diff --git a/codex-rs/app-server-protocol/src/bin/write_schema_fixtures.rs b/codex-rs/app-server-protocol/src/bin/write_schema_fixtures.rs
index a8e36d1ee89..789d30cea20 100644
--- a/codex-rs/app-server-protocol/src/bin/write_schema_fixtures.rs
+++ b/codex-rs/app-server-protocol/src/bin/write_schema_fixtures.rs
@@ -13,6 +13,10 @@ struct Args {
     /// Optional path to the Prettier executable to format generated TypeScript files.
     #[arg(short = 'p', long = "prettier", value_name = "PRETTIER_BIN")]
     prettier: Option<PathBuf>,
+
+    /// Include experimental API methods and fields in generated fixtures.
+    #[arg(long = "experimental")]
+    experimental: bool,
 }
 
 fn main() -> Result<()> {
@@ -22,11 +26,17 @@ fn main() -> Result<()> {
         .schema_root
         .unwrap_or_else(|| PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("schema"));
 
-    codex_app_server_protocol::write_schema_fixtures(&schema_root, args.prettier.as_deref())
-        .with_context(|| {
-            format!(
-                "failed to regenerate schema fixtures under {}",
-                schema_root.display()
-            )
-        })
+    codex_app_server_protocol::write_schema_fixtures_with_options(
+        &schema_root,
+        args.prettier.as_deref(),
+        codex_app_server_protocol::SchemaFixtureOptions {
+            experimental_api: args.experimental,
+        },
+    )
+    .with_context(|| {
+        format!(
+            "failed to regenerate schema fixtures under {}",
+            schema_root.display()
+        )
+    })
 }
diff --git a/codex-rs/app-server-protocol/src/lib.rs b/codex-rs/app-server-protocol/src/lib.rs
index 7b3f17045b0..54a933bb748 100644
--- a/codex-rs/app-server-protocol/src/lib.rs
+++ b/codex-rs/app-server-protocol/src/lib.rs
@@ -16,5 +16,7 @@ pub use protocol::common::*;
 pub use protocol::thread_history::*;
 pub use protocol::v1::*;
 pub use protocol::v2::*;
+pub use schema_fixtures::SchemaFixtureOptions;
 pub use schema_fixtures::read_schema_fixture_tree;
 pub use schema_fixtures::write_schema_fixtures;
+pub use schema_fixtures::write_schema_fixtures_with_options;
diff --git a/codex-rs/app-server-protocol/src/schema_fixtures.rs b/codex-rs/app-server-protocol/src/schema_fixtures.rs
index efd8bb2cb01..918011e95cd 100644
--- a/codex-rs/app-server-protocol/src/schema_fixtures.rs
+++ b/codex-rs/app-server-protocol/src/schema_fixtures.rs
@@ -6,6 +6,11 @@ use std::collections::BTreeMap;
 use std::path::Path;
 use std::path::PathBuf;
 
+#[derive(Clone, Copy, Debug, Default)]
+pub struct SchemaFixtureOptions {
+    pub experimental_api: bool,
+}
+
 pub fn read_schema_fixture_tree(schema_root: &Path) -> Result<BTreeMap<PathBuf, Vec<u8>>> {
     let typescript_root = schema_root.join("typescript");
     let json_root = schema_root.join("json");
@@ -26,14 +31,30 @@ pub fn read_schema_fixture_tree(schema_root: &Path) -> Result<BTreeMap<PathBuf,
 /// This is intended to be used by tooling (e.g., `just write-app-server-schema`).
 /// It deletes any previously generated files so stale artifacts are removed.
 pub fn write_schema_fixtures(schema_root: &Path, prettier: Option<&Path>) -> Result<()> {
+    write_schema_fixtures_with_options(schema_root, prettier, SchemaFixtureOptions::default())
+}
+
+/// Regenerates schema fixtures with configurable options.
+pub fn write_schema_fixtures_with_options(
+    schema_root: &Path,
+    prettier: Option<&Path>,
+    options: SchemaFixtureOptions,
+) -> Result<()> {
     let typescript_out_dir = schema_root.join("typescript");
     let json_out_dir = schema_root.join("json");
 
     ensure_empty_dir(&typescript_out_dir)?;
     ensure_empty_dir(&json_out_dir)?;
 
-    crate::generate_ts(&typescript_out_dir, prettier)?;
-    crate::generate_json(&json_out_dir)?;
+    crate::generate_ts_with_options(
+        &typescript_out_dir,
+        prettier,
+        crate::GenerateTsOptions {
+            experimental_api: options.experimental_api,
+            ..crate::GenerateTsOptions::default()
+        },
+    )?;
+    crate::generate_json_with_experimental(&json_out_dir, options.experimental_api)?;
 
     Ok(())
 }
diff --git a/codex-rs/app-server/README.md b/codex-rs/app-server/README.md
index 67bb36d1498..1d5b6d15fd9 100644
--- a/codex-rs/app-server/README.md
+++ b/codex-rs/app-server/README.md
@@ -788,6 +788,8 @@ At runtime, clients must send `initialize` with `capabilities.experimentalApi =
 
    ```bash
    just write-app-server-schema
+   # Include experimental API fields/methods in fixtures.
+   just write-app-server-schema --experimental
    ```
     
 5. Verify the protocol crate:
diff --git a/justfile b/justfile
index 67577c7c7ff..024a31ba2a7 100644
--- a/justfile
+++ b/justfile
@@ -69,8 +69,8 @@ write-config-schema:
     cargo run -p codex-core --bin codex-write-config-schema
 
 # Regenerate vendored app-server protocol schema artifacts.
-write-app-server-schema:
-    cargo run -p codex-app-server-protocol --bin write_schema_fixtures
+write-app-server-schema *args:
+    cargo run -p codex-app-server-protocol --bin write_schema_fixtures -- "$@"
 
 # Tail logs from the state SQLite database
 log *args: