diff --git a/Makefile b/Makefile
index 52744744b..b178aeb8d 100644
--- a/Makefile
+++ b/Makefile
@@ -139,6 +139,10 @@ test-python-sdk: typecheck format prepare-aidbox-runme lint generate-python-sdk
          . venv/bin/activate && \
          python -m pytest test_sdk.py -v
 
+	cd $(PYTHON_EXAMPLE) && \
+         . venv/bin/activate && \
+         python -m pytest test_raw_extension.py -v
+
 test-python-fhirpy-sdk: typecheck format prepare-aidbox-runme lint generate-python-sdk-fhirpy python-fhirpy-test-setup
     # Run mypy in strict mode
 	cd $(PYTHON_FHIRPY_EXAMPLE) && \
diff --git a/examples/python/__snapshots__/patient_with_extensions.json b/examples/python/__snapshots__/patient_with_extensions.json
new file mode 100644
index 000000000..21ad5d912
--- /dev/null
+++ b/examples/python/__snapshots__/patient_with_extensions.json
@@ -0,0 +1,92 @@
+{
+  "_birthDate": {
+    "extension": [
+      {
+        "url": "http://hl7.org/fhir/StructureDefinition/patient-birthTime",
+        "valueDateTime": "1990-03-15T08:22:00-05:00"
+      }
+    ]
+  },
+  "birthDate": "1990-03-15",
+  "contact": [
+    {
+      "extension": [
+        {
+          "url": "http://example.org/fhir/StructureDefinition/contact-priority",
+          "valueInteger": 1
+        }
+      ],
+      "name": {
+        "family": "Watson",
+        "given": [
+          "John"
+        ]
+      },
+      "telecom": [
+        {
+          "system": "phone",
+          "value": "+44-20-7946-1234"
+        }
+      ]
+    }
+  ],
+  "extension": [
+    {
+      "url": "http://hl7.org/fhir/StructureDefinition/patient-birthPlace",
+      "valueAddress": {
+        "city": "Springfield",
+        "country": "US"
+      }
+    }
+  ],
+  "id": "ext-demo",
+  "modifierExtension": [
+    {
+      "url": "http://example.org/fhir/StructureDefinition/do-not-contact",
+      "valueBoolean": false
+    }
+  ],
+  "name": [
+    {
+      "_family": {
+        "extension": [
+          {
+            "url": "http://hl7.org/fhir/StructureDefinition/humanname-own-prefix",
+            "valueString": "van"
+          }
+        ]
+      },
+      "_given": [
+        {
+          "extension": [
+            {
+              "url": "http://example.org/fhir/StructureDefinition/name-source",
+              "valueCode": "birth-certificate"
+            }
+          ]
+        },
+        null,
+        {
+          "extension": [
+            {
+              "url": "http://example.org/fhir/StructureDefinition/name-source",
+              "valueCode": "baptism-record"
+            }
+          ]
+        }
+      ],
+      "extension": [
+        {
+          "url": "http://example.org/fhir/StructureDefinition/name-verified",
+          "valueBoolean": true
+        }
+      ],
+      "family": "van Beethoven",
+      "given": [
+        "Ludwig",
+        "Maria",
+        "Johann"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/examples/python/fhir_types/README.md b/examples/python/fhir_types/README.md
index d0c799301..c0fa5c311 100644
--- a/examples/python/fhir_types/README.md
+++ b/examples/python/fhir_types/README.md
@@ -2,21 +2,6 @@
 
 ## Package: `hl7.fhir.r4.core`
 
-### Modified Canonicals
-
-#### `http://hl7.org/fhir/StructureDefinition/BackboneElement`
-
-Skipped fields:
-
-- `modifierExtension`
-
-#### `http://hl7.org/fhir/StructureDefinition/DomainResource`
-
-Skipped fields:
-
-- `extension`
-- `modifierExtension`
-
 ### Skipped Canonicals
 
 - `http://fhir-registry.smarthealthit.org/StructureDefinition/capabilities`
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/base.py b/examples/python/fhir_types/hl7_fhir_r4_core/base.py
index a68278f58..50cb6ce07 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/base.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/base.py
@@ -14,29 +14,44 @@ class Element(BaseModel):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     extension: PyList[Extension] | None = Field(None, alias="extension", serialization_alias="extension")
     id: str | None = Field(None, alias="id", serialization_alias="id")
+    id_extension: Element | None = Field(None, alias="_id", serialization_alias="_id")
 
 
 class Address(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     city: str | None = Field(None, alias="city", serialization_alias="city")
+    city_extension: Element | None = Field(None, alias="_city", serialization_alias="_city")
     country: str | None = Field(None, alias="country", serialization_alias="country")
+    country_extension: Element | None = Field(None, alias="_country", serialization_alias="_country")
     district: str | None = Field(None, alias="district", serialization_alias="district")
+    district_extension: Element | None = Field(None, alias="_district", serialization_alias="_district")
     line: PyList[str] | None = Field(None, alias="line", serialization_alias="line")
+    line_extension: PyList[Element | None] | None = Field(None, alias="_line", serialization_alias="_line")
     period: Period | None = Field(None, alias="period", serialization_alias="period")
     postal_code: str | None = Field(None, alias="postalCode", serialization_alias="postalCode")
+    postal_code_extension: Element | None = Field(None, alias="_postalCode", serialization_alias="_postalCode")
     state: str | None = Field(None, alias="state", serialization_alias="state")
+    state_extension: Element | None = Field(None, alias="_state", serialization_alias="_state")
     text: str | None = Field(None, alias="text", serialization_alias="text")
+    text_extension: Element | None = Field(None, alias="_text", serialization_alias="_text")
     type: Literal["postal", "physical", "both"] | None = Field(None, alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
     use: Literal["home", "work", "temp", "old", "billing"] | None = Field(None, alias="use", serialization_alias="use")
+    use_extension: Element | None = Field(None, alias="_use", serialization_alias="_use")
 
 
 class Quantity(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     code: str | None = Field(None, alias="code", serialization_alias="code")
+    code_extension: Element | None = Field(None, alias="_code", serialization_alias="_code")
     comparator: Literal["<", "<=", ">=", ">"] | None = Field(None, alias="comparator", serialization_alias="comparator")
+    comparator_extension: Element | None = Field(None, alias="_comparator", serialization_alias="_comparator")
     system: str | None = Field(None, alias="system", serialization_alias="system")
+    system_extension: Element | None = Field(None, alias="_system", serialization_alias="_system")
     unit: str | None = Field(None, alias="unit", serialization_alias="unit")
+    unit_extension: Element | None = Field(None, alias="_unit", serialization_alias="_unit")
     value: float | None = Field(None, alias="value", serialization_alias="value")
+    value_extension: Element | None = Field(None, alias="_value", serialization_alias="_value")
 
 
 class Age(Quantity):
@@ -48,44 +63,63 @@ class Annotation(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     author_reference: Reference | None = Field(None, alias="authorReference", serialization_alias="authorReference")
     author_string: str | None = Field(None, alias="authorString", serialization_alias="authorString")
+    author_string_extension: Element | None = Field(None, alias="_authorString", serialization_alias="_authorString")
     text: str = Field(alias="text", serialization_alias="text")
+    text_extension: Element | None = Field(None, alias="_text", serialization_alias="_text")
     time: str | None = Field(None, alias="time", serialization_alias="time")
+    time_extension: Element | None = Field(None, alias="_time", serialization_alias="_time")
 
 
 class Attachment(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     content_type: str | None = Field(None, alias="contentType", serialization_alias="contentType")
+    content_type_extension: Element | None = Field(None, alias="_contentType", serialization_alias="_contentType")
     creation: str | None = Field(None, alias="creation", serialization_alias="creation")
+    creation_extension: Element | None = Field(None, alias="_creation", serialization_alias="_creation")
     data: str | None = Field(None, alias="data", serialization_alias="data")
+    data_extension: Element | None = Field(None, alias="_data", serialization_alias="_data")
     hash: str | None = Field(None, alias="hash", serialization_alias="hash")
+    hash_extension: Element | None = Field(None, alias="_hash", serialization_alias="_hash")
     language: str | None = Field(None, alias="language", serialization_alias="language")
+    language_extension: Element | None = Field(None, alias="_language", serialization_alias="_language")
     size: int | None = Field(None, alias="size", serialization_alias="size")
+    size_extension: Element | None = Field(None, alias="_size", serialization_alias="_size")
     title: str | None = Field(None, alias="title", serialization_alias="title")
+    title_extension: Element | None = Field(None, alias="_title", serialization_alias="_title")
     url: str | None = Field(None, alias="url", serialization_alias="url")
+    url_extension: Element | None = Field(None, alias="_url", serialization_alias="_url")
 
 
 class BackboneElement(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
+    modifier_extension: PyList[Extension] | None = Field(None, alias="modifierExtension", serialization_alias="modifierExtension")
 
 
 class CodeableConcept(Element, Generic[T]):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     coding: PyList[Coding[T]] | None = Field(None, alias="coding", serialization_alias="coding")
     text: str | None = Field(None, alias="text", serialization_alias="text")
+    text_extension: Element | None = Field(None, alias="_text", serialization_alias="_text")
 
 
 class Coding(Element, Generic[T]):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     code: T | None = Field(None, alias="code", serialization_alias="code")
+    code_extension: Element | None = Field(None, alias="_code", serialization_alias="_code")
     display: str | None = Field(None, alias="display", serialization_alias="display")
+    display_extension: Element | None = Field(None, alias="_display", serialization_alias="_display")
     system: str | None = Field(None, alias="system", serialization_alias="system")
+    system_extension: Element | None = Field(None, alias="_system", serialization_alias="_system")
     user_selected: bool | None = Field(None, alias="userSelected", serialization_alias="userSelected")
+    user_selected_extension: Element | None = Field(None, alias="_userSelected", serialization_alias="_userSelected")
     version: str | None = Field(None, alias="version", serialization_alias="version")
+    version_extension: Element | None = Field(None, alias="_version", serialization_alias="_version")
 
 
 class ContactDetail(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     name: str | None = Field(None, alias="name", serialization_alias="name")
+    name_extension: Element | None = Field(None, alias="_name", serialization_alias="_name")
     telecom: PyList[ContactPoint] | None = Field(None, alias="telecom", serialization_alias="telecom")
 
 
@@ -93,16 +127,22 @@ class ContactPoint(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     period: Period | None = Field(None, alias="period", serialization_alias="period")
     rank: PositiveInt | None = Field(None, alias="rank", serialization_alias="rank")
+    rank_extension: Element | None = Field(None, alias="_rank", serialization_alias="_rank")
     system: Literal["phone", "fax", "email", "pager", "url", "sms", "other"] | None = Field(None, alias="system", serialization_alias="system")
+    system_extension: Element | None = Field(None, alias="_system", serialization_alias="_system")
     use: Literal["home", "work", "temp", "old", "mobile"] | None = Field(None, alias="use", serialization_alias="use")
+    use_extension: Element | None = Field(None, alias="_use", serialization_alias="_use")
     value: str | None = Field(None, alias="value", serialization_alias="value")
+    value_extension: Element | None = Field(None, alias="_value", serialization_alias="_value")
 
 
 class Contributor(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     contact: PyList[ContactDetail] | None = Field(None, alias="contact", serialization_alias="contact")
     name: str = Field(alias="name", serialization_alias="name")
+    name_extension: Element | None = Field(None, alias="_name", serialization_alias="_name")
     type: Literal["author", "editor", "reviewer", "endorser"] = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
 
 
 class Count(Quantity):
@@ -136,12 +176,16 @@ class DataRequirement(Element):
     code_filter: PyList[DataRequirementCodeFilter] | None = Field(None, alias="codeFilter", serialization_alias="codeFilter")
     date_filter: PyList[DataRequirementDateFilter] | None = Field(None, alias="dateFilter", serialization_alias="dateFilter")
     limit: PositiveInt | None = Field(None, alias="limit", serialization_alias="limit")
+    limit_extension: Element | None = Field(None, alias="_limit", serialization_alias="_limit")
     must_support: PyList[str] | None = Field(None, alias="mustSupport", serialization_alias="mustSupport")
+    must_support_extension: PyList[Element | None] | None = Field(None, alias="_mustSupport", serialization_alias="_mustSupport")
     profile: PyList[str] | None = Field(None, alias="profile", serialization_alias="profile")
+    profile_extension: PyList[Element | None] | None = Field(None, alias="_profile", serialization_alias="_profile")
     sort: PyList[DataRequirementSort] | None = Field(None, alias="sort", serialization_alias="sort")
     subject_codeable_concept: CodeableConcept | None = Field(None, alias="subjectCodeableConcept", serialization_alias="subjectCodeableConcept")
     subject_reference: Reference | None = Field(None, alias="subjectReference", serialization_alias="subjectReference")
     type: str = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
 
 
 class Distance(Quantity):
@@ -163,6 +207,7 @@ class Dosage(BackboneElement):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     additional_instruction: PyList[CodeableConcept] | None = Field(None, alias="additionalInstruction", serialization_alias="additionalInstruction")
     as_needed_boolean: bool | None = Field(None, alias="asNeededBoolean", serialization_alias="asNeededBoolean")
+    as_needed_boolean_extension: Element | None = Field(None, alias="_asNeededBoolean", serialization_alias="_asNeededBoolean")
     as_needed_codeable_concept: CodeableConcept | None = Field(None, alias="asNeededCodeableConcept", serialization_alias="asNeededCodeableConcept")
     dose_and_rate: PyList[DosageDoseAndRate] | None = Field(None, alias="doseAndRate", serialization_alias="doseAndRate")
     max_dose_per_administration: Quantity | None = Field(None, alias="maxDosePerAdministration", serialization_alias="maxDosePerAdministration")
@@ -170,10 +215,13 @@ class Dosage(BackboneElement):
     max_dose_per_period: Ratio | None = Field(None, alias="maxDosePerPeriod", serialization_alias="maxDosePerPeriod")
     method: CodeableConcept | None = Field(None, alias="method", serialization_alias="method")
     patient_instruction: str | None = Field(None, alias="patientInstruction", serialization_alias="patientInstruction")
+    patient_instruction_extension: Element | None = Field(None, alias="_patientInstruction", serialization_alias="_patientInstruction")
     route: CodeableConcept | None = Field(None, alias="route", serialization_alias="route")
     sequence: int | None = Field(None, alias="sequence", serialization_alias="sequence")
+    sequence_extension: Element | None = Field(None, alias="_sequence", serialization_alias="_sequence")
     site: CodeableConcept | None = Field(None, alias="site", serialization_alias="site")
     text: str | None = Field(None, alias="text", serialization_alias="text")
+    text_extension: Element | None = Field(None, alias="_text", serialization_alias="_text")
     timing: Timing | None = Field(None, alias="timing", serialization_alias="timing")
 
 
@@ -185,23 +233,33 @@ class Duration(Quantity):
 class Expression(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     description: str | None = Field(None, alias="description", serialization_alias="description")
+    description_extension: Element | None = Field(None, alias="_description", serialization_alias="_description")
     expression: str | None = Field(None, alias="expression", serialization_alias="expression")
+    expression_extension: Element | None = Field(None, alias="_expression", serialization_alias="_expression")
     language: str = Field(alias="language", serialization_alias="language")
+    language_extension: Element | None = Field(None, alias="_language", serialization_alias="_language")
     name: str | None = Field(None, alias="name", serialization_alias="name")
+    name_extension: Element | None = Field(None, alias="_name", serialization_alias="_name")
     reference: str | None = Field(None, alias="reference", serialization_alias="reference")
+    reference_extension: Element | None = Field(None, alias="_reference", serialization_alias="_reference")
 
 
 class Extension(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     url: str = Field(alias="url", serialization_alias="url")
+    url_extension: Element | None = Field(None, alias="_url", serialization_alias="_url")
     value_address: Address | None = Field(None, alias="valueAddress", serialization_alias="valueAddress")
     value_age: Age | None = Field(None, alias="valueAge", serialization_alias="valueAge")
     value_annotation: Annotation | None = Field(None, alias="valueAnnotation", serialization_alias="valueAnnotation")
     value_attachment: Attachment | None = Field(None, alias="valueAttachment", serialization_alias="valueAttachment")
     value_base64binary: str | None = Field(None, alias="valueBase64Binary", serialization_alias="valueBase64Binary")
+    value_base64binary_extension: Element | None = Field(None, alias="_valueBase64Binary", serialization_alias="_valueBase64Binary")
     value_boolean: bool | None = Field(None, alias="valueBoolean", serialization_alias="valueBoolean")
+    value_boolean_extension: Element | None = Field(None, alias="_valueBoolean", serialization_alias="_valueBoolean")
     value_canonical: str | None = Field(None, alias="valueCanonical", serialization_alias="valueCanonical")
+    value_canonical_extension: Element | None = Field(None, alias="_valueCanonical", serialization_alias="_valueCanonical")
     value_code: str | None = Field(None, alias="valueCode", serialization_alias="valueCode")
+    value_code_extension: Element | None = Field(None, alias="_valueCode", serialization_alias="_valueCode")
     value_codeable_concept: CodeableConcept | None = Field(None, alias="valueCodeableConcept", serialization_alias="valueCodeableConcept")
     value_coding: Coding | None = Field(None, alias="valueCoding", serialization_alias="valueCoding")
     value_contact_detail: ContactDetail | None = Field(None, alias="valueContactDetail", serialization_alias="valueContactDetail")
@@ -210,24 +268,33 @@ class Extension(Element):
     value_count: Count | None = Field(None, alias="valueCount", serialization_alias="valueCount")
     value_data_requirement: DataRequirement | None = Field(None, alias="valueDataRequirement", serialization_alias="valueDataRequirement")
     value_date: str | None = Field(None, alias="valueDate", serialization_alias="valueDate")
+    value_date_extension: Element | None = Field(None, alias="_valueDate", serialization_alias="_valueDate")
     value_date_time: str | None = Field(None, alias="valueDateTime", serialization_alias="valueDateTime")
+    value_date_time_extension: Element | None = Field(None, alias="_valueDateTime", serialization_alias="_valueDateTime")
     value_decimal: float | None = Field(None, alias="valueDecimal", serialization_alias="valueDecimal")
+    value_decimal_extension: Element | None = Field(None, alias="_valueDecimal", serialization_alias="_valueDecimal")
     value_distance: Distance | None = Field(None, alias="valueDistance", serialization_alias="valueDistance")
     value_dosage: Dosage | None = Field(None, alias="valueDosage", serialization_alias="valueDosage")
     value_duration: Duration | None = Field(None, alias="valueDuration", serialization_alias="valueDuration")
     value_expression: Expression | None = Field(None, alias="valueExpression", serialization_alias="valueExpression")
     value_human_name: HumanName | None = Field(None, alias="valueHumanName", serialization_alias="valueHumanName")
     value_id: str | None = Field(None, alias="valueId", serialization_alias="valueId")
+    value_id_extension: Element | None = Field(None, alias="_valueId", serialization_alias="_valueId")
     value_identifier: Identifier | None = Field(None, alias="valueIdentifier", serialization_alias="valueIdentifier")
     value_instant: str | None = Field(None, alias="valueInstant", serialization_alias="valueInstant")
+    value_instant_extension: Element | None = Field(None, alias="_valueInstant", serialization_alias="_valueInstant")
     value_integer: int | None = Field(None, alias="valueInteger", serialization_alias="valueInteger")
+    value_integer_extension: Element | None = Field(None, alias="_valueInteger", serialization_alias="_valueInteger")
     value_markdown: str | None = Field(None, alias="valueMarkdown", serialization_alias="valueMarkdown")
+    value_markdown_extension: Element | None = Field(None, alias="_valueMarkdown", serialization_alias="_valueMarkdown")
     value_meta: Meta | None = Field(None, alias="valueMeta", serialization_alias="valueMeta")
     value_money: Money | None = Field(None, alias="valueMoney", serialization_alias="valueMoney")
     value_oid: str | None = Field(None, alias="valueOid", serialization_alias="valueOid")
+    value_oid_extension: Element | None = Field(None, alias="_valueOid", serialization_alias="_valueOid")
     value_parameter_definition: ParameterDefinition | None = Field(None, alias="valueParameterDefinition", serialization_alias="valueParameterDefinition")
     value_period: Period | None = Field(None, alias="valuePeriod", serialization_alias="valuePeriod")
     value_positive_int: PositiveInt | None = Field(None, alias="valuePositiveInt", serialization_alias="valuePositiveInt")
+    value_positive_int_extension: Element | None = Field(None, alias="_valuePositiveInt", serialization_alias="_valuePositiveInt")
     value_quantity: Quantity | None = Field(None, alias="valueQuantity", serialization_alias="valueQuantity")
     value_range: Range | None = Field(None, alias="valueRange", serialization_alias="valueRange")
     value_ratio: Ratio | None = Field(None, alias="valueRatio", serialization_alias="valueRatio")
@@ -236,25 +303,37 @@ class Extension(Element):
     value_sampled_data: SampledData | None = Field(None, alias="valueSampledData", serialization_alias="valueSampledData")
     value_signature: Signature | None = Field(None, alias="valueSignature", serialization_alias="valueSignature")
     value_string: str | None = Field(None, alias="valueString", serialization_alias="valueString")
+    value_string_extension: Element | None = Field(None, alias="_valueString", serialization_alias="_valueString")
     value_time: str | None = Field(None, alias="valueTime", serialization_alias="valueTime")
+    value_time_extension: Element | None = Field(None, alias="_valueTime", serialization_alias="_valueTime")
     value_timing: Timing | None = Field(None, alias="valueTiming", serialization_alias="valueTiming")
     value_trigger_definition: TriggerDefinition | None = Field(None, alias="valueTriggerDefinition", serialization_alias="valueTriggerDefinition")
     value_unsigned_int: int | None = Field(None, alias="valueUnsignedInt", serialization_alias="valueUnsignedInt")
+    value_unsigned_int_extension: Element | None = Field(None, alias="_valueUnsignedInt", serialization_alias="_valueUnsignedInt")
     value_uri: str | None = Field(None, alias="valueUri", serialization_alias="valueUri")
+    value_uri_extension: Element | None = Field(None, alias="_valueUri", serialization_alias="_valueUri")
     value_url: str | None = Field(None, alias="valueUrl", serialization_alias="valueUrl")
+    value_url_extension: Element | None = Field(None, alias="_valueUrl", serialization_alias="_valueUrl")
     value_usage_context: UsageContext | None = Field(None, alias="valueUsageContext", serialization_alias="valueUsageContext")
     value_uuid: str | None = Field(None, alias="valueUuid", serialization_alias="valueUuid")
+    value_uuid_extension: Element | None = Field(None, alias="_valueUuid", serialization_alias="_valueUuid")
 
 
 class HumanName(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     family: str | None = Field(None, alias="family", serialization_alias="family")
+    family_extension: Element | None = Field(None, alias="_family", serialization_alias="_family")
     given: PyList[str] | None = Field(None, alias="given", serialization_alias="given")
+    given_extension: PyList[Element | None] | None = Field(None, alias="_given", serialization_alias="_given")
     period: Period | None = Field(None, alias="period", serialization_alias="period")
     prefix: PyList[str] | None = Field(None, alias="prefix", serialization_alias="prefix")
+    prefix_extension: PyList[Element | None] | None = Field(None, alias="_prefix", serialization_alias="_prefix")
     suffix: PyList[str] | None = Field(None, alias="suffix", serialization_alias="suffix")
+    suffix_extension: PyList[Element | None] | None = Field(None, alias="_suffix", serialization_alias="_suffix")
     text: str | None = Field(None, alias="text", serialization_alias="text")
+    text_extension: Element | None = Field(None, alias="_text", serialization_alias="_text")
     use: Literal["usual", "official", "temp", "nickname", "anonymous", "old", "maiden"] | None = Field(None, alias="use", serialization_alias="use")
+    use_extension: Element | None = Field(None, alias="_use", serialization_alias="_use")
 
 
 class Identifier(Element):
@@ -262,48 +341,68 @@ class Identifier(Element):
     assigner: Reference | None = Field(None, alias="assigner", serialization_alias="assigner")
     period: Period | None = Field(None, alias="period", serialization_alias="period")
     system: str | None = Field(None, alias="system", serialization_alias="system")
+    system_extension: Element | None = Field(None, alias="_system", serialization_alias="_system")
     type: CodeableConcept[Literal["DL", "PPN", "BRN", "MR", "MCN", "EN", "TAX", "NIIP", "PRN", "MD", "DR", "ACSN", "UDI", "SNO", "SB", "PLAC", "FILL", "JHN"] | str] | None = Field(None, alias="type", serialization_alias="type")
     use: Literal["usual", "official", "temp", "secondary", "old"] | None = Field(None, alias="use", serialization_alias="use")
+    use_extension: Element | None = Field(None, alias="_use", serialization_alias="_use")
     value: str | None = Field(None, alias="value", serialization_alias="value")
+    value_extension: Element | None = Field(None, alias="_value", serialization_alias="_value")
 
 
 class Meta(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     last_updated: str | None = Field(None, alias="lastUpdated", serialization_alias="lastUpdated")
+    last_updated_extension: Element | None = Field(None, alias="_lastUpdated", serialization_alias="_lastUpdated")
     profile: PyList[str] | None = Field(None, alias="profile", serialization_alias="profile")
+    profile_extension: PyList[Element | None] | None = Field(None, alias="_profile", serialization_alias="_profile")
     security: PyList[Coding] | None = Field(None, alias="security", serialization_alias="security")
     source: str | None = Field(None, alias="source", serialization_alias="source")
+    source_extension: Element | None = Field(None, alias="_source", serialization_alias="_source")
     tag: PyList[Coding] | None = Field(None, alias="tag", serialization_alias="tag")
     version_id: str | None = Field(None, alias="versionId", serialization_alias="versionId")
+    version_id_extension: Element | None = Field(None, alias="_versionId", serialization_alias="_versionId")
 
 
 class Money(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     currency: str | None = Field(None, alias="currency", serialization_alias="currency")
+    currency_extension: Element | None = Field(None, alias="_currency", serialization_alias="_currency")
     value: float | None = Field(None, alias="value", serialization_alias="value")
+    value_extension: Element | None = Field(None, alias="_value", serialization_alias="_value")
 
 
 class Narrative(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     div: str = Field(alias="div", serialization_alias="div")
+    div_extension: Element | None = Field(None, alias="_div", serialization_alias="_div")
     status: Literal["generated", "extensions", "additional", "empty"] = Field(alias="status", serialization_alias="status")
+    status_extension: Element | None = Field(None, alias="_status", serialization_alias="_status")
 
 
 class ParameterDefinition(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     documentation: str | None = Field(None, alias="documentation", serialization_alias="documentation")
+    documentation_extension: Element | None = Field(None, alias="_documentation", serialization_alias="_documentation")
     max: str | None = Field(None, alias="max", serialization_alias="max")
+    max_extension: Element | None = Field(None, alias="_max", serialization_alias="_max")
     min: int | None = Field(None, alias="min", serialization_alias="min")
+    min_extension: Element | None = Field(None, alias="_min", serialization_alias="_min")
     name: str | None = Field(None, alias="name", serialization_alias="name")
+    name_extension: Element | None = Field(None, alias="_name", serialization_alias="_name")
     profile: str | None = Field(None, alias="profile", serialization_alias="profile")
+    profile_extension: Element | None = Field(None, alias="_profile", serialization_alias="_profile")
     type: str = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
     use: Literal["in", "out"] = Field(alias="use", serialization_alias="use")
+    use_extension: Element | None = Field(None, alias="_use", serialization_alias="_use")
 
 
 class Period(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     end: str | None = Field(None, alias="end", serialization_alias="end")
+    end_extension: Element | None = Field(None, alias="_end", serialization_alias="_end")
     start: str | None = Field(None, alias="start", serialization_alias="start")
+    start_extension: Element | None = Field(None, alias="_start", serialization_alias="_start")
 
 
 class Range(Element):
@@ -321,41 +420,60 @@ class Ratio(Element):
 class Reference(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     display: str | None = Field(None, alias="display", serialization_alias="display")
+    display_extension: Element | None = Field(None, alias="_display", serialization_alias="_display")
     identifier: Identifier | None = Field(None, alias="identifier", serialization_alias="identifier")
     reference: str | None = Field(None, alias="reference", serialization_alias="reference")
+    reference_extension: Element | None = Field(None, alias="_reference", serialization_alias="_reference")
     type: str | None = Field(None, alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
 
 
 class RelatedArtifact(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     citation: str | None = Field(None, alias="citation", serialization_alias="citation")
+    citation_extension: Element | None = Field(None, alias="_citation", serialization_alias="_citation")
     display: str | None = Field(None, alias="display", serialization_alias="display")
+    display_extension: Element | None = Field(None, alias="_display", serialization_alias="_display")
     document: Attachment | None = Field(None, alias="document", serialization_alias="document")
     label: str | None = Field(None, alias="label", serialization_alias="label")
+    label_extension: Element | None = Field(None, alias="_label", serialization_alias="_label")
     resource: str | None = Field(None, alias="resource", serialization_alias="resource")
+    resource_extension: Element | None = Field(None, alias="_resource", serialization_alias="_resource")
     type: Literal["documentation", "justification", "citation", "predecessor", "successor", "derived-from", "depends-on", "composed-of"] = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
     url: str | None = Field(None, alias="url", serialization_alias="url")
+    url_extension: Element | None = Field(None, alias="_url", serialization_alias="_url")
 
 
 class SampledData(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     data: str | None = Field(None, alias="data", serialization_alias="data")
+    data_extension: Element | None = Field(None, alias="_data", serialization_alias="_data")
     dimensions: PositiveInt = Field(alias="dimensions", serialization_alias="dimensions")
+    dimensions_extension: Element | None = Field(None, alias="_dimensions", serialization_alias="_dimensions")
     factor: float | None = Field(None, alias="factor", serialization_alias="factor")
+    factor_extension: Element | None = Field(None, alias="_factor", serialization_alias="_factor")
     lower_limit: float | None = Field(None, alias="lowerLimit", serialization_alias="lowerLimit")
+    lower_limit_extension: Element | None = Field(None, alias="_lowerLimit", serialization_alias="_lowerLimit")
     origin: Quantity = Field(alias="origin", serialization_alias="origin")
     period: float = Field(alias="period", serialization_alias="period")
+    period_extension: Element | None = Field(None, alias="_period", serialization_alias="_period")
     upper_limit: float | None = Field(None, alias="upperLimit", serialization_alias="upperLimit")
+    upper_limit_extension: Element | None = Field(None, alias="_upperLimit", serialization_alias="_upperLimit")
 
 
 class Signature(Element):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     data: str | None = Field(None, alias="data", serialization_alias="data")
+    data_extension: Element | None = Field(None, alias="_data", serialization_alias="_data")
     on_behalf_of: Reference | None = Field(None, alias="onBehalfOf", serialization_alias="onBehalfOf")
     sig_format: str | None = Field(None, alias="sigFormat", serialization_alias="sigFormat")
+    sig_format_extension: Element | None = Field(None, alias="_sigFormat", serialization_alias="_sigFormat")
     target_format: str | None = Field(None, alias="targetFormat", serialization_alias="targetFormat")
+    target_format_extension: Element | None = Field(None, alias="_targetFormat", serialization_alias="_targetFormat")
     type: PyList[Coding[Literal["1.2.840.10065.1.12.1.1", "1.2.840.10065.1.12.1.2", "1.2.840.10065.1.12.1.3", "1.2.840.10065.1.12.1.4", "1.2.840.10065.1.12.1.5", "1.2.840.10065.1.12.1.6", "1.2.840.10065.1.12.1.7", "1.2.840.10065.1.12.1.8", "1.2.840.10065.1.12.1.9", "1.2.840.10065.1.12.1.10", "1.2.840.10065.1.12.1.11", "1.2.840.10065.1.12.1.12", "1.2.840.10065.1.12.1.13", "1.2.840.10065.1.12.1.14", "1.2.840.10065.1.12.1.15", "1.2.840.10065.1.12.1.16", "1.2.840.10065.1.12.1.17", "1.2.840.10065.1.12.1.18"] | str]] = Field(alias="type", serialization_alias="type")
     when: str = Field(alias="when", serialization_alias="when")
+    when_extension: Element | None = Field(None, alias="_when", serialization_alias="_when")
     who: Reference = Field(alias="who", serialization_alias="who")
 
 
@@ -384,6 +502,7 @@ class Timing(BackboneElement):
     model_config = ConfigDict(validate_by_name=True, serialize_by_alias=True, extra="forbid")
     code: CodeableConcept[Literal["BID", "TID", "QID", "AM", "PM", "QD", "QOD", "Q1H", "Q2H", "Q3H", "Q4H", "Q6H", "Q8H", "BED", "WK", "MO"] | str] | None = Field(None, alias="code", serialization_alias="code")
     event: PyList[str] | None = Field(None, alias="event", serialization_alias="event")
+    event_extension: PyList[Element | None] | None = Field(None, alias="_event", serialization_alias="_event")
     repeat: TimingRepeat | None = Field(None, alias="repeat", serialization_alias="repeat")
 
 
@@ -392,11 +511,15 @@ class TriggerDefinition(Element):
     condition: Expression | None = Field(None, alias="condition", serialization_alias="condition")
     data: PyList[DataRequirement] | None = Field(None, alias="data", serialization_alias="data")
     name: str | None = Field(None, alias="name", serialization_alias="name")
+    name_extension: Element | None = Field(None, alias="_name", serialization_alias="_name")
     timing_date: str | None = Field(None, alias="timingDate", serialization_alias="timingDate")
+    timing_date_extension: Element | None = Field(None, alias="_timingDate", serialization_alias="_timingDate")
     timing_date_time: str | None = Field(None, alias="timingDateTime", serialization_alias="timingDateTime")
+    timing_date_time_extension: Element | None = Field(None, alias="_timingDateTime", serialization_alias="_timingDateTime")
     timing_reference: Reference | None = Field(None, alias="timingReference", serialization_alias="timingReference")
     timing_timing: Timing | None = Field(None, alias="timingTiming", serialization_alias="timingTiming")
     type: Literal["named-event", "periodic", "data-changed", "data-added", "data-modified", "data-removed", "data-accessed", "data-access-ended"] = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
 
 
 class UsageContext(Element):
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/bundle.py b/examples/python/fhir_types/hl7_fhir_r4_core/bundle.py
index 6a91311fc..ed7c3303f 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/bundle.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/bundle.py
@@ -9,6 +9,7 @@
 from fhir_types.hl7_fhir_r4_core.base import BackboneElement, Identifier, Signature
 from fhir_types.hl7_fhir_r4_core.resource import Resource
 from fhir_types.hl7_fhir_r4_core.resource_families import ResourceFamily
+from fhir_types.hl7_fhir_r4_core.base import Element
 
 
 class BundleEntry(BackboneElement):
@@ -62,8 +63,11 @@ class Bundle(Resource):
     link: PyList[BundleLink] | None = Field(None, alias="link", serialization_alias="link")
     signature: Signature | None = Field(None, alias="signature", serialization_alias="signature")
     timestamp: str | None = Field(None, alias="timestamp", serialization_alias="timestamp")
+    timestamp_extension: Element | None = Field(None, alias="_timestamp", serialization_alias="_timestamp")
     total: int | None = Field(None, alias="total", serialization_alias="total")
+    total_extension: Element | None = Field(None, alias="_total", serialization_alias="_total")
     type: Literal["document", "message", "transaction", "transaction-response", "batch", "batch-response", "history", "searchset", "collection"] = Field(alias="type", serialization_alias="type")
+    type_extension: Element | None = Field(None, alias="_type", serialization_alias="_type")
 
     def to_json(self, indent: int | None = None) -> str:
         return self.model_dump_json(exclude_unset=True, exclude_none=True, indent=indent)
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/domain_resource.py b/examples/python/fhir_types/hl7_fhir_r4_core/domain_resource.py
index 865a8d0a3..9b9616e28 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/domain_resource.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/domain_resource.py
@@ -6,7 +6,7 @@
 from pydantic import BaseModel, ConfigDict, Field, PositiveInt
 from typing import List as PyList, Literal
 
-from fhir_types.hl7_fhir_r4_core.base import Narrative
+from fhir_types.hl7_fhir_r4_core.base import Extension, Narrative
 from fhir_types.hl7_fhir_r4_core.resource import Resource
 from fhir_types.hl7_fhir_r4_core.resource_families import ResourceFamily
 
@@ -21,6 +21,8 @@ class DomainResource(Resource):
         pattern='DomainResource'
     )
     contained: PyList[ResourceFamily] | None = Field(None, alias="contained", serialization_alias="contained")
+    extension: PyList[Extension] | None = Field(None, alias="extension", serialization_alias="extension")
+    modifier_extension: PyList[Extension] | None = Field(None, alias="modifierExtension", serialization_alias="modifierExtension")
     text: Narrative | None = Field(None, alias="text", serialization_alias="text")
 
     def to_json(self, indent: int | None = None) -> str:
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/observation.py b/examples/python/fhir_types/hl7_fhir_r4_core/observation.py
index 3ee3a4d4e..2c39f5bb7 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/observation.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/observation.py
@@ -12,6 +12,7 @@
 )
 from fhir_types.hl7_fhir_r4_core.domain_resource import DomainResource
 from fhir_types.hl7_fhir_r4_core.resource_families import DomainResourceFamily
+from fhir_types.hl7_fhir_r4_core.base import Element
 
 
 class ObservationComponent(BackboneElement):
@@ -60,7 +61,9 @@ class Observation(DomainResource):
     derived_from: PyList[Reference] | None = Field(None, alias="derivedFrom", serialization_alias="derivedFrom")
     device: Reference | None = Field(None, alias="device", serialization_alias="device")
     effective_date_time: str | None = Field(None, alias="effectiveDateTime", serialization_alias="effectiveDateTime")
+    effective_date_time_extension: Element | None = Field(None, alias="_effectiveDateTime", serialization_alias="_effectiveDateTime")
     effective_instant: str | None = Field(None, alias="effectiveInstant", serialization_alias="effectiveInstant")
+    effective_instant_extension: Element | None = Field(None, alias="_effectiveInstant", serialization_alias="_effectiveInstant")
     effective_period: Period | None = Field(None, alias="effectivePeriod", serialization_alias="effectivePeriod")
     effective_timing: Timing | None = Field(None, alias="effectiveTiming", serialization_alias="effectiveTiming")
     encounter: Reference | None = Field(None, alias="encounter", serialization_alias="encounter")
@@ -69,6 +72,7 @@ class Observation(DomainResource):
     identifier: PyList[Identifier] | None = Field(None, alias="identifier", serialization_alias="identifier")
     interpretation: PyList[CodeableConcept[Literal["_GeneticObservationInterpretation", "CAR", "Carrier", "_ObservationInterpretationChange", "B", "D", "U", "W", "_ObservationInterpretationExceptions", "<", ">", "AC", "IE", "QCF", "TOX", "_ObservationInterpretationNormality", "A", "AA", "HH", "LL", "H", "H>", "HU", "L", "L<", "LU", "N", "_ObservationInterpretationSusceptibility", "I", "MS", "NCL", "NS", "R", "SYN-R", "S", "SDD", "SYN-S", "VS", "EX", "HX", "LX", "HM", "ObservationInterpretationDetection", "IND", "E", "NEG", "ND", "POS", "DET", "ObservationInterpretationExpectation", "EXP", "UNE", "OBX", "ReactivityObservationInterpretation", "NR", "RR", "WR"] | str]] | None = Field(None, alias="interpretation", serialization_alias="interpretation")
     issued: str | None = Field(None, alias="issued", serialization_alias="issued")
+    issued_extension: Element | None = Field(None, alias="_issued", serialization_alias="_issued")
     method: CodeableConcept | None = Field(None, alias="method", serialization_alias="method")
     note: PyList[Annotation] | None = Field(None, alias="note", serialization_alias="note")
     part_of: PyList[Reference] | None = Field(None, alias="partOf", serialization_alias="partOf")
@@ -76,18 +80,24 @@ class Observation(DomainResource):
     reference_range: PyList[ObservationReferenceRange] | None = Field(None, alias="referenceRange", serialization_alias="referenceRange")
     specimen: Reference | None = Field(None, alias="specimen", serialization_alias="specimen")
     status: Literal["registered", "preliminary", "final", "amended", "corrected", "cancelled", "entered-in-error", "unknown"] = Field(alias="status", serialization_alias="status")
+    status_extension: Element | None = Field(None, alias="_status", serialization_alias="_status")
     subject: Reference | None = Field(None, alias="subject", serialization_alias="subject")
     value_boolean: bool | None = Field(None, alias="valueBoolean", serialization_alias="valueBoolean")
+    value_boolean_extension: Element | None = Field(None, alias="_valueBoolean", serialization_alias="_valueBoolean")
     value_codeable_concept: CodeableConcept | None = Field(None, alias="valueCodeableConcept", serialization_alias="valueCodeableConcept")
     value_date_time: str | None = Field(None, alias="valueDateTime", serialization_alias="valueDateTime")
+    value_date_time_extension: Element | None = Field(None, alias="_valueDateTime", serialization_alias="_valueDateTime")
     value_integer: int | None = Field(None, alias="valueInteger", serialization_alias="valueInteger")
+    value_integer_extension: Element | None = Field(None, alias="_valueInteger", serialization_alias="_valueInteger")
     value_period: Period | None = Field(None, alias="valuePeriod", serialization_alias="valuePeriod")
     value_quantity: Quantity | None = Field(None, alias="valueQuantity", serialization_alias="valueQuantity")
     value_range: Range | None = Field(None, alias="valueRange", serialization_alias="valueRange")
     value_ratio: Ratio | None = Field(None, alias="valueRatio", serialization_alias="valueRatio")
     value_sampled_data: SampledData | None = Field(None, alias="valueSampledData", serialization_alias="valueSampledData")
     value_string: str | None = Field(None, alias="valueString", serialization_alias="valueString")
+    value_string_extension: Element | None = Field(None, alias="_valueString", serialization_alias="_valueString")
     value_time: str | None = Field(None, alias="valueTime", serialization_alias="valueTime")
+    value_time_extension: Element | None = Field(None, alias="_valueTime", serialization_alias="_valueTime")
 
     def to_json(self, indent: int | None = None) -> str:
         return self.model_dump_json(exclude_unset=True, exclude_none=True, indent=indent)
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/patient.py b/examples/python/fhir_types/hl7_fhir_r4_core/patient.py
index 86758601b..fb719082c 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/patient.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/patient.py
@@ -11,6 +11,7 @@
 )
 from fhir_types.hl7_fhir_r4_core.domain_resource import DomainResource
 from fhir_types.hl7_fhir_r4_core.resource_families import DomainResourceFamily
+from fhir_types.hl7_fhir_r4_core.base import Element
 
 
 class PatientCommunication(BackboneElement):
@@ -44,20 +45,27 @@ class Patient(DomainResource):
         pattern='Patient'
     )
     active: bool | None = Field(None, alias="active", serialization_alias="active")
+    active_extension: Element | None = Field(None, alias="_active", serialization_alias="_active")
     address: PyList[Address] | None = Field(None, alias="address", serialization_alias="address")
     birth_date: str | None = Field(None, alias="birthDate", serialization_alias="birthDate")
+    birth_date_extension: Element | None = Field(None, alias="_birthDate", serialization_alias="_birthDate")
     communication: PyList[PatientCommunication] | None = Field(None, alias="communication", serialization_alias="communication")
     contact: PyList[PatientContact] | None = Field(None, alias="contact", serialization_alias="contact")
     deceased_boolean: bool | None = Field(None, alias="deceasedBoolean", serialization_alias="deceasedBoolean")
+    deceased_boolean_extension: Element | None = Field(None, alias="_deceasedBoolean", serialization_alias="_deceasedBoolean")
     deceased_date_time: str | None = Field(None, alias="deceasedDateTime", serialization_alias="deceasedDateTime")
+    deceased_date_time_extension: Element | None = Field(None, alias="_deceasedDateTime", serialization_alias="_deceasedDateTime")
     gender: Literal["male", "female", "other", "unknown"] | None = Field(None, alias="gender", serialization_alias="gender")
+    gender_extension: Element | None = Field(None, alias="_gender", serialization_alias="_gender")
     general_practitioner: PyList[Reference] | None = Field(None, alias="generalPractitioner", serialization_alias="generalPractitioner")
     identifier: PyList[Identifier] | None = Field(None, alias="identifier", serialization_alias="identifier")
     link: PyList[PatientLink] | None = Field(None, alias="link", serialization_alias="link")
     managing_organization: Reference | None = Field(None, alias="managingOrganization", serialization_alias="managingOrganization")
     marital_status: CodeableConcept[Literal["A", "D", "I", "L", "M", "P", "S", "T", "U", "W", "UNK"] | str] | None = Field(None, alias="maritalStatus", serialization_alias="maritalStatus")
     multiple_birth_boolean: bool | None = Field(None, alias="multipleBirthBoolean", serialization_alias="multipleBirthBoolean")
+    multiple_birth_boolean_extension: Element | None = Field(None, alias="_multipleBirthBoolean", serialization_alias="_multipleBirthBoolean")
     multiple_birth_integer: int | None = Field(None, alias="multipleBirthInteger", serialization_alias="multipleBirthInteger")
+    multiple_birth_integer_extension: Element | None = Field(None, alias="_multipleBirthInteger", serialization_alias="_multipleBirthInteger")
     name: PyList[HumanName] | None = Field(None, alias="name", serialization_alias="name")
     photo: PyList[Attachment] | None = Field(None, alias="photo", serialization_alias="photo")
     telecom: PyList[ContactPoint] | None = Field(None, alias="telecom", serialization_alias="telecom")
diff --git a/examples/python/fhir_types/hl7_fhir_r4_core/resource.py b/examples/python/fhir_types/hl7_fhir_r4_core/resource.py
index 910f9ef1a..94e3e4c11 100644
--- a/examples/python/fhir_types/hl7_fhir_r4_core/resource.py
+++ b/examples/python/fhir_types/hl7_fhir_r4_core/resource.py
@@ -7,6 +7,7 @@
 from typing import List as PyList, Literal
 
 from fhir_types.hl7_fhir_r4_core.base import Meta
+from fhir_types.hl7_fhir_r4_core.base import Element
 
 
 class Resource(BaseModel):
@@ -19,8 +20,11 @@ class Resource(BaseModel):
         pattern='Resource'
     )
     id: str | None = Field(None, alias="id", serialization_alias="id")
+    id_extension: Element | None = Field(None, alias="_id", serialization_alias="_id")
     implicit_rules: str | None = Field(None, alias="implicitRules", serialization_alias="implicitRules")
+    implicit_rules_extension: Element | None = Field(None, alias="_implicitRules", serialization_alias="_implicitRules")
     language: str | None = Field(None, alias="language", serialization_alias="language")
+    language_extension: Element | None = Field(None, alias="_language", serialization_alias="_language")
     meta: Meta | None = Field(None, alias="meta", serialization_alias="meta")
 
     def to_json(self, indent: int | None = None) -> str:
diff --git a/examples/python/generate.ts b/examples/python/generate.ts
index e12f7782f..dbecdb04f 100644
--- a/examples/python/generate.ts
+++ b/examples/python/generate.ts
@@ -12,6 +12,7 @@ const builder = new APIBuilder({ logger })
     .fromPackage("hl7.fhir.r4.core", "4.0.1")
     .python({
         allowExtraFields: false,
+        primitiveTypeExtension: true,
         fhirpyClient: false,
         fieldFormat: "snake_case",
     })
@@ -20,12 +21,8 @@ const builder = new APIBuilder({ logger })
             "hl7.fhir.r4.core": {
                 "http://hl7.org/fhir/StructureDefinition/Bundle": {},
                 "http://hl7.org/fhir/StructureDefinition/OperationOutcome": {},
-                "http://hl7.org/fhir/StructureDefinition/DomainResource": {
-                    ignoreFields: ["extension", "modifierExtension"],
-                },
-                "http://hl7.org/fhir/StructureDefinition/BackboneElement": {
-                    ignoreFields: ["modifierExtension"],
-                },
+                "http://hl7.org/fhir/StructureDefinition/DomainResource": {},
+                "http://hl7.org/fhir/StructureDefinition/BackboneElement": {},
                 "http://hl7.org/fhir/StructureDefinition/Element": {},
                 "http://hl7.org/fhir/StructureDefinition/Patient": {},
                 "http://hl7.org/fhir/StructureDefinition/Observation": {},
diff --git a/examples/python/test_raw_extension.py b/examples/python/test_raw_extension.py
new file mode 100644
index 000000000..f530b7c82
--- /dev/null
+++ b/examples/python/test_raw_extension.py
@@ -0,0 +1,164 @@
+"""
+FHIR R4 Extension Demo Test
+
+Mirrors examples/typescript-r4/raw-extension.test.ts for the Python generator.
+"""
+
+import json
+from pathlib import Path
+
+from fhir_types.hl7_fhir_r4_core import (
+    Address,
+    ContactPoint,
+    Element,
+    Extension,
+    HumanName,
+)
+from fhir_types.hl7_fhir_r4_core.patient import Patient, PatientContact
+
+
+def create_patient_with_extensions() -> Patient:
+    name = HumanName(
+        extension=[
+            Extension(
+                url="http://example.org/fhir/StructureDefinition/name-verified",
+                value_boolean=True,
+            )
+        ],
+        family="van Beethoven",
+        family_extension=Element(
+            extension=[
+                Extension(
+                    url="http://hl7.org/fhir/StructureDefinition/humanname-own-prefix",
+                    value_string="van",
+                ),
+            ],
+        ),
+        given=["Ludwig", "Maria", "Johann"],
+        given_extension=[
+            Element(
+                extension=[
+                    Extension(
+                        url="http://example.org/fhir/StructureDefinition/name-source",
+                        value_code="birth-certificate",
+                    ),
+                ],
+            ),
+            None,
+            Element(
+                extension=[
+                    Extension(
+                        url="http://example.org/fhir/StructureDefinition/name-source",
+                        value_code="baptism-record",
+                    ),
+                ],
+            ),
+        ],
+    )
+
+    contact = PatientContact(
+        extension=[
+            Extension(
+                url="http://example.org/fhir/StructureDefinition/contact-priority",
+                value_integer=1,
+            )
+        ],
+        name=HumanName(family="Watson", given=["John"]),
+        telecom=[ContactPoint(system="phone", value="+44-20-7946-1234")],
+    )
+
+    return Patient(
+        id="ext-demo",
+        extension=[
+            Extension(
+                url="http://hl7.org/fhir/StructureDefinition/patient-birthPlace",
+                value_address=Address(city="Springfield", country="US"),
+            ),
+        ],
+        modifier_extension=[
+            Extension(
+                url="http://example.org/fhir/StructureDefinition/do-not-contact",
+                value_boolean=False,
+            ),
+        ],
+        birth_date="1990-03-15",
+        birth_date_extension=Element(
+            extension=[
+                Extension(
+                    url="http://hl7.org/fhir/StructureDefinition/patient-birthTime",
+                    value_date_time="1990-03-15T08:22:00-05:00",
+                ),
+            ],
+        ),
+        name=[name],
+        contact=[contact],
+    )
+
+
+SNAPSHOT_DIR = Path(__file__).parent / "__snapshots__"
+
+
+def test_patient_with_extensions() -> None:
+    patient = create_patient_with_extensions()
+    actual = json.loads(patient.to_json(indent=2))
+    expected = json.loads((SNAPSHOT_DIR / "patient_with_extensions.json").read_text())
+    assert actual == expected
+
+
+def test_read_resource_level_extension() -> None:
+    patient = create_patient_with_extensions()
+
+    assert patient.extension is not None
+    assert patient.extension[0].url == "http://hl7.org/fhir/StructureDefinition/patient-birthPlace"
+    assert patient.extension[0].value_address is not None
+    assert patient.extension[0].value_address.city == "Springfield"
+
+    assert patient.modifier_extension is not None
+    assert patient.modifier_extension[0].value_boolean is False
+
+
+def test_read_element_level_extension() -> None:
+    patient = create_patient_with_extensions()
+
+    assert patient.name is not None
+    name = patient.name[0]
+    assert name.extension is not None
+    assert name.extension[0].url == "http://example.org/fhir/StructureDefinition/name-verified"
+    assert name.extension[0].value_boolean is True
+
+    assert patient.contact is not None
+    contact = patient.contact[0]
+    assert contact.extension is not None
+    assert contact.extension[0].value_integer == 1
+
+
+def test_read_primitive_extension() -> None:
+    patient = create_patient_with_extensions()
+
+    name = patient.name[0]
+    assert isinstance(name.family_extension, Element)
+    assert name.family_extension.extension[0].value_string == "van"
+
+    assert isinstance(name.given_extension, list)
+    assert name.given_extension[0].extension[0].value_code == "birth-certificate"
+    assert name.given_extension[1] is None
+    assert name.given_extension[2].extension[0].value_code == "baptism-record"
+
+    assert patient.birth_date_extension is not None
+    assert isinstance(patient.birth_date_extension, Element)
+    assert patient.birth_date_extension.extension[0].value_date_time == "1990-03-15T08:22:00-05:00"
+
+
+def test_primitive_extension_survives_round_trip() -> None:
+    """After serialize → deserialize, typed _extension fields come back as Element instances."""
+    patient = create_patient_with_extensions()
+    restored = Patient.from_json(patient.to_json())
+
+    assert restored.birth_date == "1990-03-15"
+    assert restored.extension is not None
+    assert restored.extension[0].value_address is not None
+    assert restored.extension[0].value_address.city == "Springfield"
+
+    assert restored.birth_date_extension is not None
+    assert isinstance(restored.birth_date_extension, Element)
+    assert restored.birth_date_extension.extension[0].value_date_time == "1990-03-15T08:22:00-05:00"
diff --git a/src/api/builder.ts b/src/api/builder.ts
index 3bbac89a9..0ecf033fd 100644
--- a/src/api/builder.ts
+++ b/src/api/builder.ts
@@ -254,6 +254,7 @@ export class APIBuilder {
             ...defaultWriterOpts,
             rootPackageName: "fhir_types",
             fieldFormat: "snake_case",
+            primitiveTypeExtension: false,
         };
 
         const opts: PythonGeneratorOptions = {
diff --git a/src/api/writer-generator/python.ts b/src/api/writer-generator/python.ts
index 40f69e54e..3f0e43914 100644
--- a/src/api/writer-generator/python.ts
+++ b/src/api/writer-generator/python.ts
@@ -6,9 +6,12 @@ import { camelCase, pascalCase, snakeCase, uppercaseFirstLetterOfEach } from "@r
 import { Writer, type WriterOptions } from "@root/api/writer-generator/writer.ts";
 import { groupByPackages, sortAsDeclarationSequence, type TypeSchemaIndex } from "@root/typeschema/utils";
 import {
+    type CanonicalUrl,
     type EnumDefinition,
     type Field,
+    isPrimitiveIdentifier,
     isResourceTypeSchema,
+    isSpecializationTypeSchema,
     type NestedTypeSchema,
     type SpecializationTypeSchema,
     type TypeIdentifier,
@@ -99,6 +102,7 @@ const pyEnumType = (enumDef: EnumDefinition): string => {
 
 export interface PythonGeneratorOptions extends WriterOptions {
     allowExtraFields?: boolean;
+    primitiveTypeExtension?: boolean;
     rootPackageName: string; /// e.g. <rootPackageName>.hl7_fhir_r4_core.Patient.
     fieldFormat: StringFormatKey;
     fhirpyClient?: boolean;
@@ -476,15 +480,38 @@ export class Python extends Writer<PythonGeneratorOptions> {
 
     private generateFields(schema: SpecializationTypeSchema | NestedTypeSchema, schemaName: string): void {
         const sortedFields = Object.entries(schema.fields ?? []).sort(([a], [b]) => a.localeCompare(b));
+        const withExtensions = this.shouldAddPrimitiveExtensions(schema);
 
         for (const [fieldName, field] of sortedFields) {
             if ("choices" in field && field.choices) continue;
 
             const fieldInfo = this.buildFieldInfo(fieldName, field, schemaName);
             this.line(`${fieldInfo.name}: ${fieldInfo.type}${fieldInfo.defaultValue}`);
+
+            if (withExtensions && "type" in field && isPrimitiveIdentifier(field.type)) {
+                this.addPrimitiveExtensionField(fieldName, field.array ?? false);
+            }
         }
     }
 
+    private shouldAddPrimitiveExtensions(schema: SpecializationTypeSchema | NestedTypeSchema): boolean {
+        if (!this.opts.primitiveTypeExtension) return false;
+        if (!isSpecializationTypeSchema(schema)) return false;
+        for (const field of Object.values(schema.fields ?? {})) {
+            if ("choices" in field && field.choices) continue;
+            if ("type" in field && isPrimitiveIdentifier(field.type)) return true;
+        }
+        return false;
+    }
+
+    private addPrimitiveExtensionField(fieldName: string, isArray: boolean): void {
+        const pyFieldName = this.nameFormatFunction(`${fieldName}Extension`);
+        const alias = `_${fieldName}`;
+        const typeExpr = isArray ? "PyList[Element | None] | None" : "Element | None";
+        const aliasSpec = `alias="${alias}", serialization_alias="${alias}"`;
+        this.line(`${pyFieldName}: ${typeExpr} = Field(None, ${aliasSpec})`);
+    }
+
     private buildFieldInfo(fieldName: string, field: Field, schemaName: string): FieldInfo {
         const pyFieldName = fixReservedWords(this.nameFormatFunction(fieldName));
         const fieldType = this.determineFieldType(field, fieldName, schemaName);
@@ -590,6 +617,21 @@ export class Python extends Writer<PythonGeneratorOptions> {
 
         this.importComplexTypeDependencies(schema.dependencies);
         this.importResourceDependencies(schema.dependencies);
+        this.importElementIfNeeded(schema);
+    }
+
+    private importElementIfNeeded(schema: SpecializationTypeSchema): void {
+        if (!this.shouldAddPrimitiveExtensions(schema)) return;
+        if (schema.identifier.name === "Element") return;
+        if (schema.dependencies?.find((d) => d.name === "Element")) return;
+
+        assert(this.tsIndex !== undefined);
+        const elementUrl = "http://hl7.org/fhir/StructureDefinition/Element" as CanonicalUrl;
+        const element = this.tsIndex.resolveByUrl(schema.identifier.package, elementUrl);
+        if (!element) return;
+
+        const pyPackage = this.pyPackage(element.identifier);
+        this.pyImportFrom(pyPackage, "Element");
     }
 
     private importComplexTypeDependencies(dependencies: TypeIdentifier[]): void {