
-    // Lock and sync the environment.
+    // Read the existing lockfile.
+    let existing = project::lock::read(project.workspace()).await?;
+
+    // Lock and sync the environment, if necessary.
     let lock = project::lock::do_lock(
         project.workspace(),
         venv.interpreter(),
+        existing.as_ref(),
         settings.as_ref().into(),
         &state,
         preview,
@@ -112,6 +117,9 @@ pub(crate) async fn remove(
         printer,
     )
     .await?;
+    if !existing.is_some_and(|existing| existing == lock) {
+        commit(&lock, project.workspace()).await?;
+    }
 
     // Perform a full sync, because we don't know what exactly is affected by the removal.
     // TODO(ibraheem): Should we accept CLI overrides for this? Should we even sync here?
diff --git a/crates/uv/src/commands/project/run.rs b/crates/uv/src/commands/project/run.rs
index f97eb307a..59979db1e 100644
--- a/crates/uv/src/commands/project/run.rs
+++ b/crates/uv/src/commands/project/run.rs
@@ -22,6 +22,7 @@ use uv_python::{
     request_from_version_file, EnvironmentPreference, Interpreter, PythonEnvironment, PythonFetch,
     PythonInstallation, PythonPreference, PythonRequest, VersionRequest,
 };
+
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
 use uv_warnings::warn_user_once;
 
@@ -179,10 +180,14 @@ pub(crate) async fn run(
             )
             .await?;
 
+            // Read the existing lockfile.
+            let existing = project::lock::read(project.workspace()).await?;
+
             // Lock and sync the environment.
             let lock = project::lock::do_lock(
                 project.workspace(),
                 venv.interpreter(),
+                existing.as_ref(),
                 settings.as_ref().into(),
                 &state,
                 preview,
@@ -193,6 +198,11 @@ pub(crate) async fn run(
                 printer,
             )
             .await?;
+
+            if !existing.is_some_and(|existing| existing == lock) {
+                project::lock::commit(&lock, project.workspace()).await?;
+            }
+
             project::sync::do_sync(
                 &project,
                 &venv,
diff --git a/crates/uv/src/commands/project/sync.rs b/crates/uv/src/commands/project/sync.rs
index 443c36ed5..8b2288a07 100644
--- a/crates/uv/src/commands/project/sync.rs
+++ b/crates/uv/src/commands/project/sync.rs
@@ -7,25 +7,30 @@ use uv_dispatch::BuildDispatch;
 use uv_distribution::{VirtualProject, DEV_DEPENDENCIES};
 use uv_installer::SitePackages;
 use uv_python::{PythonEnvironment, PythonFetch, PythonPreference, PythonRequest};
+
 use uv_resolver::{FlatIndex, Lock};
 use uv_types::{BuildIsolation, HashStrategy};
 use uv_warnings::warn_user_once;
 
 use crate::commands::pip::operations::Modifications;
+use crate::commands::project::lock::do_lock;
 use crate::commands::project::{ProjectError, SharedState};
 use crate::commands::{pip, project, ExitStatus};
 use crate::printer::Printer;
-use crate::settings::{InstallerSettings, InstallerSettingsRef};
+use crate::settings::{InstallerSettingsRef, ResolverInstallerSettings};
 
 /// Sync the project environment.
+#[allow(clippy::fn_params_excessive_bools)]
 pub(crate) async fn sync(
+    locked: bool,
+    frozen: bool,
     extras: ExtrasSpecification,
     dev: bool,
     modifications: Modifications,
     python: Option<String>,
     python_preference: PythonPreference,
     python_fetch: PythonFetch,
-    settings: InstallerSettings,
+    settings: ResolverInstallerSettings,
     preview: PreviewMode,
     connectivity: Connectivity,
     concurrency: Concurrency,
@@ -53,12 +58,88 @@ pub(crate) async fn sync(
     )
     .await?;
 
-    // Read the lockfile.
-    let lock: Lock = {
-        let encoded =
-            fs_err::tokio::read_to_string(project.workspace().install_path().join("uv.lock"))
-                .await?;
-        toml::from_str(&encoded)?
+    // Initialize any shared state.
+    let state = SharedState::default();
+
+    let lock = if frozen {
+        // Read the existing lockfile.
+        project::lock::read(project.workspace())
+            .await?
+            .ok_or_else(|| ProjectError::MissingLockfile)?
+    } else if locked {
+        // Read the existing lockfile.
+        let existing = project::lock::read(project.workspace())
+            .await?
+            .ok_or_else(|| ProjectError::MissingLockfile)?;
+
+        // Perform the lock operation, but don't write the lockfile to disk.
+        let lock = match do_lock(
+            project.workspace(),
+            venv.interpreter(),
+            Some(&existing),
+            settings.as_ref().into(),
+            &state,
+            preview,
+            connectivity,
+            concurrency,
+            native_tls,
+            cache,
+            printer,
+        )
+        .await
+        {
+            Ok(lock) => lock,
+            Err(ProjectError::Operation(pip::operations::Error::Resolve(
+                uv_resolver::ResolveError::NoSolution(err),
+            ))) => {
+                let report = miette::Report::msg(format!("{err}"))
+                    .context("No solution found when resolving dependencies:");
+                anstream::eprint!("{report:?}");
+                return Ok(ExitStatus::Failure);
+            }
+            Err(err) => return Err(err.into()),
+        };
+
+        // If the locks disagree, return an error.
+        if lock != existing {
+            return Err(ProjectError::LockMismatch.into());
+        }
+
+        lock
+    } else {
+        // Read the existing lockfile.
+        let existing = project::lock::read(project.workspace()).await?;
+
+        // Perform the lock operation.
+        match do_lock(
+            project.workspace(),
+            venv.interpreter(),
+            existing.as_ref(),
+            settings.as_ref().into(),
+            &state,
+            preview,
+            connectivity,
+            concurrency,
+            native_tls,
+            cache,
+            printer,
+        )
+        .await
+        {
+            Ok(lock) => {
+                project::lock::commit(&lock, project.workspace()).await?;
+                lock
+            }
+            Err(ProjectError::Operation(pip::operations::Error::Resolve(
+                uv_resolver::ResolveError::NoSolution(err),
+            ))) => {
+                let report = miette::Report::msg(format!("{err}"))
+                    .context("No solution found when resolving dependencies:");
+                anstream::eprint!("{report:?}");
+                return Ok(ExitStatus::Failure);
+            }
+            Err(err) => return Err(err.into()),
+        }
     };
 
     // Perform the sync operation.
@@ -69,8 +150,8 @@ pub(crate) async fn sync(
         extras,
         dev,
         modifications,
-        settings.as_ref(),
-        &SharedState::default(),
+        settings.as_ref().into(),
+        &state,
         preview,
         connectivity,
         concurrency,
diff --git a/crates/uv/src/commands/project/tree.rs b/crates/uv/src/commands/project/tree.rs
index 0fa7ec2f3..aae1cdd7b 100644
--- a/crates/uv/src/commands/project/tree.rs
+++ b/crates/uv/src/commands/project/tree.rs
@@ -10,15 +10,15 @@ use uv_client::Connectivity;
 use uv_configuration::{Concurrency, PreviewMode};
 use uv_distribution::Workspace;
 use uv_python::{PythonFetch, PythonPreference, PythonRequest};
+
 use uv_warnings::warn_user_once;
 
 use crate::commands::pip::tree::DisplayDependencyGraph;
 use crate::commands::project::FoundInterpreter;
-use crate::commands::ExitStatus;
+use crate::commands::{project, ExitStatus};
 use crate::printer::Printer;
 use crate::settings::ResolverSettings;
 
-use super::lock::do_lock;
 use super::SharedState;
 
 /// Run a command.
@@ -60,10 +60,14 @@ pub(crate) async fn tree(
     .await?
     .into_interpreter();
 
-    // Update the lock file.
-    let lock = do_lock(
+    // Read the existing lockfile.
+    let existing = project::lock::read(&workspace).await?;
+
+    // Update the lock file, if necessary.
+    let lock = project::lock::do_lock(
         &workspace,
         &interpreter,
+        existing.as_ref(),
         settings.as_ref(),
         &SharedState::default(),
         preview,
@@ -74,6 +78,9 @@ pub(crate) async fn tree(
         printer,
     )
     .await?;
+    if !existing.is_some_and(|existing| existing == lock) {
+        project::lock::commit(&lock, &workspace).await?;
+    }
 
     // Read packages from the lockfile.
     let mut packages: IndexMap<_, Vec<_>> = IndexMap::new();
diff --git a/crates/uv/src/main.rs b/crates/uv/src/main.rs
index aac5b2cbe..14b30151c 100644
--- a/crates/uv/src/main.rs
+++ b/crates/uv/src/main.rs
@@ -884,6 +884,8 @@ async fn run_project(
             let cache = cache.init()?.with_refresh(args.refresh);
 
             commands::sync(
+                args.locked,
+                args.frozen,
                 args.extras,
                 args.dev,
                 args.modifications,
diff --git a/crates/uv/src/settings.rs b/crates/uv/src/settings.rs
index 5e028794a..fc896f108 100644
--- a/crates/uv/src/settings.rs
+++ b/crates/uv/src/settings.rs
@@ -9,7 +9,7 @@ use install_wheel_rs::linker::LinkMode;
 use pep508_rs::{ExtraName, RequirementOrigin};
 use pypi_types::Requirement;
 use uv_cache::{CacheArgs, Refresh};
-use uv_cli::options::{flag, installer_options, resolver_installer_options, resolver_options};
+use uv_cli::options::{flag, resolver_installer_options, resolver_options};
 use uv_cli::{
     AddArgs, ColorChoice, Commands, ExternalCommand, GlobalArgs, ListFormat, LockArgs, Maybe,
     PipCheckArgs, PipCompileArgs, PipFreezeArgs, PipInstallArgs, PipListArgs, PipShowArgs,
@@ -29,8 +29,7 @@ use uv_python::{Prefix, PythonFetch, PythonPreference, PythonVersion, Target};
 use uv_requirements::RequirementsSource;
 use uv_resolver::{AnnotationStyle, DependencyMode, ExcludeNewer, PreReleaseMode, ResolutionMode};
 use uv_settings::{
-    Combine, FilesystemOptions, InstallerOptions, Options, PipOptions, ResolverInstallerOptions,
-    ResolverOptions,
+    Combine, FilesystemOptions, Options, PipOptions, ResolverInstallerOptions, ResolverOptions,
 };
 
 use crate::commands::pip::operations::Modifications;
@@ -415,12 +414,14 @@ impl PythonFindSettings {
 #[allow(clippy::struct_excessive_bools, dead_code)]
 #[derive(Debug, Clone)]
 pub(crate) struct SyncSettings {
+    pub(crate) locked: bool,
+    pub(crate) frozen: bool,
     pub(crate) extras: ExtrasSpecification,
     pub(crate) dev: bool,
     pub(crate) modifications: Modifications,
     pub(crate) python: Option<String>,
     pub(crate) refresh: Refresh,
-    pub(crate) settings: InstallerSettings,
+    pub(crate) settings: ResolverInstallerSettings,
 }
 
 impl SyncSettings {
@@ -428,6 +429,8 @@ impl SyncSettings {
     #[allow(clippy::needless_pass_by_value)]
     pub(crate) fn resolve(args: SyncArgs, filesystem: Option<FilesystemOptions>) -> Self {
         let SyncArgs {
+            locked,
+            frozen,
             extra,
             all_extras,
             no_all_extras,
@@ -447,6 +450,8 @@ impl SyncSettings {
         };
 
         Self {
+            locked,
+            frozen,
             extras: ExtrasSpecification::from_args(
                 flag(all_extras, no_all_extras).unwrap_or_default(),
                 extra.unwrap_or_default(),
@@ -455,7 +460,10 @@ impl SyncSettings {
             modifications,
             python,
             refresh: Refresh::from(refresh),
-            settings: InstallerSettings::combine(installer_options(installer, build), filesystem),
+            settings: ResolverInstallerSettings::combine(
+                resolver_installer_options(installer, build),
+                filesystem,
+            ),
         }
     }
 }
@@ -1272,20 +1280,6 @@ impl VenvSettings {
 ///
 /// Combines the `[tool.uv]` persistent configuration with the command-line arguments
 /// ([`InstallerArgs`], represented as [`InstallerOptions`]).
-#[allow(clippy::struct_excessive_bools)]
-#[derive(Debug, Clone, Default)]
-pub(crate) struct InstallerSettings {
-    pub(crate) index_locations: IndexLocations,
-    pub(crate) index_strategy: IndexStrategy,
-    pub(crate) keyring_provider: KeyringProviderType,
-    pub(crate) config_setting: ConfigSettings,
-    pub(crate) exclude_newer: Option<ExcludeNewer>,
-    pub(crate) link_mode: LinkMode,
-    pub(crate) compile_bytecode: bool,
-    pub(crate) reinstall: Reinstall,
-    pub(crate) build_options: BuildOptions,
-}
-
 #[derive(Debug, Clone)]
 pub(crate) struct InstallerSettingsRef<'a> {
     pub(crate) index_locations: &'a IndexLocations,
@@ -1299,100 +1293,6 @@ pub(crate) struct InstallerSettingsRef<'a> {
     pub(crate) build_options: &'a BuildOptions,
 }
 
-impl InstallerSettings {
-    /// Resolve the [`InstallerSettings`] from the CLI and filesystem configuration.
-    pub(crate) fn combine(args: InstallerOptions, filesystem: Option<FilesystemOptions>) -> Self {
-        let ResolverInstallerOptions {
-            index_url,
-            extra_index_url,
-            no_index,
-            find_links,
-            index_strategy,
-            keyring_provider,
-            resolution: _,
-            prerelease: _,
-            config_settings,
-            exclude_newer,
-            link_mode,
-            compile_bytecode,
-            upgrade: _,
-            upgrade_package: _,
-            reinstall,
-            reinstall_package,
-            no_build,
-            no_build_package,
-            no_binary,
-            no_binary_package,
-        } = filesystem
-            .map(FilesystemOptions::into_options)
-            .map(|options| options.top_level)
-            .unwrap_or_default();
-
-        Self {
-            index_locations: IndexLocations::new(
-                args.index_url.combine(index_url),
-                args.extra_index_url
-                    .combine(extra_index_url)
-                    .unwrap_or_default(),
-                args.find_links.combine(find_links).unwrap_or_default(),
-                args.no_index.combine(no_index).unwrap_or_default(),
-            ),
-            index_strategy: args
-                .index_strategy
-                .combine(index_strategy)
-                .unwrap_or_default(),
-            keyring_provider: args
-                .keyring_provider
-                .combine(keyring_provider)
-                .unwrap_or_default(),
-            config_setting: args
-                .config_settings
-                .combine(config_settings)
-                .unwrap_or_default(),
-            exclude_newer: args.exclude_newer.combine(exclude_newer),
-            link_mode: args.link_mode.combine(link_mode).unwrap_or_default(),
-            compile_bytecode: args
-                .compile_bytecode
-                .combine(compile_bytecode)
-                .unwrap_or_default(),
-            reinstall: Reinstall::from_args(
-                args.reinstall.combine(reinstall),
-                args.reinstall_package
-                    .combine(reinstall_package)
-                    .unwrap_or_default(),
-            ),
-            build_options: BuildOptions::new(
-                NoBinary::from_args(
-                    args.no_binary.combine(no_binary),
-                    args.no_binary_package
-                        .combine(no_binary_package)
-                        .unwrap_or_default(),
-                ),
-                NoBuild::from_args(
-                    args.no_build.combine(no_build),
-                    args.no_build_package
-                        .combine(no_build_package)
-                        .unwrap_or_default(),
-                ),
-            ),
-        }
-    }
-
-    pub(crate) fn as_ref(&self) -> InstallerSettingsRef {
-        InstallerSettingsRef {
-            index_locations: &self.index_locations,
-            index_strategy: self.index_strategy,
-            keyring_provider: self.keyring_provider,
-            config_setting: &self.config_setting,
-            exclude_newer: self.exclude_newer,
-            link_mode: self.link_mode,
-            compile_bytecode: self.compile_bytecode,
-            reinstall: &self.reinstall,
-            build_options: &self.build_options,
-        }
-    }
-}
-
 /// The resolved settings to use for an invocation of the `uv` CLI when resolving dependencies.
 ///
 /// Combines the `[tool.uv]` persistent configuration with the command-line arguments
diff --git a/crates/uv/tests/edit.rs b/crates/uv/tests/edit.rs
index 12ccccc14..660643dc1 100644
--- a/crates/uv/tests/edit.rs
+++ b/crates/uv/tests/edit.rs
@@ -112,7 +112,7 @@ fn add_registry() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -149,7 +149,7 @@ fn add_git() -> Result<()> {
     Resolved 4 packages in [TIME]
     "###);
 
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -270,7 +270,7 @@ fn add_git() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -307,7 +307,7 @@ fn add_git_raw() -> Result<()> {
     Resolved 4 packages in [TIME]
     "###);
 
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -416,7 +416,7 @@ fn add_git_raw() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -506,7 +506,7 @@ fn add_unnamed() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -626,7 +626,7 @@ fn add_remove_dev() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -705,7 +705,7 @@ fn add_remove_dev() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -786,7 +786,7 @@ fn add_remove_optional() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -862,7 +862,7 @@ fn add_remove_optional() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -993,7 +993,7 @@ fn add_remove_workspace() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().current_dir(&child1), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").current_dir(&child1), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1062,7 +1062,7 @@ fn add_remove_workspace() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().current_dir(&child1), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").current_dir(&child1), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1173,7 +1173,7 @@ fn add_workspace_editable() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().current_dir(&child1), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").current_dir(&child1), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1212,7 +1212,7 @@ fn update() -> Result<()> {
     Resolved 6 packages in [TIME]
     "###);
 
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1451,7 +1451,7 @@ fn update() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1490,7 +1490,7 @@ fn add_no_clean() -> Result<()> {
     Resolved 4 packages in [TIME]
     "###);
 
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1579,7 +1579,7 @@ fn add_no_clean() -> Result<()> {
     });
 
     // Install from the lockfile without cleaning the environment.
-    uv_snapshot!(context.filters(), context.sync().arg("--no-clean"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").arg("--no-clean"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1590,7 +1590,7 @@ fn add_no_clean() -> Result<()> {
     "###);
 
     // Install from the lockfile, cleaning the environment.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1630,7 +1630,7 @@ fn remove_registry() -> Result<()> {
     Resolved 4 packages in [TIME]
     "###);
 
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1698,7 +1698,7 @@ fn remove_registry() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
diff --git a/crates/uv/tests/lock.rs b/crates/uv/tests/lock.rs
index 2949a6797..14dff499f 100644
--- a/crates/uv/tests/lock.rs
+++ b/crates/uv/tests/lock.rs
@@ -88,7 +88,7 @@ fn lock_wheel_registry() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -160,7 +160,7 @@ fn lock_sdist_registry() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().env_remove("UV_EXCLUDE_NEWER"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").env_remove("UV_EXCLUDE_NEWER"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -229,7 +229,7 @@ fn lock_sdist_git() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -323,7 +323,7 @@ fn lock_wheel_url() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -417,7 +417,7 @@ fn lock_sdist_url() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -531,7 +531,7 @@ fn lock_project_extra() -> Result<()> {
     });
 
     // Install the base dependencies from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -547,7 +547,7 @@ fn lock_project_extra() -> Result<()> {
     "###);
 
     // Install the extras from the lockfile.
-    uv_snapshot!(context.filters(), context.sync().arg("--extra").arg("test"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").arg("--extra").arg("test"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -591,7 +591,7 @@ fn lock_project_with_overrides() -> Result<()> {
     "###);
 
     // Install the base dependencies from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -772,7 +772,7 @@ fn lock_dependency_extra() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -998,7 +998,7 @@ fn lock_conditional_dependency_extra() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1022,7 +1022,7 @@ fn lock_conditional_dependency_extra() -> Result<()> {
     fs_err::copy(lockfile, context_38.temp_dir.join("uv.lock"))?;
 
     // Install from the lockfile.
-    uv_snapshot!(context_38.filters(), context_38.sync(), @r###"
+    uv_snapshot!(context_38.filters(), context_38.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1189,7 +1189,7 @@ fn lock_dependency_non_existent_extra() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1943,7 +1943,7 @@ fn lock_requires_python() -> Result<()> {
 
     // Install from the lockfile.
     // Note we need to disable Python fetches or we'll just download 3.12
-    uv_snapshot!(filters, context38.sync().arg("--python-fetch").arg("manual"), @r###"
+    uv_snapshot!(filters, context38.sync().arg("--frozen").arg("--python-fetch").arg("manual"), @r###"
     success: false
     exit_code: 2
     ----- stdout -----
@@ -2398,7 +2398,7 @@ fn lock_dev() -> Result<()> {
     });
 
     // Install from the lockfile, excluding development dependencies.
-    uv_snapshot!(context.filters(), context.sync().arg("--no-dev"), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").arg("--no-dev"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -2412,7 +2412,7 @@ fn lock_dev() -> Result<()> {
     "###);
 
     // Install from the lockfile, including development dependencies (the default).
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -2806,7 +2806,7 @@ fn lock_cycles() -> Result<()> {
     });
 
     // Install from the lockfile.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
diff --git a/crates/uv/tests/sync.rs b/crates/uv/tests/sync.rs
new file mode 100644
index 000000000..ee28786d6
--- /dev/null
+++ b/crates/uv/tests/sync.rs
@@ -0,0 +1,164 @@
+#![cfg(all(feature = "python", feature = "pypi"))]
+
+use anyhow::Result;
+use assert_cmd::prelude::*;
+use assert_fs::prelude::*;
+
+use common::{uv_snapshot, TestContext};
+
+mod common;
+
+#[test]
+fn sync() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+        "#,
+    )?;
+
+    // Running `uv sync` should generate a lockfile.
+    uv_snapshot!(context.filters(), context.sync(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning.
+    Resolved 2 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + iniconfig==2.0.0
+     + project==0.1.0 (from file://[TEMP_DIR]/)
+    "###);
+
+    assert!(context.temp_dir.child("uv.lock").exists());
+
+    Ok(())
+}
+
+#[test]
+fn locked() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==3.7.0"]
+        "#,
+    )?;
+
+    // Running with `--locked` should error, if no lockfile is present.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning.
+    error: Unable to find lockfile at `uv.lock`. To create a lockfile, run `uv lock` or `uv sync`.
+    "###);
+
+    // Lock the initial requirements.
+    context.lock().assert().success();
+
+    let existing = fs_err::read_to_string(context.temp_dir.child("uv.lock"))?;
+
+    // Update the requirements.
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+        "#,
+    )?;
+
+    // Running with `--locked` should error.
+    uv_snapshot!(context.filters(), context.sync().arg("--locked"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning.
+    Resolved 2 packages in [TIME]
+    error: The lockfile at `uv.lock` needs to be updated, but `--locked` was provided. To update the lockfile, run `uv lock`.
+    "###);
+
+    let updated = fs_err::read_to_string(context.temp_dir.child("uv.lock"))?;
+
+    // And the lockfile should be unchanged.
+    assert_eq!(existing, updated);
+
+    Ok(())
+}
+
+#[test]
+fn frozen() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==3.7.0"]
+        "#,
+    )?;
+
+    // Running with `--frozen` should error, if no lockfile is present.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning.
+    error: Unable to find lockfile at `uv.lock`. To create a lockfile, run `uv lock` or `uv sync`.
+    "###);
+
+    context.lock().assert().success();
+
+    // Update the requirements.
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+        "#,
+    )?;
+
+    // Running with `--frozen` should install the stale lockfile.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv sync` is experimental and may change without warning.
+    Prepared 4 packages in [TIME]
+    Installed 4 packages in [TIME]
+     + anyio==3.7.0
+     + idna==3.6
+     + project==0.1.0 (from file://[TEMP_DIR]/)
+     + sniffio==1.3.1
+    "###);
+
+    Ok(())
+}