diff --git a/src/opsinputs/CxWriter.cc b/src/opsinputs/CxWriter.cc
index 2018f867..1ca7058a 100644
--- a/src/opsinputs/CxWriter.cc
+++ b/src/opsinputs/CxWriter.cc
@@ -13,7 +13,6 @@
 #include "ioda/ObsDataVector.h"
 #include "ioda/ObsSpace.h"
 #include "ioda/ObsVector.h"
-#include "oops/base/Variables.h"
 #include "oops/util/Logger.h"
 #include "opsinputs/CxWriterParameters.h"
 #include "opsinputs/LocalEnvironment.h"
@@ -93,7 +92,7 @@ void CxWriter::postFilter(const ufo::GeoVaLs & gv,
     ufo::Variables filtervars;
     for (const ufo::Variable &var : parameters_.variables_for_qc.value().get())
       filtervars += var;
-    ioda::ObsDataVector<int> flags(obsdb_, filtervars.toOopsVariables());
+    ioda::ObsDataVector<int> flags(obsdb_, filtervars.toOopsObsVariables());
     for (int ivar = 0; ivar < flags.nvars(); ivar++) {
       const std::string varname = flags.varnames()[ivar];
       flags[varname] = flags_->operator[](varname);
diff --git a/src/opsinputs/CxWriter.h b/src/opsinputs/CxWriter.h
index b9891821..c0ece6da 100644
--- a/src/opsinputs/CxWriter.h
+++ b/src/opsinputs/CxWriter.h
@@ -11,6 +11,7 @@
 #include <string>
 
 #include "ioda/ObsDataVector.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "oops/interface/ObsFilterBase.h"
 #include "oops/util/ObjectCounter.h"
@@ -64,7 +65,7 @@ class CxWriter : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
   void checkFilterData(const oops::FilterStage filterStage) override {}
 
   oops::Variables requiredVars() const override {return geovars_;}
-  oops::Variables requiredHdiagnostics() const override {return extradiagvars_;}
+  oops::ObsVariables requiredHdiagnostics() const override {return extradiagvars_;}
 
  private:
   void print(std::ostream &) const override;
@@ -77,7 +78,7 @@ class CxWriter : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
 
   ioda::ObsSpace & obsdb_;
   oops::Variables geovars_;
-  oops::Variables extradiagvars_;
+  oops::ObsVariables extradiagvars_;
   std::shared_ptr<ioda::ObsDataVector<int>> flags_;
   std::shared_ptr<ioda::ObsDataVector<float>> obsErrors_;
 
diff --git a/src/opsinputs/CxWriter.interface.F90 b/src/opsinputs/CxWriter.interface.F90
index f5cf7e73..7728fb0d 100644
--- a/src/opsinputs/CxWriter.interface.F90
+++ b/src/opsinputs/CxWriter.interface.F90
@@ -10,6 +10,7 @@ module opsinputs_cxwriter_mod_c
   c_bool,                              &
   c_int,                               &
   c_ptr
+use obs_variables_mod, only: obs_variables
 use oops_variables_mod, only: oops_variables
 use opsinputs_cxwriter_mod, only:  &
   opsinputs_cxwriter,              &
@@ -112,13 +113,13 @@ subroutine opsinputs_cxwriter_post_c(c_self, c_obspace, c_geovals, c_flags, &
 
 type(opsinputs_cxwriter), pointer :: self
 type(ufo_geovals), pointer :: geovals
-type(oops_variables) :: f_varnames
+type(obs_variables) :: f_varnames
 
 call opsinputs_cxwriter_registry%get(c_self, self)
 call ufo_geovals_registry%get(c_geovals, geovals)
 
 ! Obtain simulated variable names.
-f_varnames = oops_variables(c_varnames)
+f_varnames = obs_variables(c_varnames)
 
 call opsinputs_cxwriter_post(self, c_obspace, geovals, c_flags, &
                              f_varnames, c_hofx)
diff --git a/src/opsinputs/CxWriter.interface.h b/src/opsinputs/CxWriter.interface.h
index 96d4cfe9..d8fe3d4f 100644
--- a/src/opsinputs/CxWriter.interface.h
+++ b/src/opsinputs/CxWriter.interface.h
@@ -7,6 +7,7 @@
 #define OPSINPUTS_CXWRITER_INTERFACE_H_
 
 #include "ioda/ObsSpace.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "ufo/Fortran.h"
 
@@ -37,7 +38,7 @@ extern "C" {
                                    const ufo::F90goms &,
                                    const ioda::ObsDataVector<int> &flags,
                                    const int &nvars, const int &nlocs,
-                                   const oops::Variables &varnames, const double *hofx);
+                                   const oops::ObsVariables &varnames, const double *hofx);
 }  // extern C
 
 }  // namespace opsinputs
diff --git a/src/opsinputs/VarObsWriter.cc b/src/opsinputs/VarObsWriter.cc
index 69e350e2..d254f145 100644
--- a/src/opsinputs/VarObsWriter.cc
+++ b/src/opsinputs/VarObsWriter.cc
@@ -15,7 +15,6 @@
 #include "ioda/ObsDataVector.h"
 #include "ioda/ObsSpace.h"
 #include "ioda/ObsVector.h"
-#include "oops/base/Variables.h"
 #include "oops/mpi/mpi.h"
 #include "oops/util/IntSetParser.h"
 #include "oops/util/Logger.h"
@@ -121,7 +120,7 @@ void VarObsWriter::postFilter(const ufo::GeoVaLs & gv,
     ufo::Variables filtervars;
     for (const ufo::Variable &var : parameters_.variables_for_qc.value().get())
       filtervars += var;
-    ioda::ObsDataVector<int> flags(obsdb_, filtervars.toOopsVariables());
+    ioda::ObsDataVector<int> flags(obsdb_, filtervars.toOopsObsVariables());
     for (int ivar = 0; ivar < flags.nvars(); ivar++) {
       std::string varname = flags.varnames()[ivar];
       flags[varname] = flags_->operator[](varname);
diff --git a/src/opsinputs/VarObsWriter.h b/src/opsinputs/VarObsWriter.h
index 585dbb42..6c4d214b 100644
--- a/src/opsinputs/VarObsWriter.h
+++ b/src/opsinputs/VarObsWriter.h
@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "ioda/ObsDataVector.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "oops/interface/ObsFilterBase.h"
 #include "oops/util/ObjectCounter.h"
@@ -73,7 +74,7 @@ class VarObsWriter : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
   void checkFilterData(const oops::FilterStage filterStage) override {}
 
   oops::Variables requiredVars() const override {return geovars_;}
-  oops::Variables requiredHdiagnostics() const override {return extradiagvars_;}
+  oops::ObsVariables requiredHdiagnostics() const override {return extradiagvars_;}
 
  private:
   void print(std::ostream &) const override;
@@ -86,7 +87,7 @@ class VarObsWriter : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
 
   ioda::ObsSpace & obsdb_;
   oops::Variables geovars_;
-  oops::Variables extradiagvars_;
+  oops::ObsVariables extradiagvars_;
   std::shared_ptr<ioda::ObsDataVector<int>> flags_;
   std::shared_ptr<ioda::ObsDataVector<float>> obsErrors_;
   std::vector<int> varchannels_;
diff --git a/src/opsinputs/VarObsWriter.interface.F90 b/src/opsinputs/VarObsWriter.interface.F90
index b4e920e2..eb4bd6ff 100644
--- a/src/opsinputs/VarObsWriter.interface.F90
+++ b/src/opsinputs/VarObsWriter.interface.F90
@@ -44,6 +44,7 @@ function opsinputs_varobswriter_create_c(c_self, c_conf, c_comm_is_valid, c_comm
                                          c_varlist, c_varlist_diags) &
   bind(c,name='opsinputs_varobswriter_create_f90')
 use oops_variables_mod
+use obs_variables_mod
 implicit none
 integer(c_int), intent(inout)  :: c_self
 type(c_ptr), value, intent(in) :: c_conf
@@ -61,14 +62,14 @@ function opsinputs_varobswriter_create_c(c_self, c_conf, c_comm_is_valid, c_comm
 type(fckit_configuration) :: f_conf
 integer(gc_int_kind) :: f_comm
 type(oops_variables) :: f_varlist
-type(oops_variables) :: f_varlist_diags
+type(obs_variables)  :: f_varlist_diags
 
 call opsinputs_varobswriter_registry%setup(c_self, self)
 
 f_conf = fckit_configuration(c_conf)
 f_comm = c_comm
 f_varlist = oops_variables(c_varlist)
-f_varlist_diags = oops_variables(c_varlist_diags)
+f_varlist_diags = obs_variables(c_varlist_diags)
 if (opsinputs_varobswriter_create(self, f_conf, c_comm_is_valid, f_comm, c_channels, &
                                   f_varlist, f_varlist_diags)) then
   opsinputs_varobswriter_create_c = 1
diff --git a/src/opsinputs/VarObsWriter.interface.h b/src/opsinputs/VarObsWriter.interface.h
index a3103e4d..73281395 100644
--- a/src/opsinputs/VarObsWriter.interface.h
+++ b/src/opsinputs/VarObsWriter.interface.h
@@ -9,6 +9,7 @@
 #include <mpi.h>
 
 #include "ioda/ObsSpace.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "ufo/Fortran.h"
 
@@ -34,7 +35,7 @@ extern "C" {
                                         const MPI_Fint &comm,
                                         const int &nchannels,
                                         const int *channels,
-                                        oops::Variables &, oops::Variables &);
+                                        oops::Variables &, oops::ObsVariables &);
   void opsinputs_varobswriter_delete_f90(F90check &);
   void opsinputs_varobswriter_prior_f90(const F90check &, const ioda::ObsSpace &,
                                        const ufo::F90goms &);
diff --git a/src/opsinputs/opsinputs_cxwriter_mod.F90 b/src/opsinputs/opsinputs_cxwriter_mod.F90
index 6767bbbe..67738a66 100644
--- a/src/opsinputs/opsinputs_cxwriter_mod.F90
+++ b/src/opsinputs/opsinputs_cxwriter_mod.F90
@@ -22,6 +22,7 @@ module opsinputs_cxwriter_mod
 use obsspace_mod, only: &
     obsspace_get_db,    &
     obsspace_get_nlocs
+use obs_variables_mod, only: obs_variables
 use oops_variables_mod, only: oops_variables
 use opsinputs_cxfields_mod
 use opsinputs_fill_mod, only:                 &
@@ -173,7 +174,7 @@ module opsinputs_cxwriter_mod
 
   type(ufo_geovals), pointer             :: GeoVals
   type(opsinputs_jeditoopslayoutmapping) :: JediToOpsLayoutMapping
-  type(oops_variables)                   :: varnames
+  type(obs_variables)                    :: varnames
   real(c_double), pointer                :: hofx(:, :)
 end type opsinputs_cxwriter
 
@@ -501,7 +502,7 @@ subroutine opsinputs_cxwriter_post(self, ObsSpace, GeoVals, Flags, varnames, hof
 type(c_ptr), value, intent(in)          :: ObsSpace
 type(ufo_geovals), intent(in), pointer  :: GeoVals
 type(c_ptr), value, intent(in)          :: Flags
-type(oops_variables), intent(in)        :: varnames
+type(obs_variables), intent(in)         :: varnames
 real(c_double), intent(in), target      :: hofx(:, :)
 
 ! Local declarations:
diff --git a/src/opsinputs/opsinputs_fill_mod.F90 b/src/opsinputs/opsinputs_fill_mod.F90
index 9f544501..e016154e 100644
--- a/src/opsinputs/opsinputs_fill_mod.F90
+++ b/src/opsinputs/opsinputs_fill_mod.F90
@@ -17,6 +17,7 @@ module opsinputs_fill_mod
 use obsspace_mod, only: &
     obsspace_has,         &
     obsspace_get_db
+use obs_variables_mod, only: obs_variables
 use oops_variables_mod, only: oops_variables
 use ufo_geovals_mod, only: &
     ufo_geoval,            &
@@ -1487,7 +1488,7 @@ subroutine opsinputs_fill_fillreal2dfromgeovalorhofx( &
 character(len=*), intent(in)                       :: JediVarName
 type(opsinputs_jeditoopslayoutmapping), intent(in) :: JediToOpsLayoutMapping
 real(c_double), intent(in)                         :: hofx(:, :)
-type(oops_variables), intent(in)                   :: varnames
+type(obs_variables), intent(in)                    :: varnames
 character(len=*), intent(in), optional             :: JediObsName
 logical, intent(in), optional                      :: WriteHofXIntoCX
 
diff --git a/src/opsinputs/opsinputs_obsdatavector_f.cc b/src/opsinputs/opsinputs_obsdatavector_f.cc
index 0be6a677..b918bc98 100644
--- a/src/opsinputs/opsinputs_obsdatavector_f.cc
+++ b/src/opsinputs/opsinputs_obsdatavector_f.cc
@@ -24,7 +24,7 @@ int opsinputs_obsdatavector_nlocs_f(const ioda::ObsDataVector<T> &vec) {
 }
 
 template <typename T>
-const oops::Variables * opsinputs_obsdatavector_varnames_f(
+const oops::ObsVariables * opsinputs_obsdatavector_varnames_f(
     const ioda::ObsDataVector<T> &vec) {
   return &vec.varnames();
 }
@@ -50,7 +50,7 @@ int opsinputs_obsdatavector_int_nlocs_f(const ioda::ObsDataVector<int> &vec) {
   return opsinputs_obsdatavector_nlocs_f(vec);
 }
 
-const oops::Variables * opsinputs_obsdatavector_int_varnames_f(
+const oops::ObsVariables * opsinputs_obsdatavector_int_varnames_f(
     const ioda::ObsDataVector<int> &vec) {
   return opsinputs_obsdatavector_varnames_f(vec);
 }
@@ -70,7 +70,7 @@ int opsinputs_obsdatavector_float_nlocs_f(const ioda::ObsDataVector<float> &vec)
   return opsinputs_obsdatavector_nlocs_f(vec);
 }
 
-const oops::Variables * opsinputs_obsdatavector_float_varnames_f(
+const oops::ObsVariables * opsinputs_obsdatavector_float_varnames_f(
     const ioda::ObsDataVector<float> &vec) {
   return opsinputs_obsdatavector_varnames_f(vec);
 }
diff --git a/src/opsinputs/opsinputs_obsdatavector_f.h b/src/opsinputs/opsinputs_obsdatavector_f.h
index 408c0e50..460480ac 100644
--- a/src/opsinputs/opsinputs_obsdatavector_f.h
+++ b/src/opsinputs/opsinputs_obsdatavector_f.h
@@ -15,6 +15,7 @@ namespace ioda {
 }  // namespace ioda
 
 namespace oops {
+  class ObsVariables;
   class Variables;
 }  // namespace oops
 
@@ -22,7 +23,7 @@ namespace opsinputs {
 
 extern "C" {
   int opsinputs_obsdatavector_int_nlocs_f(const ioda::ObsDataVector<int> &vec);
-  const oops::Variables * opsinputs_obsdatavector_int_varnames_f(
+  const oops::ObsVariables * opsinputs_obsdatavector_int_varnames_f(
       const ioda::ObsDataVector<int> &vec);
   bool opsinputs_obsdatavector_int_has_f(const ioda::ObsDataVector<int> &vec,
                                         const char *variable);
@@ -31,7 +32,7 @@ extern "C" {
                                         const size_t &length, int* data);
 
   int opsinputs_obsdatavector_float_nlocs_f(const ioda::ObsDataVector<float> &vec);
-  const oops::Variables * opsinputs_obsdatavector_float_varnames_f(
+  const oops::ObsVariables * opsinputs_obsdatavector_float_varnames_f(
       const ioda::ObsDataVector<float> &vec);
   bool opsinputs_obsdatavector_float_has_f(const ioda::ObsDataVector<float> &vec,
                                           const char *variable);
diff --git a/src/opsinputs/opsinputs_varobswriter_mod.F90 b/src/opsinputs/opsinputs_varobswriter_mod.F90
index fd5b6593..5856a791 100644
--- a/src/opsinputs/opsinputs_varobswriter_mod.F90
+++ b/src/opsinputs/opsinputs_varobswriter_mod.F90
@@ -25,6 +25,7 @@ module opsinputs_varobswriter_mod
     obsspace_get_gnlocs, &
     obsspace_get_nlocs,  &
     obsspace_has
+use obs_variables_mod, only: obs_variables
 use oops_variables_mod, only: oops_variables
 use opsinputs_fill_mod, only: &
     opsinputs_fill_fillcoord2d, &
@@ -219,7 +220,7 @@ function opsinputs_varobswriter_create(self, f_conf, comm_is_valid, comm, channe
 integer(gc_int_kind), intent(in)           :: comm
 integer(c_int), intent(in)                 :: channels(:)
 type(oops_variables), intent(inout)        :: geovars  ! GeoVaLs required by the VarObsWriter.
-type(oops_variables), intent(inout)        :: diagvars ! HofXDiags required by the VarObsWriter.
+type(obs_variables), intent(inout)         :: diagvars ! HofXDiags required by the VarObsWriter.
 logical                                    :: opsinputs_varobswriter_create
 
 ! Local declarations:
@@ -622,7 +623,7 @@ subroutine opsinputs_varobswriter_addrequireddiagvars(self, diagvars)
 
 ! Subroutine arguments:
 type(opsinputs_varobswriter), intent(in) :: self
-type(oops_variables), intent(inout)      :: diagvars
+type(obs_variables), intent(inout)       :: diagvars
 
 ! Local declarations:
 integer(integer64)                       :: VarFields(ActualMaxVarfield)
diff --git a/test/opsinputs/CxChecker.h b/test/opsinputs/CxChecker.h
index 1355c08b..53bf8ca9 100644
--- a/test/opsinputs/CxChecker.h
+++ b/test/opsinputs/CxChecker.h
@@ -14,6 +14,7 @@
 
 #include "../opsinputs/CxCheckerParameters.h"
 #include "ioda/ObsDataVector.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "oops/interface/ObsFilterBase.h"
 #include "oops/util/ObjectCounter.h"
@@ -70,7 +71,7 @@ class CxChecker : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
   void checkFilterData(const oops::FilterStage filterStage) override {}
 
   oops::Variables requiredVars() const override {return geovars_;}
-  oops::Variables requiredHdiagnostics() const override {return extradiagvars_;}
+  oops::ObsVariables requiredHdiagnostics() const override {return extradiagvars_;}
 
  private:
   struct PrintCxFileOutput;
@@ -94,7 +95,7 @@ class CxChecker : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
 
   ioda::ObsSpace & obsdb_;
   oops::Variables geovars_;
-  oops::Variables extradiagvars_;
+  oops::ObsVariables extradiagvars_;
   std::shared_ptr<ioda::ObsDataVector<int>> flags_;
   std::shared_ptr<ioda::ObsDataVector<float>> obsErrors_;
 
diff --git a/test/opsinputs/ResetFlagsToPass.cc b/test/opsinputs/ResetFlagsToPass.cc
index 87a2c295..e4da069c 100644
--- a/test/opsinputs/ResetFlagsToPass.cc
+++ b/test/opsinputs/ResetFlagsToPass.cc
@@ -9,7 +9,6 @@
 
 #include "ioda/ObsDataVector.h"
 #include "ioda/ObsSpace.h"
-#include "oops/base/Variables.h"
 #include "oops/util/IntSetParser.h"  // for contains()
 #include "oops/util/Logger.h"
 #include "ufo/filters/QCflags.h"
diff --git a/test/opsinputs/ResetFlagsToPass.h b/test/opsinputs/ResetFlagsToPass.h
index 715e0fac..9fae44c7 100644
--- a/test/opsinputs/ResetFlagsToPass.h
+++ b/test/opsinputs/ResetFlagsToPass.h
@@ -13,6 +13,7 @@
 
 #include "../opsinputs/ResetFlagsToPassParameters.h"
 #include "ioda/ObsDataVector.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "oops/interface/ObsFilterBase.h"
 #include "oops/util/ObjectCounter.h"
@@ -62,14 +63,14 @@ class ResetFlagsToPass : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
   void checkFilterData(const oops::FilterStage filterStage) override {}
 
   oops::Variables requiredVars() const override {return geovars_;}
-  oops::Variables requiredHdiagnostics() const override {return extradiagvars_;}
+  oops::ObsVariables requiredHdiagnostics() const override {return extradiagvars_;}
 
  private:
   void print(std::ostream &) const override;
 
   ioda::ObsSpace & obsdb_;
   oops::Variables geovars_;
-  oops::Variables extradiagvars_;
+  oops::ObsVariables extradiagvars_;
   std::shared_ptr<ioda::ObsDataVector<int>> flags_;
 
   ResetFlagsToPassParameters parameters_;
diff --git a/test/opsinputs/VarObsChecker.cc b/test/opsinputs/VarObsChecker.cc
index ce4a4a08..a0820c4a 100644
--- a/test/opsinputs/VarObsChecker.cc
+++ b/test/opsinputs/VarObsChecker.cc
@@ -19,7 +19,6 @@
 
 #include "ioda/ObsDataVector.h"
 #include "ioda/ObsSpace.h"
-#include "oops/base/Variables.h"
 #include "oops/mpi/mpi.h"
 #include "oops/util/Logger.h"
 
diff --git a/test/opsinputs/VarObsChecker.h b/test/opsinputs/VarObsChecker.h
index 82a55d50..1f2f64c4 100644
--- a/test/opsinputs/VarObsChecker.h
+++ b/test/opsinputs/VarObsChecker.h
@@ -13,6 +13,7 @@
 
 #include "../opsinputs/VarObsCheckerParameters.h"
 #include "ioda/ObsDataVector.h"
+#include "oops/base/ObsVariables.h"
 #include "oops/base/Variables.h"
 #include "oops/interface/ObsFilterBase.h"
 #include "oops/util/ObjectCounter.h"
@@ -69,7 +70,7 @@ class VarObsChecker : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
   void checkFilterData(const oops::FilterStage filterStage) override {}
 
   oops::Variables requiredVars() const override {return geovars_;}
-  oops::Variables requiredHdiagnostics() const override {return extradiagvars_;}
+  oops::ObsVariables requiredHdiagnostics() const override {return extradiagvars_;}
 
  private:
   struct PrintVarObsOutput;
@@ -87,7 +88,7 @@ class VarObsChecker : public oops::interface::ObsFilterBase<ufo::ObsTraits>,
 
   ioda::ObsSpace & obsdb_;
   oops::Variables geovars_;
-  oops::Variables extradiagvars_;
+  oops::ObsVariables extradiagvars_;
   std::shared_ptr<ioda::ObsDataVector<int>> flags_;
   std::shared_ptr<ioda::ObsDataVector<float>> obsErrors_;