diff --git a/lib/xos-genx/xosgenx/generator.py b/lib/xos-genx/xosgenx/generator.py
index d1dc99a..278a309 100644
--- a/lib/xos-genx/xosgenx/generator.py
+++ b/lib/xos-genx/xosgenx/generator.py
@@ -174,20 +174,6 @@
             print("Saved: %s" % file_name)
 
     @staticmethod
-    def _write_file_per_model(rendered, dir, suffix, quiet):
-        for m in rendered:
-            file_name = "%s/%s%s" % (dir, m.lower(), suffix)
-            if not rendered[m]:
-                if not quiet:
-                    print("Not saving %s as it is empty" % file_name)
-            else:
-                file = open(file_name, "w")
-                file.write(rendered[m])
-                file.close()
-                if not quiet:
-                    print("Saved: %s" % file_name)
-
-    @staticmethod
     def _write_split_target(rendered, dir, quiet):
 
         lines = rendered.splitlines()
@@ -348,16 +334,17 @@
         template = os_template_env.get_template(template_name)
 
         if args.output is not None and args.write_to_file == "model":
+            # Handle the case where each model is written to a separate python file.
             rendered = {}
+
             for i, model in enumerate(v.models):
-                models = {}
-                models[model] = v.models[model]
+                model_dict = v.models[model]
                 messages = [XOSProcessor._find_message_by_model_name(v.messages, model)]
 
                 rendered[model] = template.render(
                     {
                         "proto": {
-                            "message_table": models,
+                            "message_table": {model: model_dict},
                             "messages": messages,
                             "policies": v.policies,
                             "message_names": [m["name"] for m in v.messages],
@@ -366,14 +353,28 @@
                         "options": v.options,
                     }
                 )
-            if str(v.options.get("legacy", "false")).strip('"').lower() == "true":
-                suffix = "_decl." + args.dest_extension
-            else:
-                suffix = "." + args.dest_extension
-            XOSProcessor._write_file_per_model(
-                rendered, args.output, suffix, args.quiet
-            )
+                if not rendered[model]:
+                    print("Not saving model %s as it is empty" % model, file=sys.stderr)
+                else:
+                    legacy = jinja2_extensions.base.xproto_list_evaluates_true(
+                        [model_dict.get("options", {}).get("custom_python", None),
+                         model_dict.get("options", {}).get("legacy", None),
+                         v.options.get("custom_python", None),
+                         v.options.get("legacy", None)])
+
+                    if legacy:
+                        file_name = "%s/%s_decl.%s" % (args.output, model.lower(), args.dest_extension)
+                    else:
+                        file_name = "%s/%s.%s" % (args.output, model.lower(), args.dest_extension)
+
+                    file = open(file_name, "w")
+                    file.write(rendered[model])
+                    file.close()
+                    if not args.quiet:
+                        print("Saved: %s" % file_name, file=sys.stderr)
         else:
+            # Handle the case where all models are written to the same python file.
+
             rendered = template.render(
                 {
                     "proto": {
diff --git a/lib/xos-genx/xosgenx/jinja2_extensions/base.py b/lib/xos-genx/xosgenx/jinja2_extensions/base.py
index fd4808e..c8f5bfe 100644
--- a/lib/xos-genx/xosgenx/jinja2_extensions/base.py
+++ b/lib/xos-genx/xosgenx/jinja2_extensions/base.py
@@ -15,6 +15,7 @@
 from __future__ import absolute_import, print_function
 import pdb
 import re
+from jinja2.runtime import Undefined
 from inflect import engine as inflect_engine_class
 
 inflect_engine = inflect_engine_class()
@@ -94,9 +95,12 @@
 
 
 def xproto_first_non_empty(lst):
-    for l in lst:
-        if l:
-            return l
+    # Returns the first non-empty element in the list. Empty is interpreted to be either
+    # None or the empty string or an instance of jinja2 Undefined(). The value False and the
+    # string "False" are not considered empty, but are values.
+    for item in lst:
+        if (item is not None) and (item != "") and (not isinstance(item, Undefined)):
+            return item
 
 
 def xproto_api_type(field):
@@ -481,3 +485,10 @@
     if x is True or (x == "True") or (x == '"True"'):
         return True
     return False
+
+
+def xproto_list_evaluates_true(lst):
+    # Returns True if the first non-empty item in the list is interpreted
+    # as True.
+    x = xproto_first_non_empty(lst)
+    return xproto_is_true(x)
diff --git a/lib/xos-genx/xosgenx/targets/django.xtarget b/lib/xos-genx/xosgenx/targets/django.xtarget
index 1c06de3..081fb5f 100644
--- a/lib/xos-genx/xosgenx/targets/django.xtarget
+++ b/lib/xos-genx/xosgenx/targets/django.xtarget
@@ -1,22 +1,16 @@
-{%- if options.legacy =='"True"' -%}
+{% for m in proto.messages %}{% if not m.options.skip_django -%}
+{%- if xproto_list_evaluates_true([m.options.custom_python, m.options.legacy, options.custom_python, options.legacy]) -%}
 {%- set legacy_tag = '_decl' -%}
 {%- set legacy = True -%}
 {%- else -%}
 {%- set legacy_tag = '' -%}
 {%- set legacy = False -%}
 {%- endif -%}
-{% for m in proto.messages %}{% if not m.options.skip_django -%}
-{% if legacy %}
-{# handle models that use custom headers rather than deriving from xosbase #}
 {% if m.options.custom_header %}
 from {{ m.options.custom_header|replace('"','') }} import *
 {% else %}
 from core.models.xosbase import *
 {% endif %}
-{% else %}
-{% if file_exists(xproto_base_name(m.name)|lower+'_header.py') -%}from {{xproto_base_name(m.name)|lower }}_header import *{%- else -%}from header import *{% endif %}
-{% if file_exists(xproto_base_name(m.name)|lower+'_top.py') -%}{{ include_file(xproto_base_name(m.name)|lower+'_top.py') }} {% endif %}
-{% endif %}
 
 {%- for l in m.links %}
 
@@ -41,7 +35,7 @@
 {{ xproto_fol_to_python_validator(policy, proto.policies[policy], m, error) }}
 {% endfor %}
 
-class {{ m.name }}{{ legacy_tag }}{{ xproto_base_def(m.name, m.bases) }}:
+class {{ m.name }}_decl{{ xproto_base_def(m.name, m.bases) }}:
   plural_name = "{{ xproto_pluralize(m) }}"
 
   {%- set feedback_state_fields = xproto_optioned_fields_to_list(xproto_base_fields(m, proto.message_table) + m.fields, 'feedback_state', 'True')  %}
@@ -105,7 +99,7 @@
       {% for policy,error in xproto_validations(m.options) %}
       policy_{{policy}}_validator(self, None)
       {% endfor %}
-      super({{ m.name }}{{ legacy_tag }}, self).save(*args, **kwds)
+      super({{ m.name }}_decl, self).save(*args, **kwds)
 
   def can_access(self, ctx):
       {% if m.policy %}
@@ -117,6 +111,14 @@
       {% endif %}
       
   {% endif %}
-    
+
+{# To maintain compatibility with migrations, we need to ensure that both the _decl and the non-_decl model #}
+{# exist. So we automatically create all models as _decl, and then add these trivial stubs #}
+{% if not legacy %}
+class {{ m.name }}({{ m. name }}_decl):
+    class Meta:
+        proxy = True
+{% endif %}
+
 {% if file_exists(xproto_base_name(m.name)|lower+'_bottom.py') -%}{{ include_file(xproto_base_name(m.name)|lower+'_bottom.py') }}{% endif %}
 {% endif %}{% endfor %}
diff --git a/lib/xos-genx/xosgenx/targets/service.xtarget b/lib/xos-genx/xosgenx/targets/service.xtarget
index 4c47fab..2061219 100644
--- a/lib/xos-genx/xosgenx/targets/service.xtarget
+++ b/lib/xos-genx/xosgenx/targets/service.xtarget
@@ -1,18 +1,6 @@
-{% if options.legacy =='"True"' -%}
-{% set legacy_tag = '_decl' %}
-{% set legacy = True %}
 from core.models.xosbase import *
 from core.models import ServiceInstance
-{% else %}
-{% set legacy = False %}
-{% set legacy_tag = '' %}
-{% if file_exists('../header.py') or file_exists('header.py')-%}from header import *
-{% else %}
-from core.models.xosbase import *
-from core.models import ServiceInstance
-{% endif %}
-{% endif %}
-
+{% set ns=namespace(any_legacy_tag = '') %}
 {% for m in proto.messages %}
 {% if file_exists(m.name|lower+'_header.py') -%}from {{m.name|lower }}_header import *{% endif %}
 {% if file_exists(m.name|lower+'_top.py') -%}{{ include_file(m.name|lower+'_top.py') }} {% endif %}
@@ -37,8 +25,22 @@
 
 {% endfor %}
 
+{# Compute any_legacy_tag by looking to see if any model in the service has legacy sete #}
 {% for m in proto.messages %}
-class {{ m.name }}{{ legacy_tag }}{{ xproto_base_def(m.name, m.bases, legacy_tag, proto.message_names) }}:
+{%- if xproto_list_evaluates_true([m.options.custom_python, m.options.legacy, options.custom_python, options.legacy]) -%}
+{% set ns.any_legacy_tag = '_decl' %}
+{% endif %}
+{% endfor %}
+
+{% for m in proto.messages %}
+{%- if xproto_list_evaluates_true([m.options.custom_python, m.options.legacy, options.custom_python, options.legacy]) -%}
+{% set legacy_tag = '_decl' %}
+{% set legacy = True %}
+{% else %}
+{% set legacy = False %}
+{% set legacy_tag = '' %}
+{% endif %}
+class {{ m.name }}{{ ns.any_legacy_tag }}{{ xproto_base_def(m.name, m.bases, legacy_tag, proto.message_names) }}:
   plural_name = "{{ xproto_pluralize(m) }}"
 
   {%- set feedback_state_fields = xproto_optioned_fields_to_list(xproto_base_fields(m, proto.message_table) + m.fields, 'feedback_state', 'True')  %}
@@ -95,7 +97,7 @@
           self.full_clean()
 
       if not base_save_in_attic:
-          super({{ m.name }}{{ legacy_tag }}, self).save(*args, **kwds)
+          super({{ m.name }}{{ ns.any_legacy_tag }}, self).save(*args, **kwds)
   
   def can_access(self, ctx):
       {% if m.policy %}
@@ -106,6 +108,14 @@
       return verdict,"xos_default_policy"
       {% endif %}
 
+{# To maintain compatibility with migrations, we need to ensure that both the _decl and the non-_decl model #}
+{# exist. So we automatically create all models as _decl, and then add these trivial stubs #}
+{% if (not legacy) and (ns.any_legacy_tag) %}
+class {{ m.name }}({{ m. name }}{{ ns.any_legacy_tag }}):
+    class Meta:
+        proxy = True
+{% endif %}
+
 {% if file_exists(m.name|lower+'_bottom.py') -%}{{ include_file(m.name|lower+'_bottom.py') }}{% endif %} 
 {% endfor %}
-+++ models{{ legacy_tag }}.py
++++ models{{ ns.any_legacy_tag }}.py