diff --git a/crates/pack-core/src/client/context.rs b/crates/pack-core/src/client/context.rs
index 08e0ac676..476d307c3 100644
--- a/crates/pack-core/src/client/context.rs
+++ b/crates/pack-core/src/client/context.rs
@@ -7,6 +7,7 @@ use turbo_tasks::{
     FxIndexMap, ResolvedVc, TaskInput, TryJoinIterExt, ValueToString, Vc, trace::TraceRawVcs,
 };
 use turbo_tasks_env::EnvMap;
+use turbo_tasks_fs::File;
 use turbo_tasks_fs::FileSystemPath;
 use turbopack::{
     css::chunk::CssChunkType,
@@ -18,6 +19,7 @@ use turbopack::{
 };
 use turbopack_browser::{BrowserChunkingContext, CurrentChunkMethod};
 use turbopack_core::{
+    asset::AssetContent,
     chunk::{
         ChunkingConfig, ChunkingContext, MangleType, MinifyType, SourceMapSourceType,
         SourceMapsType, module_id_strategies::ModuleIdStrategy,
@@ -30,6 +32,7 @@ use turbopack_core::{
     file_source::FileSource,
     free_var_references,
     module_graph::export_usage::OptionExportUsageInfo,
+    virtual_source::VirtualSource,
 };
 use turbopack_ecmascript::{TypeofWindow, chunk::EcmascriptChunkType};
 use turbopack_node::{
@@ -212,6 +215,34 @@ pub async fn get_client_runtime_entries(
     let watch = *watch.await?;
     let hot = *hot.await?;
 
+    // Add runtime bootstrap code if configured
+    // This runs synchronously in the runtime chunk before any entry modules execute
+    let bootstrap_config_opt = config.runtime_bootstrap().await?;
+    if let Some(bootstrap_config) = bootstrap_config_opt.as_ref() {
+        match bootstrap_config {
+            crate::config::RuntimeBootstrapConfig::Code(code) => {
+                // Inline code: create a virtual source
+                let bootstrap_source = VirtualSource::new(
+                    project_root.join("__runtime_bootstrap__.js")?,
+                    AssetContent::file(File::from(code.clone()).into()),
+                )
+                .to_resolved()
+                .await?;
+                runtime_entries.push(
+                    RuntimeEntry::Source(ResolvedVc::upcast(bootstrap_source)).resolved_cell(),
+                );
+            }
+            crate::config::RuntimeBootstrapConfig::Path(path) => {
+                // File path: use FileSource to load the file
+                let bootstrap_path = project_root.join(path.as_str())?;
+                let bootstrap_source = FileSource::new(bootstrap_path).to_resolved().await?;
+                runtime_entries.push(
+                    RuntimeEntry::Source(ResolvedVc::upcast(bootstrap_source)).resolved_cell(),
+                );
+            }
+        }
+    }
+
     if is_development && watch {
         let enable_react_refresh =
             assert_can_resolve_react_refresh(project_root.clone(), resolve_options_context)
diff --git a/crates/pack-core/src/config.rs b/crates/pack-core/src/config.rs
index 454426726..6f7af3119 100644
--- a/crates/pack-core/src/config.rs
+++ b/crates/pack-core/src/config.rs
@@ -120,6 +120,21 @@ pub enum ProviderConfigValue {
 #[turbo_tasks::value(transparent)]
 pub struct ProviderConfig(FxIndexMap<RcStr, ProviderConfigValue>);
 
+/// Runtime bootstrap configuration - can be either inline code or a file path
+#[derive(
+    Clone, Debug, PartialEq, Eq, Serialize, Deserialize, TraceRawVcs, NonLocalValue, OperationValue,
+)]
+#[serde(untagged)]
+pub enum RuntimeBootstrapConfig {
+    /// Inline JavaScript code
+    Code(RcStr),
+    /// Path to a JavaScript/TypeScript file
+    Path(RcStr),
+}
+
+#[turbo_tasks::value(transparent)]
+pub struct OptionRuntimeBootstrapConfig(Option<RuntimeBootstrapConfig>);
+
 #[turbo_tasks::value(serialization = "custom", eq = "manual")]
 #[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize, OperationValue)]
 #[serde(rename_all = "camelCase")]
@@ -142,6 +157,7 @@ pub struct Config {
     cache_handler: Option<RcStr>,
     node_polyfill: Option<bool>,
     dev_server: Option<DevServer>,
+    runtime_bootstrap: Option<RuntimeBootstrapConfig>,
     #[serde(default)]
     experimental: ExperimentalConfig,
     #[cfg(feature = "test")]
@@ -1191,6 +1207,11 @@ impl Config {
         Vc::cell(self.node_polyfill.unwrap_or(false))
     }
 
+    #[turbo_tasks::function]
+    pub fn runtime_bootstrap(&self) -> Vc<OptionRuntimeBootstrapConfig> {
+        OptionRuntimeBootstrapConfig(self.runtime_bootstrap.clone()).cell()
+    }
+
     #[turbo_tasks::function]
     pub async fn import_externals(&self) -> Result<Vc<bool>> {
         Ok(Vc::cell(match self.experimental.esm_externals {