diff --git a/packages/fhir-eswatini/package.json b/packages/fhir-eswatini/package.json
index 42eeb503bd..10ab792a03 100644
--- a/packages/fhir-eswatini/package.json
+++ b/packages/fhir-eswatini/package.json
@@ -15,7 +15,7 @@
   "type": "module",
   "fhir": {
     "specUrl": "http://172.209.216.154/definitions.json.zip",
-    "adaptorGeneratedDate": "2026-06-02T15:23:39.432Z",
+    "adaptorGeneratedDate": "2026-06-05T10:42:23.868Z",
     "generatorVersion": "0.7.9",
     "options": {
       "base": "fhir-4"
diff --git a/packages/fhir-eswatini/src/builders.ts b/packages/fhir-eswatini/src/builders.ts
index d341f22443..b3e41ae0f6 100644
--- a/packages/fhir-eswatini/src/builders.ts
+++ b/packages/fhir-eswatini/src/builders.ts
@@ -573,6 +573,7 @@ export function organization(type: any, props?: any) {
   * @public
   * @function
   * @param {object} props - Properties to apply to the resource (includes common and custom properties).
+  * @param {} [props._birthDate] - undefined
   * @param {boolean} [props.active] - Whether this patient's record is in active use
   * @param {Address} [props.address] - An address for the individual
   * @param {date} [props.birthDate] - Date of birth: YYYY-MM-DD
diff --git a/packages/fhir-eswatini/src/datatypes.ts b/packages/fhir-eswatini/src/datatypes.ts
index 8c610b36c2..4abe30dd66 100644
--- a/packages/fhir-eswatini/src/datatypes.ts
+++ b/packages/fhir-eswatini/src/datatypes.ts
@@ -7,6 +7,7 @@ export const {
   coding,
   composite,
   concept,
+  ensureConceptText,
   ext,
   extendSystemMap,
   extendValues,
diff --git a/packages/fhir-eswatini/src/profiles/SzPatient.ts b/packages/fhir-eswatini/src/profiles/SzPatient.ts
index aa253ef445..2f8d41c233 100644
--- a/packages/fhir-eswatini/src/profiles/SzPatient.ts
+++ b/packages/fhir-eswatini/src/profiles/SzPatient.ts
@@ -9,6 +9,7 @@ import type { builders as FHIR } from "@openfn/language-fhir-4";
 type MaybeArray<T> = T | T[];
 
 export type Patient_SzPatient_Props = {
+    _birthDate?: any;
     active?: boolean;
     address?: FHIR.Address[];
     birthDate?: string;
@@ -135,6 +136,37 @@ export default function(props: Partial<Patient_SzPatient_Props>) {
         }
     }
 
+    {
+        if (!_.isNil(props._birthDate)) {
+            if (_.isPlainObject(props._birthDate)) {
+                resource._birthDate = Object.assign({}, props._birthDate);
+            } else {
+                delete resource._birthDate;
+                resource._birthDate = {};
+
+                dt.addExtension(
+                    resource._birthDate,
+                    "http://hl7.org/fhir/StructureDefinition/patient-birthTime",
+                    props._birthDate
+                );
+            }
+        }
+
+        if (!_.isNil(props._birthTime)) {
+            delete resource._birthTime;
+
+            if (!resource._birthDate) {
+                resource._birthDate = {};
+            }
+
+            dt.addExtension(
+                resource._birthDate,
+                "http://hl7.org/fhir/StructureDefinition/patient-birthTime",
+                props._birthTime
+            );
+        }
+    }
+
     if (!_.isNil(props.deceased)) {
         delete resource.deceased;
         dt.composite(resource, "deceased", props.deceased);
diff --git a/packages/fhir-eswatini/test/resources/Patient.test.ts b/packages/fhir-eswatini/test/resources/Patient.test.ts
index 2f124d2e58..7431b738c2 100644
--- a/packages/fhir-eswatini/test/resources/Patient.test.ts
+++ b/packages/fhir-eswatini/test/resources/Patient.test.ts
@@ -439,4 +439,39 @@ describe('SzPatient', () => {
       valueDateTime: '2025-06-01T10:00:00Z',
     });
   });
+
+  it('should map _birthDate primitive extension shorthand', () => {
+    const resource = b.patient('SzPatient', {
+      birthDate: '10/07/1990',
+      _birthDate: '2000-01-01T14:35:45-05:00',
+    });
+
+    assert.deepEqual(resource.birthDate, '10/07/1990');
+    assert.deepEqual(resource._birthDate, {
+      extension: [
+        {
+          url: 'http://hl7.org/fhir/StructureDefinition/patient-birthTime',
+          valueDateTime: '2000-01-01T14:35:45-05:00',
+        },
+      ],
+    });
+  });
+
+  it('should map _birthTime shorthand into _birthDate extension', () => {
+    const resource = b.patient('SzPatient', {
+      birthDate: '10/07/1990',
+      _birthTime: '2000-01-01T14:35:45-05:00',
+    });
+
+    assert.deepEqual(resource.birthDate, '10/07/1990');
+    assert.deepEqual(resource._birthDate, {
+      extension: [
+        {
+          url: 'http://hl7.org/fhir/StructureDefinition/patient-birthTime',
+          valueDateTime: '2000-01-01T14:35:45-05:00',
+        },
+      ],
+    });
+    assert.equal(resource._birthTime, undefined);
+  });
 });
diff --git a/packages/fhir-eswatini/types/builders.d.ts b/packages/fhir-eswatini/types/builders.d.ts
index 381cbeb2d7..f027ecbbb1 100644
--- a/packages/fhir-eswatini/types/builders.d.ts
+++ b/packages/fhir-eswatini/types/builders.d.ts
@@ -461,6 +461,7 @@ declare type Organization_SzOrganization_Props = {
 };
 
 declare type Patient_SzPatient_Props = {
+    _birthDate?: any;
     active?: boolean;
     address?: builders.Address[];
     birthDate?: string;
@@ -676,6 +677,7 @@ declare const cc: (codings: (builders.Coding | [string, string, Omit<builders.Co
 declare const coding: typeof builders.coding;
 declare const composite: (object: any, key: any, value: any) => void;
 declare const concept: (codings: (builders.Coding | [string, string, Omit<builders.Coding, "system" | "code">?]) | (builders.Coding | [string, string, Omit<builders.Coding, "system" | "code">?])[], extra?: Omit<builders.CodeableConcept, "coding">) => builders.CodeableConcept;
+declare const ensureConceptText: (concept: any) => void;
 declare const ext: (url: string, value: any, props?: Omit<builders.Extension, "url">) => {
     extension: ({
         url: string;
@@ -1058,6 +1060,7 @@ declare function organization(props: Organization_SzOrganization_Props): any;
   * @public
   * @function
   * @param {object} props - Properties to apply to the resource (includes common and custom properties).
+  * @param {} [props._birthDate] - undefined
   * @param {boolean} [props.active] - Whether this patient's record is in active use
   * @param {Address} [props.address] - An address for the individual
   * @param {date} [props.birthDate] - Date of birth: YYYY-MM-DD
@@ -1239,5 +1242,5 @@ declare function serviceRequest(type: "SzReferral", props: ServiceRequest_SzRefe
 declare function specimen(type: "SzLabSpecimen", props: Specimen_SzLabSpecimen_Props): any;
 declare function specimen(props: Specimen_SzLabSpecimen_Props): any;
 
-export { addExtension, appointment, c, cc, coding, composite, concept, condition, encounter, episodeOfCare, ext, extendSystemMap, extendValues, extension, findExtension, id, identifier, location, lookupValue, mapSystems, mapValues, medication, medicationDispense, medicationRequest, observation, organization, patient, practitioner, procedure, ref, reference, serviceRequest, setSystemMap, setValues, specimen, value };
+export { addExtension, appointment, c, cc, coding, composite, concept, condition, encounter, ensureConceptText, episodeOfCare, ext, extendSystemMap, extendValues, extension, findExtension, id, identifier, location, lookupValue, mapSystems, mapValues, medication, medicationDispense, medicationRequest, observation, organization, patient, practitioner, procedure, ref, reference, serviceRequest, setSystemMap, setValues, specimen, value };
 
diff --git a/tools/generate-fhir/src/codegen/generate-types.ts b/tools/generate-fhir/src/codegen/generate-types.ts
index e3e63083d3..dfeb491573 100644
--- a/tools/generate-fhir/src/codegen/generate-types.ts
+++ b/tools/generate-fhir/src/codegen/generate-types.ts
@@ -53,6 +53,19 @@ export const generateType = (
       continue;
     }
 
+    // Primitive extension props (_birthDate etc) are typed as `any` --
+    // their content depends on which extensions are present
+    if ((s as any).isPrimitiveExtension) {
+      props.push(
+        b.tsPropertySignature(
+          b.identifier(key),
+          b.tsTypeAnnotation(b.tsAnyKeyword()),
+          true,
+        ),
+      );
+      continue;
+    }
+
     // TODO need to handle this stuff!
     // let type;
     // if (s.typeDef) {
diff --git a/tools/generate-fhir/src/generate-code.ts b/tools/generate-fhir/src/generate-code.ts
index b716d4ac76..dfe6142dee 100644
--- a/tools/generate-fhir/src/generate-code.ts
+++ b/tools/generate-fhir/src/generate-code.ts
@@ -600,10 +600,136 @@ const mapSimpleProp = (propName: string, mapping: Mapping, schema: Schema) => {
   return ifPropInInput(propName, [assignProp], elseStatement);
 };
 
+const mapPrimitiveTypeDef = (propName: string, schema: Schema) => {
+  // propName is the underscore prop, eg _birthDate
+  const primitivePropName = propName;
+  // Only retrieve extension-backed child props
+  const primitiveExtensions = Object.entries(schema.typeDef || {}).filter(
+    ([, spec]: [string, any]) => spec.extension,
+  );
+  const statements: StatementKind[] = [];
+
+  const inputPropRef = (name: string) => safelyRefProp(INPUT_NAME, name);
+  const resourcePropRef = (name: string) => safelyRefProp(RESOURCE_NAME, name);
+  const copyPrimitiveMetadata = (name: string) =>
+    b.expressionStatement(
+      b.assignmentExpression(
+        '=',
+        resourcePropRef(name),
+        b.callExpression(
+          b.memberExpression(b.identifier('Object'), b.identifier('assign')),
+          [b.objectExpression([]), inputPropRef(name)],
+        ),
+      ),
+    );
+  const createEmptyPrimitiveMetadata = (name: string) =>
+    b.expressionStatement(
+      b.assignmentExpression('=', resourcePropRef(name), b.objectExpression([])),
+    );
+  const addPrimitiveExtension = (
+    targetName: string,
+    sourceName: string,
+    url: string,
+  ) =>
+    b.expressionStatement(
+      b.callExpression(
+        b.memberExpression(b.identifier('dt'), b.identifier('addExtension')),
+        [resourcePropRef(targetName), b.stringLiteral(url), inputPropRef(sourceName)],
+      ),
+    );
+
+  if (primitiveExtensions.length === 1) {
+    const [[, spec]] = primitiveExtensions as [string, any][];
+    statements.push(
+      ifPropInInput(
+        primitivePropName,
+        [
+          b.ifStatement(
+            b.callExpression(
+              b.memberExpression(b.identifier('_'), b.identifier('isPlainObject')),
+              [inputPropRef(primitivePropName)],
+            ),
+            b.blockStatement([
+              // If the caller already passed primitive metadata, preserve it
+              copyPrimitiveMetadata(primitivePropName),
+            ]),
+            b.blockStatement([
+              // Otherwise treat the underscore value as shorthand for the single known extension
+              b.expressionStatement(
+                b.unaryExpression('delete', resourcePropRef(primitivePropName)),
+              ),
+              createEmptyPrimitiveMetadata(primitivePropName),
+              addPrimitiveExtension(
+                primitivePropName,
+                primitivePropName,
+                spec.extension.url,
+              ),
+            ]),
+          ),
+        ],
+      ),
+    );
+  } else {
+    statements.push(
+      ifPropInInput(
+        primitivePropName,
+        [
+          b.ifStatement(
+            b.callExpression(
+              b.memberExpression(b.identifier('_'), b.identifier('isPlainObject')),
+              [inputPropRef(primitivePropName)],
+            ),
+            b.blockStatement([
+              // Multiple extension choices: only pass through explicit primitive metadata objects
+              copyPrimitiveMetadata(primitivePropName),
+            ]),
+          ),
+        ],
+      ),
+    );
+  }
+
+  for (const [key, spec] of primitiveExtensions as [string, any][]) {
+    // Support shorthand child props like _birthTime and rewrite them into _birthDate.extension[]
+    const inputPropName = `_${key}`;
+    statements.push(
+      ifPropInInput(
+        inputPropName,
+        [
+          b.expressionStatement(
+            b.unaryExpression('delete', resourcePropRef(inputPropName)),
+          ),
+          b.ifStatement(
+            b.unaryExpression('!', resourcePropRef(primitivePropName)),
+            b.blockStatement([
+              // Create the primitive metadata container before appending extension shorthand
+              createEmptyPrimitiveMetadata(primitivePropName),
+            ]),
+          ),
+          addPrimitiveExtension(
+            primitivePropName,
+            inputPropName,
+            spec.extension.url,
+          ),
+        ],
+      ),
+    );
+  }
+
+  return b.blockStatement(statements);
+};
+
+const isPrimitiveTypeDefParent = (schema: Schema) =>
+  !!(schema as any).isPrimitiveExtension && !!(schema as any).typeDef;
+
 // map a type def (ie, a nested object) property by property
 // TODO this is designed to handle singleton and array types
 // The array stuff adds a lot of complication and I need tests on both formats
 const mapTypeDef = (propName: string, mapping: Mapping, schema: Schema) => {
+  if (isPrimitiveTypeDefParent(schema)) {
+    return mapPrimitiveTypeDef(propName, schema);
+  }
+
   const statements: any[] = [];
 
   statements.push(
diff --git a/tools/generate-fhir/src/generate-schema.ts b/tools/generate-fhir/src/generate-schema.ts
index 55074fb926..563c720c49 100644
--- a/tools/generate-fhir/src/generate-schema.ts
+++ b/tools/generate-fhir/src/generate-schema.ts
@@ -343,6 +343,7 @@ async function parseProp(
   data,
 ) {
   let [parent, prop] = path.split('.');
+  const isExtensionPath = prop === 'extension';
   // TODO skip if multiple dots
 
   if (/\[x\]/.test(prop)) {
@@ -366,7 +367,16 @@ async function parseProp(
   if (schema.props[parent]) {
     const def: PropDef = {};
 
-    if (!data.type || schema.props[parent].type.includes('date')) {
+    // Keep primitive props
+    const isExtensionChild = isExtensionPath;
+    const hasSlice = !!data.sliceName;
+    const parentTypes = schema.props[parent].type || [];
+    const isPrimitiveParent =
+      !schema.props[parent].typeDef &&
+      parentTypes.length > 0 &&
+      parentTypes.every(type => type[0] === type[0]?.toLowerCase());
+
+    if (!data.type || (isPrimitiveParent && !(isExtensionChild && hasSlice))) {
       return;
     }
 
@@ -384,7 +394,8 @@ async function parseProp(
       type.profile.length &&
       type.profile[0].match(/\/StructureDefinition/)
     ) {
-      const typeId = type.profile[0].split('/').at(-1);
+      const extensionUrl = type.profile[0].split('|')[0];
+      const typeId = extensionUrl.split('/').at(-1);
       const spec = fullSpec[typeId];
 
       if (spec) {
@@ -396,7 +407,11 @@ async function parseProp(
           // look for extension.value[x] in the spec
         };
       } else {
-        console.log('WARNING: spec not found for ', typeId);
+        // Some extension profiles are not in the downloaded spec
+        // The profile URL is still enough for codegen
+        def.extension = {
+          url: extensionUrl,
+        };
       }
     } else {
       simpleType = typeDefs[type.code] || type.code;
@@ -431,8 +446,19 @@ async function parseProp(
     // }
 
     if (Object.keys(def).length) {
-      schema.props[parent].typeDef ??= {};
-      schema.props[parent].typeDef[prop] = def;
+      if (isPrimitiveParent && isExtensionChild) {
+        // primitive extension slices go on a top-level _parent prop, eg _birthDate
+        const underscoreProp = `_${parent}`;
+        schema.props[underscoreProp] ??= {
+          type: [],
+          isPrimitiveExtension: true,
+          typeDef: {},
+        };
+        schema.props[underscoreProp].typeDef[prop] = def;
+      } else {
+        schema.props[parent].typeDef ??= {};
+        schema.props[parent].typeDef[prop] = def;
+      }
     }
   }
 }
diff --git a/tools/generate-fhir/test/generate-code.test.ts b/tools/generate-fhir/test/generate-code.test.ts
index cf86d70235..3e615f45ab 100644
--- a/tools/generate-fhir/test/generate-code.test.ts
+++ b/tools/generate-fhir/test/generate-code.test.ts
@@ -119,7 +119,7 @@ run('calls dt.identifier for Identifier type', t => {
   t.is(dt.identifier.calls, 1);
 });
 
-run('builds single reference', t => {
+test.serial('builds single reference', t => {
   const profile = {
     x: { type: ['Reference'] },
   };
@@ -177,6 +177,79 @@ run('builds typeDef with nested extension', t => {
   t.is(dt.addExtension.calls, 1);
 });
 
+run('builds primitive sibling extension from underscored slice input', t => {
+  const profile = {
+    birthDate: {
+      type: ['date'],
+      isArray: false,
+    },
+    _birthDate: {
+      type: [],
+      isArray: false,
+      isPrimitiveExtension: true,
+      typeDef: {
+        birthTime: {
+          extension: {
+            url: 'http://hl7.org/fhir/StructureDefinition/patient-birthTime',
+          },
+          type: 'dateTime',
+        },
+      },
+    },
+  };
+  const schema = generateBuilder('Patient', profile);
+  const builder = compileBuilder(schema);
+  const result = builder({
+    birthDate: '10/07/1990',
+    _birthTime: '10am',
+  });
+
+  t.is(result.birthDate, '10/07/1990');
+  t.is(result._birthTime, undefined);
+  t.is(
+    result._birthDate.extension[0].url,
+    'http://hl7.org/fhir/StructureDefinition/patient-birthTime'
+  );
+  t.is(result._birthDate.extension[0].value, '10am');
+  t.is(dt.addExtension.calls, 1);
+});
+
+run('builds primitive sibling extension from underscored parent shorthand', t => {
+  const profile = {
+    birthDate: {
+      type: ['date'],
+      isArray: false,
+    },
+    _birthDate: {
+      type: [],
+      isArray: false,
+      isPrimitiveExtension: true,
+      typeDef: {
+        text: {
+          extension: {
+            url: 'http://example.org/fhir/StructureDefinition/text',
+          },
+          type: 'string',
+        },
+      },
+    },
+  };
+  const schema = generateBuilder('Patient', profile);
+  const builder = compileBuilder(schema);
+  const result = builder({
+    birthDate: '10/07/1990',
+    _birthDate: '10 july',
+  });
+
+  t.is(result.birthDate, '10/07/1990');
+  t.is(
+    result._birthDate.extension[0].url,
+    'http://example.org/fhir/StructureDefinition/text'
+  );
+  t.is(result._birthDate.extension[0].value, '10 july');
+  t.is(dt.addExtension.calls, 1);
+});
+
 run('skips nil properties', t => {
   const profile = {
     x: { type: ['Reference'] },