From 431f96572e82c3c2ef950ffc0483b112a972d506 Mon Sep 17 00:00:00 2001
From: Yuval Tassa <tassa@google.com>
Date: Mon, 6 Oct 2025 02:50:09 -0700
Subject: [PATCH] Remove unused `mjOption.apirate`.

PiperOrigin-RevId: 815633571
Change-Id: Ib98f3eb2df47f96fa1fe6e987a3a0cd23a9479f6
---
 doc/XMLreference.rst                          |  7 ------
 doc/XMLschema.rst                             | 14 +++++------
 doc/changelog.rst                             |  8 +++---
 doc/includes/references.h                     |  1 -
 .../experimental/usd/mjcPhysics/sceneAPI.h    | 25 -------------------
 .../experimental/usd/mjcPhysics/tokens.h      |  4 ---
 include/mujoco/mjmodel.h                      |  1 -
 include/mujoco/mjxmacro.h                     |  1 -
 mjx/mujoco/mjx/_src/io_test.py                |  2 +-
 mjx/mujoco/mjx/_src/types.py                  |  1 -
 python/mujoco/introspect/structs.py           |  5 ----
 simulate/simulate.cc                          |  1 -
 src/engine/engine_init.c                      |  1 -
 src/experimental/studio/app.cc                |  1 -
 .../usd/mjcPhysics/generatedSchema.usda       |  5 ----
 src/experimental/usd/mjcPhysics/sceneAPI.cpp  | 12 ---------
 src/experimental/usd/mjcPhysics/schema.usda   |  9 -------
 src/experimental/usd/mjcPhysics/tokens.cpp    |  2 --
 .../usd/plugins/mjcf/mujoco_to_usd.cc         |  1 -
 src/experimental/usd/usd_to_mjspec.cc         |  4 ---
 src/xml/xml_native_reader.cc                  |  5 ++--
 src/xml/xml_native_writer.cc                  |  1 -
 .../usd/mjcPhysics/mjc_physics_scene_test.cc  |  1 -
 .../usd/plugins/mjcf/mjcf_file_format_test.cc | 13 ----------
 unity/Runtime/Bindings/MjBindings.cs          |  1 -
 unity/Runtime/Components/MjGlobalSettings.cs  |  1 -
 26 files changed, 15 insertions(+), 112 deletions(-)

diff --git a/doc/XMLreference.rst b/doc/XMLreference.rst
index 9005f2f5..c49eee0a 100644
--- a/doc/XMLreference.rst
+++ b/doc/XMLreference.rst
@@ -308,13 +308,6 @@ adjust it properly through the XML.
    optimization-related applications, real-time is no longer good enough and instead it is desirable to run the
    simulation as fast as possible. In that case the time step should be made as large as possible.
 
-.. _option-apirate:
-
-:at:`apirate`: :at-val:`real, "100"`
-   This parameter determines the rate (in Hz) at which an external API allows the update function to be executed. This
-   mechanism is used to simulate devices with limited communication bandwidth. It only affects the socket API and not
-   the physics simulation.
-
 .. _option-impratio:
 
 :at:`impratio`: :at-val:`real, "1"`
diff --git a/doc/XMLschema.rst b/doc/XMLschema.rst
index 538e1b62..9651628d 100644
--- a/doc/XMLschema.rst
+++ b/doc/XMLschema.rst
@@ -10,19 +10,19 @@
 | :ref:`option                       | \* |    :class: mjcf-attributes                                                                                                                                                                                                                                                   |
 | <option>`                          |    |                                                                                                                                                                                                                                                                              |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`timestep<option-timestep>`                                | :ref:`apirate<option-apirate>`                                  | :ref:`impratio<option-impratio>`                                | :ref:`tolerance<option-tolerance>`                              | |
+|                                    |    |    | :ref:`timestep<option-timestep>`                                | :ref:`impratio<option-impratio>`                                | :ref:`tolerance<option-tolerance>`                              | :ref:`ls_tolerance<option-ls_tolerance>`                        | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`ls_tolerance<option-ls_tolerance>`                        | :ref:`noslip_tolerance<option-noslip_tolerance>`                | :ref:`ccd_tolerance<option-ccd_tolerance>`                      | :ref:`gravity<option-gravity>`                                  | |
+|                                    |    |    | :ref:`noslip_tolerance<option-noslip_tolerance>`                | :ref:`ccd_tolerance<option-ccd_tolerance>`                      | :ref:`gravity<option-gravity>`                                  | :ref:`wind<option-wind>`                                        | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`wind<option-wind>`                                        | :ref:`magnetic<option-magnetic>`                                | :ref:`density<option-density>`                                  | :ref:`viscosity<option-viscosity>`                              | |
+|                                    |    |    | :ref:`magnetic<option-magnetic>`                                | :ref:`density<option-density>`                                  | :ref:`viscosity<option-viscosity>`                              | :ref:`o_margin<option-o_margin>`                                | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`o_margin<option-o_margin>`                                | :ref:`o_solref<option-o_solref>`                                | :ref:`o_solimp<option-o_solimp>`                                | :ref:`o_friction<option-o_friction>`                            | |
+|                                    |    |    | :ref:`o_solref<option-o_solref>`                                | :ref:`o_solimp<option-o_solimp>`                                | :ref:`o_friction<option-o_friction>`                            | :ref:`integrator<option-integrator>`                            | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`integrator<option-integrator>`                            | :ref:`cone<option-cone>`                                        | :ref:`jacobian<option-jacobian>`                                | :ref:`solver<option-solver>`                                    | |
+|                                    |    |    | :ref:`cone<option-cone>`                                        | :ref:`jacobian<option-jacobian>`                                | :ref:`solver<option-solver>`                                    | :ref:`iterations<option-iterations>`                            | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`iterations<option-iterations>`                            | :ref:`ls_iterations<option-ls_iterations>`                      | :ref:`noslip_iterations<option-noslip_iterations>`              | :ref:`ccd_iterations<option-ccd_iterations>`                    | |
+|                                    |    |    | :ref:`ls_iterations<option-ls_iterations>`                      | :ref:`noslip_iterations<option-noslip_iterations>`              | :ref:`ccd_iterations<option-ccd_iterations>`                    | :ref:`sdf_iterations<option-sdf_iterations>`                    | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`sdf_iterations<option-sdf_iterations>`                    | :ref:`sdf_initpoints<option-sdf_initpoints>`                    | :ref:`actuatorgroupdisable<option-actuatorgroupdisable>`        |                                                                 | |
+|                                    |    |    | :ref:`sdf_initpoints<option-sdf_initpoints>`                    | :ref:`actuatorgroupdisable<option-actuatorgroupdisable>`        |                                                                 |                                                                 | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 +------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 | |_| option |br| |_| |L|            |    | .. table::                                                                                                                                                                                                                                                                   |
diff --git a/doc/changelog.rst b/doc/changelog.rst
index b38e1b03..db74d707 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -23,17 +23,19 @@ General
   limit, are recolored by using the :ref:`constraint impedance<soParameters>` :math:`d` to mix the existing color with
   :ref:`visual/rgba/constraint<visual-rgba-constraint>`. For spatial tendons, this visualization aid is active only if
   no :ref:`material<tendon-spatial-material>` is set and :ref:`rgba<tendon-spatial-rgba>` is default.
-
 - Added :ref:`mju_getXMLDependencies` for computing a list of unique asset dependencies from an MJCF file.
-
 - Added the code sample ``dependencies`` which provides command line utility for printing the result of :ref:`mju_getXMLDependencies`.
 
+.. admonition:: Breaking ABI changes
+   :class: attention
+
+   - The attribute ``mjOption.apirate`` was unused and has been removed.
 
 MJX
 ^^^
-
 - Fix :github:issue:`2508`, ``qLD`` shapes mismatched mjModel during ``get_data_into``.
 
+
 Version 3.3.6 (September 15, 2025)
 ----------------------------------
 
diff --git a/doc/includes/references.h b/doc/includes/references.h
index 31b8d118..7f7f4be6 100644
--- a/doc/includes/references.h
+++ b/doc/includes/references.h
@@ -800,7 +800,6 @@ typedef struct mjVFS_ mjVFS;
 struct mjOption_ {                // physics options
   // timing parameters
   mjtNum timestep;                // timestep
-  mjtNum apirate;                 // update rate for remote API (Hz)
 
   // solver parameters
   mjtNum impratio;                // ratio of friction-to-normal contact impedance
diff --git a/include/mujoco/experimental/usd/mjcPhysics/sceneAPI.h b/include/mujoco/experimental/usd/mjcPhysics/sceneAPI.h
index bd694827..e91abe51 100644
--- a/include/mujoco/experimental/usd/mjcPhysics/sceneAPI.h
+++ b/include/mujoco/experimental/usd/mjcPhysics/sceneAPI.h
@@ -170,31 +170,6 @@ class MjcPhysicsSceneAPI : public UsdAPISchemaBase {
   UsdAttribute CreateTimestepAttr(VtValue const& defaultValue = VtValue(),
                                   bool writeSparsely = false) const;
 
- public:
-  // --------------------------------------------------------------------- //
-  // APIRATE
-  // --------------------------------------------------------------------- //
-  /// Determines the rate (in Hz) at which an external API allows
-  /// the update function to be executed.
-  ///
-  /// | ||
-  /// | -- | -- |
-  /// | Declaration | `uniform double mjc:option:apirate = 100` |
-  /// | C++ Type | double |
-  /// | \ref Usd_Datatypes "Usd Type" | SdfValueTypeNames->Double |
-  /// | \ref SdfVariability "Variability" | SdfVariabilityUniform |
-  MJCPHYSICS_API
-  UsdAttribute GetApiRateAttr() const;
-
-  /// See GetApiRateAttr(), and also
-  /// \ref Usd_Create_Or_Get_Property for when to use Get vs Create.
-  /// If specified, author \p defaultValue as the attribute's default,
-  /// sparsely (when it makes sense to do so) if \p writeSparsely is \c true -
-  /// the default for \p writeSparsely is \c false.
-  MJCPHYSICS_API
-  UsdAttribute CreateApiRateAttr(VtValue const& defaultValue = VtValue(),
-                                 bool writeSparsely = false) const;
-
  public:
   // --------------------------------------------------------------------- //
   // IMPRATIO
diff --git a/include/mujoco/experimental/usd/mjcPhysics/tokens.h b/include/mujoco/experimental/usd/mjcPhysics/tokens.h
index 855e36bf..7927fb69 100644
--- a/include/mujoco/experimental/usd/mjcPhysics/tokens.h
+++ b/include/mujoco/experimental/usd/mjcPhysics/tokens.h
@@ -455,10 +455,6 @@ struct MjcPhysicsTokensType {
   ///
   /// MjcPhysicsSceneAPI
   const TfToken mjcOptionActuatorgroupdisable;
-  /// \brief "mjc:option:apirate"
-  ///
-  /// MjcPhysicsSceneAPI
-  const TfToken mjcOptionApirate;
   /// \brief "mjc:option:ccd_iterations"
   ///
   /// MjcPhysicsSceneAPI
diff --git a/include/mujoco/mjmodel.h b/include/mujoco/mjmodel.h
index 17d42a66..a33f148d 100644
--- a/include/mujoco/mjmodel.h
+++ b/include/mujoco/mjmodel.h
@@ -469,7 +469,6 @@ typedef struct mjVFS_ mjVFS;
 struct mjOption_ {                // physics options
   // timing parameters
   mjtNum timestep;                // timestep
-  mjtNum apirate;                 // update rate for remote API (Hz)
 
   // solver parameters
   mjtNum impratio;                // ratio of friction-to-normal contact impedance
diff --git a/include/mujoco/mjxmacro.h b/include/mujoco/mjxmacro.h
index d2ba7e95..06427085 100644
--- a/include/mujoco/mjxmacro.h
+++ b/include/mujoco/mjxmacro.h
@@ -21,7 +21,6 @@
 // scalar fields of mjOption
 #define MJOPTION_FLOATS             \
     X( mjtNum,  timestep         )  \
-    X( mjtNum,  apirate          )  \
     X( mjtNum,  impratio         )  \
     X( mjtNum,  tolerance        )  \
     X( mjtNum,  ls_tolerance     )  \
diff --git a/mjx/mujoco/mjx/_src/io_test.py b/mjx/mujoco/mjx/_src/io_test.py
index fb7eafe2..4b8e0703 100644
--- a/mjx/mujoco/mjx/_src/io_test.py
+++ b/mjx/mujoco/mjx/_src/io_test.py
@@ -173,7 +173,7 @@ class ModelIOTest(parameterized.TestCase):
       self.assertFalse(hasattr(mx, 'bvh_aabb'))
     elif impl == 'c':
       # Options specific to C are populated.
-      self.assertEqual(mx.opt._impl.apirate, m.opt.apirate)
+      self.assertEqual(mx.opt._impl.noslip_iterations, m.opt.noslip_iterations)
       # Fields private to C backend impl are populated.
       self.assertTrue(hasattr(mx._impl, 'bvh_aabb'))
     elif impl == 'warp':
diff --git a/mjx/mujoco/mjx/_src/types.py b/mjx/mujoco/mjx/_src/types.py
index a15214ec..d1a25168 100644
--- a/mjx/mujoco/mjx/_src/types.py
+++ b/mjx/mujoco/mjx/_src/types.py
@@ -497,7 +497,6 @@ class OptionC(PyTreeNode):
   disableactuator: int
   sdf_initpoints: int
   has_fluid_params: bool
-  apirate: jax.Array
   noslip_tolerance: jax.Array
   ccd_tolerance: jax.Array
   noslip_iterations: int
diff --git a/python/mujoco/introspect/structs.py b/python/mujoco/introspect/structs.py
index 5d187cf3..c866e7aa 100644
--- a/python/mujoco/introspect/structs.py
+++ b/python/mujoco/introspect/structs.py
@@ -123,11 +123,6 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  type=ValueType(name='mjtNum'),
                  doc='timestep',
              ),
-             StructFieldDecl(
-                 name='apirate',
-                 type=ValueType(name='mjtNum'),
-                 doc='update rate for remote API (Hz)',
-             ),
              StructFieldDecl(
                  name='impratio',
                  type=ValueType(name='mjtNum'),
diff --git a/simulate/simulate.cc b/simulate/simulate.cc
index 3fb21976..d6a5f80e 100644
--- a/simulate/simulate.cc
+++ b/simulate/simulate.cc
@@ -707,7 +707,6 @@ void MakePhysicsSection(mj::Simulate* sim) {
     {mjITEM_EDITNUM,   "Noslip Tol",    2, &(opt->noslip_tolerance),  "1 0 1"},
     {mjITEM_EDITINT,   "CCD Iter",      2, &(opt->ccd_iterations),    "1 0 1000"},
     {mjITEM_EDITNUM,   "CCD Tol",       2, &(opt->ccd_tolerance),     "1 0 1"},
-    {mjITEM_EDITNUM,   "API Rate",      2, &(opt->apirate),           "1 0 1000"},
     {mjITEM_EDITINT,   "SDF Iter",      2, &(opt->sdf_iterations),    "1 1 20"},
     {mjITEM_EDITINT,   "SDF Init",      2, &(opt->sdf_initpoints),    "1 1 100"},
     {mjITEM_SEPARATOR, "Physical Parameters", mjPRESERVE},
diff --git a/src/engine/engine_init.c b/src/engine/engine_init.c
index 80c3de69..6ca8a7b0 100644
--- a/src/engine/engine_init.c
+++ b/src/engine/engine_init.c
@@ -54,7 +54,6 @@ void mj_defaultOption(mjOption* opt) {
 
   // timing parameters
   opt->timestep           = 0.002;
-  opt->apirate            = 100;
 
   // solver parameters
   opt->impratio           = 1;
diff --git a/src/experimental/studio/app.cc b/src/experimental/studio/app.cc
index 6d6529c2..2a00e300 100644
--- a/src/experimental/studio/app.cc
+++ b/src/experimental/studio/app.cc
@@ -1364,7 +1364,6 @@ void App::PhysicsGui() {
     ImGui_Input("Noslip Tol", &opt.noslip_tolerance, {0, 1, 0.01, 0.1, w});
     ImGui_Input("CCD Iter", &opt.ccd_iterations, {0, 1000, 1, 100, w});
     ImGui_Input("CCD Tol", &opt.ccd_tolerance, {0, 1, 0.01, 0.1, w});
-    ImGui_Input("API Rate", &opt.apirate, {0, 1000, 1, 100, w});
     ImGui_Input("SDF Iter", &opt.sdf_iterations, {1, 20, 1, 10, w});
     ImGui_Input("SDF Init", &opt.sdf_initpoints, {1, 100, 1, 10, w});
     ImGui::TreePop();
diff --git a/src/experimental/usd/mjcPhysics/generatedSchema.usda b/src/experimental/usd/mjcPhysics/generatedSchema.usda
index 5d8aa4ad..1c246fba 100644
--- a/src/experimental/usd/mjcPhysics/generatedSchema.usda
+++ b/src/experimental/usd/mjcPhysics/generatedSchema.usda
@@ -170,11 +170,6 @@ class "MjcSceneAPI" (
         displayName = "Actuator Group Disable"
         doc = "List of actuator groups to disable."
     )
-    uniform double mjc:option:apirate = 100 (
-        displayName = "ApiRate"
-        doc = """Determines the rate (in Hz) at which an external API allows
-        the update function to be executed."""
-    )
     uniform int mjc:option:ccd_iterations = 35 (
         displayName = "CCD Iterations"
         doc = "Maximum number of iterations of the algorithm used for convex collisions."
diff --git a/src/experimental/usd/mjcPhysics/sceneAPI.cpp b/src/experimental/usd/mjcPhysics/sceneAPI.cpp
index 31e6e1ed..6396c858 100644
--- a/src/experimental/usd/mjcPhysics/sceneAPI.cpp
+++ b/src/experimental/usd/mjcPhysics/sceneAPI.cpp
@@ -85,17 +85,6 @@ UsdAttribute MjcPhysicsSceneAPI::CreateTimestepAttr(VtValue const& defaultValue,
       /* custom = */ false, SdfVariabilityUniform, defaultValue, writeSparsely);
 }
 
-UsdAttribute MjcPhysicsSceneAPI::GetApiRateAttr() const {
-  return GetPrim().GetAttribute(MjcPhysicsTokens->mjcOptionApirate);
-}
-
-UsdAttribute MjcPhysicsSceneAPI::CreateApiRateAttr(VtValue const& defaultValue,
-                                                   bool writeSparsely) const {
-  return UsdSchemaBase::_CreateAttr(
-      MjcPhysicsTokens->mjcOptionApirate, SdfValueTypeNames->Double,
-      /* custom = */ false, SdfVariabilityUniform, defaultValue, writeSparsely);
-}
-
 UsdAttribute MjcPhysicsSceneAPI::GetImpRatioAttr() const {
   return GetPrim().GetAttribute(MjcPhysicsTokens->mjcOptionImpratio);
 }
@@ -798,7 +787,6 @@ const TfTokenVector& MjcPhysicsSceneAPI::GetSchemaAttributeNames(
     bool includeInherited) {
   static TfTokenVector localNames = {
       MjcPhysicsTokens->mjcOptionTimestep,
-      MjcPhysicsTokens->mjcOptionApirate,
       MjcPhysicsTokens->mjcOptionImpratio,
       MjcPhysicsTokens->mjcOptionWind,
       MjcPhysicsTokens->mjcOptionMagnetic,
diff --git a/src/experimental/usd/mjcPhysics/schema.usda b/src/experimental/usd/mjcPhysics/schema.usda
index dfff4862..ccece96a 100644
--- a/src/experimental/usd/mjcPhysics/schema.usda
+++ b/src/experimental/usd/mjcPhysics/schema.usda
@@ -111,15 +111,6 @@ class "MjcSceneAPI"
         doc = """Controls the timestep in seconds used by MuJoCo."""
     )
 
-    uniform double mjc:option:apirate = 100 (
-        customData = {
-            string apiName = "ApiRate"
-        }
-        displayName = "ApiRate"
-        doc = """Determines the rate (in Hz) at which an external API allows
-        the update function to be executed."""
-    )
-
     uniform double mjc:option:impratio = 1.0 (
         customData = {
             string apiName = "ImpRatio"
diff --git a/src/experimental/usd/mjcPhysics/tokens.cpp b/src/experimental/usd/mjcPhysics/tokens.cpp
index 73fce427..61610159 100644
--- a/src/experimental/usd/mjcPhysics/tokens.cpp
+++ b/src/experimental/usd/mjcPhysics/tokens.cpp
@@ -118,7 +118,6 @@ MjcPhysicsTokensType::MjcPhysicsTokensType()
       mjcMquat("mjc:mquat", TfToken::Immortal),
       mjcOptionActuatorgroupdisable("mjc:option:actuatorgroupdisable",
                                     TfToken::Immortal),
-      mjcOptionApirate("mjc:option:apirate", TfToken::Immortal),
       mjcOptionCcd_iterations("mjc:option:ccd_iterations", TfToken::Immortal),
       mjcOptionCcd_tolerance("mjc:option:ccd_tolerance", TfToken::Immortal),
       mjcOptionCone("mjc:option:cone", TfToken::Immortal),
@@ -281,7 +280,6 @@ MjcPhysicsTokensType::MjcPhysicsTokensType()
                  mjcMpos,
                  mjcMquat,
                  mjcOptionActuatorgroupdisable,
-                 mjcOptionApirate,
                  mjcOptionCcd_iterations,
                  mjcOptionCcd_tolerance,
                  mjcOptionCone,
diff --git a/src/experimental/usd/plugins/mjcf/mujoco_to_usd.cc b/src/experimental/usd/plugins/mjcf/mujoco_to_usd.cc
index 4fdb57fe..4a444914 100644
--- a/src/experimental/usd/plugins/mjcf/mujoco_to_usd.cc
+++ b/src/experimental/usd/plugins/mjcf/mujoco_to_usd.cc
@@ -500,7 +500,6 @@ class ModelWriter {
              spec_->option.noslip_tolerance},
             {MjcPhysicsTokens->mjcOptionCcd_tolerance,
              spec_->option.ccd_tolerance},
-            {MjcPhysicsTokens->mjcOptionApirate, spec_->option.apirate},
             {MjcPhysicsTokens->mjcOptionImpratio, spec_->option.impratio},
             {MjcPhysicsTokens->mjcOptionDensity, spec_->option.density},
             {MjcPhysicsTokens->mjcOptionViscosity, spec_->option.viscosity},
diff --git a/src/experimental/usd/usd_to_mjspec.cc b/src/experimental/usd/usd_to_mjspec.cc
index d348ba87..b3ca5d26 100644
--- a/src/experimental/usd/usd_to_mjspec.cc
+++ b/src/experimental/usd/usd_to_mjspec.cc
@@ -445,10 +445,6 @@ void ParseUsdPhysicsScene(mjSpec* spec,
   mjc_physics_scene.GetTimestepAttr().Get(&timestep);
   spec->option.timestep = timestep;
 
-  double apirate;
-  mjc_physics_scene.GetApiRateAttr().Get(&apirate);
-  spec->option.apirate = apirate;
-
   double impratio;
   mjc_physics_scene.GetImpRatioAttr().Get(&impratio);
   spec->option.impratio = impratio;
diff --git a/src/xml/xml_native_reader.cc b/src/xml/xml_native_reader.cc
index 4a604173..9bc462cb 100644
--- a/src/xml/xml_native_reader.cc
+++ b/src/xml/xml_native_reader.cc
@@ -110,8 +110,8 @@ const char* MJCF[nMJCF][mjXATTRNUM] = {
             "inttotal", "interval", "tolrange"},
     {">"},
 
-    {"option", "*", "27",
-        "timestep", "apirate", "impratio", "tolerance", "ls_tolerance", "noslip_tolerance",
+    {"option", "*", "26",
+        "timestep", "impratio", "tolerance", "ls_tolerance", "noslip_tolerance",
         "ccd_tolerance", "gravity", "wind", "magnetic", "density", "viscosity",
         "o_margin", "o_solref", "o_solimp", "o_friction",
         "integrator", "cone", "jacobian",
@@ -1130,7 +1130,6 @@ void mjXReader::Option(XMLElement* section, mjOption* opt) {
 
   // read options
   ReadAttr(section, "timestep", 1, &opt->timestep, text);
-  ReadAttr(section, "apirate", 1, &opt->apirate, text);
   ReadAttr(section, "impratio", 1, &opt->impratio, text);
   ReadAttr(section, "tolerance", 1, &opt->tolerance, text);
   ReadAttr(section, "ls_tolerance", 1, &opt->ls_tolerance, text);
diff --git a/src/xml/xml_native_writer.cc b/src/xml/xml_native_writer.cc
index ea55f5c2..0fb2a47c 100644
--- a/src/xml/xml_native_writer.cc
+++ b/src/xml/xml_native_writer.cc
@@ -990,7 +990,6 @@ void mjXWriter::Option(XMLElement* root) {
 
   // option
   WriteAttr(section, "timestep", 1, &model->option.timestep, &opt.timestep);
-  WriteAttr(section, "apirate", 1, &model->option.apirate, &opt.apirate);
   WriteAttr(section, "impratio", 1, &model->option.impratio, &opt.impratio);
   WriteAttr(section, "tolerance", 1, &model->option.tolerance, &opt.tolerance);
   WriteAttr(section, "ls_tolerance", 1, &model->option.ls_tolerance, &opt.ls_tolerance);
diff --git a/test/experimental/usd/mjcPhysics/mjc_physics_scene_test.cc b/test/experimental/usd/mjcPhysics/mjc_physics_scene_test.cc
index dc11a10d..30cb4d70 100644
--- a/test/experimental/usd/mjcPhysics/mjc_physics_scene_test.cc
+++ b/test/experimental/usd/mjcPhysics/mjc_physics_scene_test.cc
@@ -104,7 +104,6 @@ TEST_F(MjcPhysicsSceneTest, TestDefaults) {
   // If this test is failing due to an update of defaults in Mujoco you need to
   // update mjcPhysics/schema.usda.
   EXPECT_REAL_USD_FALLBACK_EQ_MODEL_DEFAULT(Timestep, timestep);
-  EXPECT_REAL_USD_FALLBACK_EQ_MODEL_DEFAULT(ApiRate, apirate);
   EXPECT_REAL_USD_FALLBACK_EQ_MODEL_DEFAULT(ImpRatio, impratio);
 
   EXPECT_VEC3_USD_FALLBACK_EQ_MODEL_DEFAULT(Wind, wind);
diff --git a/test/experimental/usd/plugins/mjcf/mjcf_file_format_test.cc b/test/experimental/usd/plugins/mjcf/mjcf_file_format_test.cc
index 30385b42..1ada4fa5 100644
--- a/test/experimental/usd/plugins/mjcf/mjcf_file_format_test.cc
+++ b/test/experimental/usd/plugins/mjcf/mjcf_file_format_test.cc
@@ -724,19 +724,6 @@ TEST_F(MjcfSdfFileFormatPluginTest, TestPhysicsScenePrimWind) {
       pxr::GfVec3d(1, 2, 3));
 }
 
-TEST_F(MjcfSdfFileFormatPluginTest, TestPhysicsScenePrimApirate) {
-  auto stage = OpenStage(R"(
-    <mujoco model="test">
-      <option apirate="1.2"> </option>
-    </mujoco>
-  )");
-
-  ExpectAttributeEqual(
-      stage,
-      kPhysicsScenePrimPath.AppendProperty(MjcPhysicsTokens->mjcOptionApirate),
-      1.2);
-}
-
 TEST_F(MjcfSdfFileFormatPluginTest, TestPhysicsScenePrimImpratio) {
   auto stage = OpenStage(R"(
     <mujoco model="test">
diff --git a/unity/Runtime/Bindings/MjBindings.cs b/unity/Runtime/Bindings/MjBindings.cs
index f3dc8f43..8ad78169 100644
--- a/unity/Runtime/Bindings/MjBindings.cs
+++ b/unity/Runtime/Bindings/MjBindings.cs
@@ -5089,7 +5089,6 @@ public unsafe struct _mjVFS
 [StructLayout(LayoutKind.Sequential)]
 public unsafe struct mjOption_ {
   public double timestep;
-  public double apirate;
   public double impratio;
   public double tolerance;
   public double ls_tolerance;
diff --git a/unity/Runtime/Components/MjGlobalSettings.cs b/unity/Runtime/Components/MjGlobalSettings.cs
index d41cefe5..11e41306 100644
--- a/unity/Runtime/Components/MjGlobalSettings.cs
+++ b/unity/Runtime/Components/MjGlobalSettings.cs
@@ -156,7 +156,6 @@ public struct MjSizeStruct {
 public struct MjOptionStruct {
 
   // "timestep" and "gravity" come from global settings.
-  // "apirate" is only relevant to HAPTIX.
   [Tooltip("Ratio of frictional-to-normal constraint impedance.")]
   public float ImpRatio;
   [Tooltip("Global magnetic flux used by magnetometer sensors.")]