diff --git a/src/course-outline/CourseOutline.test.tsx b/src/course-outline/CourseOutline.test.tsx
index bc97222ff7..80d161ae81 100644
--- a/src/course-outline/CourseOutline.test.tsx
+++ b/src/course-outline/CourseOutline.test.tsx
@@ -708,7 +708,7 @@ describe('<CourseOutline />', () => {
     const { findByLabelText } = renderComponent();
 
     axiosMock
-      .onPost(getCourseBlockApiUrl(courseId), {
+      .onPatch(getCourseBlockApiUrl(courseId), {
         metadata: {
           video_sharing_options: VIDEO_SHARING_OPTIONS.allOff,
         },
@@ -721,7 +721,7 @@ describe('<CourseOutline />', () => {
 
     // The video sharing POST is the one with the expected data.
     // Find it by data content rather than assuming a fixed index.
-    const videoSharingPost = axiosMock.history.post.find(
+    const videoSharingPost = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes('video_sharing_options'),
     );
     expect(videoSharingPost).toBeDefined();
@@ -738,7 +738,7 @@ describe('<CourseOutline />', () => {
     renderComponent();
 
     axiosMock
-      .onPost(getCourseBlockApiUrl(courseId), {
+      .onPatch(getCourseBlockApiUrl(courseId), {
         metadata: {
           video_sharing_options: VIDEO_SHARING_OPTIONS.allOff,
         },
@@ -749,7 +749,7 @@ describe('<CourseOutline />', () => {
       async () => fireEvent.change(optionDropdown, { target: { value: VIDEO_SHARING_OPTIONS.allOff } }),
     );
 
-    const videoSharingPost = axiosMock.history.post.find(
+    const videoSharingPost = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes('video_sharing_options'),
     );
     expect(videoSharingPost).toBeDefined();
@@ -955,7 +955,6 @@ describe('<CourseOutline />', () => {
     );
     expect(newUnitPost).toBeDefined();
     expect(JSON.parse(newUnitPost!.data)).toEqual({
-      type: COURSE_BLOCK_NAMES.vertical.id,
       category: COURSE_BLOCK_NAMES.vertical.id,
       parent_locator: subsection.id,
       display_name: COURSE_BLOCK_NAMES.vertical.name,
@@ -1065,7 +1064,7 @@ describe('<CourseOutline />', () => {
 
     axiosMock.reset();
     axiosMock
-      .onPost(getCourseBlockApiUrl(courseId), {
+      .onPatch(getCourseBlockApiUrl(courseId), {
         publish: 'republish',
         metadata: {
           highlights_enabled_for_messaging: true,
@@ -1178,7 +1177,7 @@ describe('<CourseOutline />', () => {
         .reply(200, courseLaunchMock);
       // Rename-specific handlers
       axiosMock
-        .onPost(getCourseItemApiUrl(item.id))
+        .onPatch(getCourseItemApiUrl(item.id))
         .reply(200, { dummy: 'value' });
 
       // mock section, subsection and unit name and check within the elements.
@@ -1213,7 +1212,7 @@ describe('<CourseOutline />', () => {
       fireEvent.change(editField, { target: { value: newName } });
       await user.keyboard('{enter}');
       expect(
-        axiosMock.history.post[axiosMock.history.post.length - 1].data,
+        axiosMock.history.patch[axiosMock.history.patch.length - 1].data,
       ).toBe(JSON.stringify({
         metadata: {
           display_name: newName,
@@ -1432,7 +1431,7 @@ describe('<CourseOutline />', () => {
       ).toHaveTextContent(cardHeaderMessages.statusBadgeDraft.defaultMessage);
 
       axiosMock
-        .onPost(getCourseItemApiUrl(item.id), {
+        .onPatch(getCourseItemApiUrl(item.id), {
           publish: 'make_public',
         })
         .reply(200, { dummy: 'value' });
@@ -1500,7 +1499,7 @@ describe('<CourseOutline />', () => {
     expect(releaseDatePicker).toHaveValue('08/10/2023');
 
     axiosMock
-      .onPost(getCourseItemApiUrl(section.id), {
+      .onPatch(getCourseItemApiUrl(section.id), {
         publish: 'republish',
         metadata: {
           visible_to_staff_only: true,
@@ -1521,7 +1520,7 @@ describe('<CourseOutline />', () => {
     const saveButton = await findByTestId('configure-save-button');
     await act(async () => fireEvent.click(saveButton));
 
-    const sectionCfgPost = axiosMock.history.post.find(
+    const sectionCfgPost = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes('visible_to_staff_only'),
     );
     expect(sectionCfgPost).toBeDefined();
@@ -1571,7 +1570,7 @@ describe('<CourseOutline />', () => {
     };
 
     axiosMock
-      .onPost(getCourseItemApiUrl(subsection.id), expectedRequestData)
+      .onPatch(getCourseItemApiUrl(subsection.id), expectedRequestData)
       .reply(200, { dummy: 'value' });
 
     const [currentSection] = await findAllByTestId('section-card');
@@ -1630,7 +1629,7 @@ describe('<CourseOutline />', () => {
     await user.click(saveButton);
 
     // verify request
-    const subCfgPost = axiosMock.history.post.find(
+    const subCfgPost = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes(expectedRequestData.graderType),
     );
     expect(subCfgPost).toBeDefined();
@@ -1698,7 +1697,7 @@ describe('<CourseOutline />', () => {
     };
 
     axiosMock
-      .onPost(getCourseItemApiUrl(subsection.id), expectedRequestData)
+      .onPatch(getCourseItemApiUrl(subsection.id), expectedRequestData)
       .reply(200, { dummy: 'value' });
 
     const [currentSection] = await findAllByTestId('section-card');
@@ -1775,7 +1774,7 @@ describe('<CourseOutline />', () => {
     await user.click(saveButton);
 
     // verify request
-    const cfgPosta = axiosMock.history.post.find(
+    const cfgPosta = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes(expectedRequestData.graderType),
     );
     expect(cfgPosta).toBeDefined();
@@ -1849,7 +1848,7 @@ describe('<CourseOutline />', () => {
     };
 
     axiosMock
-      .onPost(getCourseItemApiUrl(subsection.id), expectedRequestData)
+      .onPatch(getCourseItemApiUrl(subsection.id), expectedRequestData)
       .reply(200, { dummy: 'value' });
 
     const [currentSection] = await findAllByTestId('section-card');
@@ -1904,7 +1903,7 @@ describe('<CourseOutline />', () => {
     await user.click(saveButton);
 
     // verify request
-    const cfgPostb = axiosMock.history.post.find(
+    const cfgPostb = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes(expectedRequestData.graderType),
     );
     expect(cfgPostb).toBeDefined();
@@ -1960,7 +1959,7 @@ describe('<CourseOutline />', () => {
     };
 
     axiosMock
-      .onPost(getCourseItemApiUrl(subsection.id), expectedRequestData)
+      .onPatch(getCourseItemApiUrl(subsection.id), expectedRequestData)
       .reply(200, { dummy: 'value' });
 
     const [currentSection] = await findAllByTestId('section-card');
@@ -2016,7 +2015,7 @@ describe('<CourseOutline />', () => {
     await user.click(saveButton);
 
     // verify request
-    const cfgPostc = axiosMock.history.post.find(
+    const cfgPostc = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes(expectedRequestData.graderType),
     );
     expect(cfgPostc).toBeDefined();
@@ -2071,7 +2070,7 @@ describe('<CourseOutline />', () => {
     };
 
     axiosMock
-      .onPost(getCourseItemApiUrl(subsection.id), expectedRequestData)
+      .onPatch(getCourseItemApiUrl(subsection.id), expectedRequestData)
       .reply(200, { dummy: 'value' });
 
     const [, currentSection] = await findAllByTestId('section-card');
@@ -2125,7 +2124,7 @@ describe('<CourseOutline />', () => {
     await user.click(saveButton);
 
     // verify request
-    const noSpecialPost = axiosMock.history.post.find(
+    const noSpecialPost = axiosMock.history.patch.find(
       (entry: any) => entry.data && entry.data.includes(expectedRequestData.graderType),
     );
     expect(noSpecialPost).toBeDefined();
@@ -2169,7 +2168,7 @@ describe('<CourseOutline />', () => {
     const isVisibleToStaffOnly = true;
 
     axiosMock
-      .onPost(getCourseItemApiUrl(unit.id), {
+      .onPatch(getCourseItemApiUrl(unit.id), {
         publish: 'republish',
         metadata: {
           visible_to_staff_only: isVisibleToStaffOnly,
@@ -2297,7 +2296,7 @@ describe('<CourseOutline />', () => {
     ];
 
     axiosMock
-      .onPost(getCourseItemApiUrl(section.id), {
+      .onPatch(getCourseItemApiUrl(section.id), {
         publish: 'republish',
         metadata: {
           highlights,
diff --git a/src/course-outline/data/api.ts b/src/course-outline/data/api.ts
index 4a95b4d19b..40ecacd0c5 100644
--- a/src/course-outline/data/api.ts
+++ b/src/course-outline/data/api.ts
@@ -46,13 +46,19 @@ export const getCourseLaunchApiUrl = ({
 
 export const getCourseBlockApiUrl = (courseId: string) => {
   const formattedCourseId = courseIDtoBlockID(courseId);
-  return `${getApiBaseUrl()}/xblock/${formattedCourseId}`;
+  // FC-0118: v1 xblock REST detail URL for the course's root block.
+  return `${getApiBaseUrl()}/api/contentstore/v1/xblock/${formattedCourseId}/`;
 };
 
 export const getCourseReindexApiUrl = (reindexLink: string) => `${getApiBaseUrl()}${reindexLink}`;
-export const getXBlockBaseApiUrl = () => `${getApiBaseUrl()}/xblock/`;
-export const getCourseItemApiUrl = (itemId: string) => `${getXBlockBaseApiUrl()}${itemId}`;
-export const getXBlockApiUrl = (blockId: string) => `${getXBlockBaseApiUrl()}outline/${blockId}`;
+// FC-0118 (ADR 0028/0037): standardized v1 xblock REST endpoint. Collection URL
+// (POST here creates a block); detail URLs carry the trailing slash the DRF
+// DefaultRouter requires.
+export const getXBlockBaseApiUrl = () => `${getApiBaseUrl()}/api/contentstore/v1/xblock/`;
+export const getCourseItemApiUrl = (itemId: string) => `${getXBlockBaseApiUrl()}${itemId}/`;
+// The outline handler (`/xblock/outline/{id}`) is a separate legacy Studio route,
+// NOT part of the v1 REST viewset, so it keeps the legacy `/xblock/` base.
+export const getXBlockApiUrl = (blockId: string) => `${getApiBaseUrl()}/xblock/outline/${blockId}`;
 export const exportTags = (courseId: string) =>
   `${getApiBaseUrl()}/api/content_tagging/v1/object_tags/${courseId}/export/`;
 export const createDiscussionsTopicsUrl = (courseId: string) =>
@@ -163,7 +169,7 @@ export async function getCourseLaunch({
  */
 export async function enableCourseHighlightsEmails(courseId: string): Promise<object> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseBlockApiUrl(courseId), {
+    .patch(getCourseBlockApiUrl(courseId), {
       publish: 'republish',
       metadata: {
         highlights_enabled_for_messaging: true,
@@ -205,7 +211,7 @@ export async function updateCourseSectionHighlights(
   highlights: Array<string>,
 ): Promise<object> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseItemApiUrl(sectionId), {
+    .patch(getCourseItemApiUrl(sectionId), {
       publish: 'republish',
       metadata: {
         highlights,
@@ -220,7 +226,7 @@ export async function updateCourseSectionHighlights(
  */
 export async function publishCourseItem(itemId: string): Promise<CourseItemUpdateResult> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseItemApiUrl(itemId), {
+    .patch(getCourseItemApiUrl(itemId), {
       publish: 'make_public',
     });
 
@@ -232,7 +238,7 @@ export async function publishCourseItem(itemId: string): Promise<CourseItemUpdat
  */
 export async function configureCourseSection(variables: ConfigureSectionData): Promise<object> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseItemApiUrl(variables.sectionId), {
+    .patch(getCourseItemApiUrl(variables.sectionId), {
       publish: 'republish',
       metadata: {
         // The backend expects metadata.visible_to_staff_only to either true or null
@@ -304,7 +310,7 @@ export async function configureCourseSubsection(
   });
 
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseItemApiUrl(itemId), body);
+    .patch(getCourseItemApiUrl(itemId), body);
 
   return data;
 }
@@ -329,7 +335,8 @@ export async function configureCourseUnit(variables: ConfigureUnitData): Promise
   };
   const url = getCourseItemApiUrl(variables.unitId);
   const { data } = await getAuthenticatedHttpClient()
-    .post(url, body);
+    // FC-0118: legacy POST-as-update becomes PATCH (partial_update) on v1.
+    .patch(url, body);
 
   return camelCaseObject(data);
 }
@@ -342,7 +349,7 @@ export async function editItemDisplayName({ itemId, displayName }: {
   displayName: string;
 }): Promise<CourseItemUpdateResult> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseItemApiUrl(itemId), {
+    .patch(getCourseItemApiUrl(itemId), {
       metadata: {
         display_name: displayName,
       },
@@ -405,7 +412,9 @@ export async function createCourseXblock({
   libraryContentKey,
 }: CreateCourseXBlockType) {
   const body = {
-    type,
+    // FC-0118: `type` is intentionally not sent — the v1 strict serializer does
+    // not accept it and the backend only reads `category` (which falls back to
+    // `type` here). `library_content_key` is accepted by the v1 serializer.
     boilerplate,
     category: category || type,
     parent_locator: parentLocator,
@@ -461,7 +470,7 @@ export async function setVideoSharingOption(
   videoSharingOption: string,
 ): Promise<object> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getCourseBlockApiUrl(courseId), {
+    .patch(getCourseBlockApiUrl(courseId), {
       metadata: {
         video_sharing_options: videoSharingOption,
       },
diff --git a/src/course-outline/outline-sidebar/AddSidebar.test.tsx b/src/course-outline/outline-sidebar/AddSidebar.test.tsx
index 7d988cedc1..c2635a9240 100644
--- a/src/course-outline/outline-sidebar/AddSidebar.test.tsx
+++ b/src/course-outline/outline-sidebar/AddSidebar.test.tsx
@@ -298,21 +298,18 @@ describe('AddSidebar', () => {
     const unit = await screen.findByRole('button', { name: 'Unit' });
     await user.click(section);
     expect(axiosMock.history.post[0].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'chapter',
       category: 'chapter',
       parentLocator: 'block-v1:UNIX+UX1+2025_T3+type@course+block@course',
       displayName: 'Section',
     })));
     await user.click(subsection);
     expect(axiosMock.history.post[1].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'sequential',
       category: 'sequential',
       parentLocator: lastSection.id,
       displayName: 'Subsection',
     })));
     await user.click(unit);
     expect(axiosMock.history.post[2].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'vertical',
       category: 'vertical',
       parentLocator: lastSubsection.id,
       displayName: 'Unit',
@@ -337,14 +334,12 @@ describe('AddSidebar', () => {
     await waitFor(() => expect(axiosMock.history.post.length).toBeGreaterThan(1));
     // should add a section first
     expect(axiosMock.history.post[0].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'chapter',
       category: 'chapter',
       parentLocator: 'block-v1:UNIX+UX1+2025_T3+type@course+block@course',
       displayName: 'Section',
     })));
     // then subsection
     expect(axiosMock.history.post[1].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'sequential',
       category: 'sequential',
       parentLocator: sectionId,
       displayName: 'Subsection',
@@ -365,19 +360,16 @@ describe('AddSidebar', () => {
     const subsectionId = 'block-v1:UNIX+UX1+2025_T3+type@sequential+block@sequential234';
     const unitId = 'block-v1:UNIX+UX1+2025_T3+type@vertical+block@vertical2133';
     const sectionBody = snakeCaseKeys({
-      type: 'chapter',
       category: 'chapter',
       parentLocator: 'block-v1:UNIX+UX1+2025_T3+type@course+block@course',
       displayName: 'Section',
     });
     const subsectionBody = snakeCaseKeys({
-      type: 'sequential',
       category: 'sequential',
       parentLocator: sectionId,
       displayName: 'Subsection',
     });
     const unitBody = snakeCaseKeys({
-      type: 'vertical',
       category: 'vertical',
       parentLocator: subsectionId,
       displayName: 'Unit',
@@ -421,7 +413,6 @@ describe('AddSidebar', () => {
     // first one is unit as per mock
     await user.click(addBtns[0]);
     expect(axiosMock.history.post[0].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'library_v2',
       category: 'vertical',
       parentLocator: lastSubsection.id,
       libraryContentKey: searchResult.results[0].hits[0].usage_key,
@@ -429,7 +420,6 @@ describe('AddSidebar', () => {
     // second one is subsection as per mock
     await user.click(addBtns[1]);
     expect(axiosMock.history.post[1].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'library_v2',
       category: 'sequential',
       parentLocator: lastSection.id,
       libraryContentKey: searchResult.results[0].hits[1].usage_key,
@@ -437,7 +427,6 @@ describe('AddSidebar', () => {
     // third one is section as per mock
     await user.click(addBtns[2]);
     expect(axiosMock.history.post[2].data).toEqual(JSON.stringify(snakeCaseKeys({
-      type: 'library_v2',
       category: 'chapter',
       parentLocator: 'block-v1:UNIX+UX1+2025_T3+type@course+block@course',
       libraryContentKey: searchResult.results[0].hits[2].usage_key,
diff --git a/src/course-unit/CourseUnit.test.tsx b/src/course-unit/CourseUnit.test.tsx
index c3073affe7..1453b5610d 100644
--- a/src/course-unit/CourseUnit.test.tsx
+++ b/src/course-unit/CourseUnit.test.tsx
@@ -391,7 +391,7 @@ describe('<CourseUnit />', () => {
     await user.click(deleteButton);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -553,7 +553,7 @@ describe('<CourseUnit />', () => {
       .replyOnce(200, { locator: '1234567890' });
 
     axiosMock
-      .onPost(getCourseItemApiUrl(blockId), {
+      .onPatch(getCourseItemApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -677,7 +677,7 @@ describe('<CourseUnit />', () => {
     const newDisplayName = `${unitDisplayName} new`;
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         metadata: {
           display_name: newDisplayName,
         },
@@ -734,7 +734,7 @@ describe('<CourseUnit />', () => {
     const user = userEvent.setup();
     const { courseKey, locator } = courseCreateXblockMock;
     axiosMock
-      .onPost(postXBlockBaseApiUrl(), { type: 'video', category: 'video', parent_locator: blockId })
+      .onPost(postXBlockBaseApiUrl(), { category: 'video', parent_locator: blockId })
       .reply(500, {});
     render(<RootWrapper />);
 
@@ -749,12 +749,12 @@ describe('<CourseUnit />', () => {
   it('handle creating Problem xblock and showing editor modal', async () => {
     const user = userEvent.setup();
     axiosMock
-      .onPost(postXBlockBaseApiUrl(), { type: 'problem', category: 'problem', parent_locator: blockId })
+      .onPost(postXBlockBaseApiUrl(), { category: 'problem', parent_locator: blockId })
       .reply(200, courseCreateXblockMock);
     render(<RootWrapper />);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -914,7 +914,7 @@ describe('<CourseUnit />', () => {
     const newDisplayName = `${unitDisplayName} new`;
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         metadata: {
           display_name: newDisplayName,
         },
@@ -963,7 +963,7 @@ describe('<CourseUnit />', () => {
     const waffleSpy = mockWaffleFlags({ useVideoGalleryFlow: true });
 
     axiosMock
-      .onPost(postXBlockBaseApiUrl(), { type: 'video', category: 'video', parent_locator: blockId })
+      .onPost(postXBlockBaseApiUrl(), { category: 'video', parent_locator: blockId })
       .reply(200, courseCreateXblockMock);
     render(<RootWrapper />);
 
@@ -973,7 +973,7 @@ describe('<CourseUnit />', () => {
     await user.click(publishButton);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -1054,7 +1054,7 @@ describe('<CourseUnit />', () => {
 
   it('handles creating Video xblock and showing editor modal', async () => {
     axiosMock
-      .onPost(postXBlockBaseApiUrl(), { type: 'video', category: 'video', parent_locator: blockId })
+      .onPost(postXBlockBaseApiUrl(), { category: 'video', parent_locator: blockId })
       .reply(200, courseCreateXblockMock);
     const user = userEvent.setup();
     render(<RootWrapper />);
@@ -1064,7 +1064,7 @@ describe('<CourseUnit />', () => {
     );
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -1247,7 +1247,7 @@ describe('<CourseUnit />', () => {
     expect(visibilityCheckbox).not.toBeChecked();
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.republish,
         metadata: { visible_to_staff_only: true },
       })
@@ -1302,7 +1302,7 @@ describe('<CourseUnit />', () => {
     await user.click(makeVisibilityBtn);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.republish,
         metadata: { visible_to_staff_only: null },
       })
@@ -1346,7 +1346,7 @@ describe('<CourseUnit />', () => {
     });
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.makePublic,
       })
       .reply(200, { dummy: 'value' });
@@ -1428,7 +1428,7 @@ describe('<CourseUnit />', () => {
     });
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.discardChanges,
       })
       .reply(200, { dummy: 'value' });
@@ -1505,7 +1505,7 @@ describe('<CourseUnit />', () => {
     expect(group1Checkbox).toBeChecked();
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id), {
+      .onPatch(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id), {
         publish: 'republish',
         metadata: { visible_to_staff_only: true, group_access: { 50: [2] }, discussion_enabled: true },
       })
@@ -1996,7 +1996,7 @@ describe('<CourseUnit />', () => {
       render(<RootWrapper />);
 
       axiosMock
-        .onPatch(postXBlockBaseApiUrl())
+        .onPatch(getXBlockBaseApiUrl(blockId))
         .reply(200, {});
 
       axiosMock
@@ -2060,7 +2060,7 @@ describe('<CourseUnit />', () => {
       render(<RootWrapper />);
 
       axiosMock
-        .onPatch(postXBlockBaseApiUrl())
+        .onPatch(getXBlockBaseApiUrl(blockId))
         .reply(200, {});
 
       await executeThunk(
@@ -2114,7 +2114,7 @@ describe('<CourseUnit />', () => {
       render(<RootWrapper />);
 
       axiosMock
-        .onPatch(postXBlockBaseApiUrl())
+        .onPatch(getXBlockBaseApiUrl(blockId))
         .reply(200, {});
 
       await executeThunk(
@@ -2197,7 +2197,7 @@ describe('<CourseUnit />', () => {
     it('handles submit xblock restrict access data when save button is clicked', async () => {
       const user = userEvent.setup();
       axiosMock
-        .onPost(getXBlockBaseApiUrl(id), {
+        .onPatch(getXBlockBaseApiUrl(id), {
           publish: PUBLISH_TYPES.republish,
           metadata: { visible_to_staff_only: false, group_access: { 970807507: [1959537066] } },
         })
@@ -2251,8 +2251,8 @@ describe('<CourseUnit />', () => {
       await user.click(saveModalBtnText);
 
       await waitFor(() => {
-        expect(axiosMock.history.post.length).toBeGreaterThan(0);
-        expect(axiosMock.history.post[0].url).toBe(getXBlockBaseApiUrl(id));
+        expect(axiosMock.history.patch.length).toBeGreaterThan(0);
+        expect(axiosMock.history.patch[0].url).toBe(getXBlockBaseApiUrl(id));
       });
 
       expect(screen.queryByTestId('configure-modal')).not.toBeInTheDocument();
@@ -2698,7 +2698,7 @@ describe('<CourseUnit />', () => {
     await user.click(settingsTab);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.republish,
         metadata: { visible_to_staff_only: true, discussion_enabled: true },
       })
@@ -2730,7 +2730,7 @@ describe('<CourseUnit />', () => {
     expect(await screen.findByRole('heading', { name: /visible to staff only/i })).toBeInTheDocument();
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.republish,
         metadata: { visible_to_staff_only: null, discussion_enabled: true },
       })
@@ -2798,7 +2798,7 @@ describe('<CourseUnit />', () => {
     await user.click(settingsTab);
 
     axiosMock
-      .onPost(getXBlockBaseApiUrl(blockId), {
+      .onPatch(getXBlockBaseApiUrl(blockId), {
         publish: PUBLISH_TYPES.republish,
         metadata: {
           visible_to_staff_only: null,
@@ -2839,7 +2839,7 @@ describe('<CourseUnit />', () => {
         ...courseSectionVerticalMock,
       });
     axiosMock
-      .onPost(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id))
+      .onPatch(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id))
       .reply(200, {
         ...courseSectionVerticalMock,
       });
@@ -2898,11 +2898,11 @@ describe('<CourseUnit />', () => {
 
     // Check that the group access is being updated
     await waitFor(() => {
-      expect(axiosMock.history.post.length).toBeGreaterThan(0);
+      expect(axiosMock.history.patch.length).toBeGreaterThan(0);
     });
 
-    expect(axiosMock.history.post[0].url).toBe(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id));
-    expect(axiosMock.history.post[0].data).toMatch(/"group_access":\{"10":\[1,2\]\}/);
+    expect(axiosMock.history.patch[0].url).toBe(getXBlockBaseApiUrl(courseSectionVerticalMock.xblock_info.id));
+    expect(axiosMock.history.patch[0].data).toMatch(/"group_access":\{"10":\[1,2\]\}/);
   });
 
   it('should one group in the visibility field in the unit sidebar', async () => {
@@ -3360,7 +3360,6 @@ describe('<CourseUnit />', () => {
         expect(JSON.parse(axiosMock.history.post[0].data)).toMatchObject({
           category: blockType,
           parent_locator: blockId,
-          type: blockType,
         });
       });
     });
@@ -3432,7 +3431,6 @@ describe('<CourseUnit />', () => {
             category: blockType,
             parent_locator: blockId,
             boilerplate: template.boilerplate,
-            ...(blockType !== 'openassessment' ? { type: blockType } : {}),
           });
         });
       });
@@ -3464,7 +3462,6 @@ describe('<CourseUnit />', () => {
         expect(JSON.parse(axiosMock.history.post[0].data)).toMatchObject({
           category: blockType,
           parent_locator: blockId,
-          type: blockType,
         });
       });
     });
@@ -3489,7 +3486,6 @@ describe('<CourseUnit />', () => {
         category: 'html',
         parent_locator: blockId,
         library_content_key: 'lb:Axim:TEST:html:571fe018-f3ce-45c9-8f53-5dafcb422fdd',
-        type: 'library_v2',
       });
     });
   });
diff --git a/src/course-unit/data/api.ts b/src/course-unit/data/api.ts
index 609c4715a1..aa50547035 100644
--- a/src/course-unit/data/api.ts
+++ b/src/course-unit/data/api.ts
@@ -6,13 +6,18 @@ import { isUnitImportedFromLib, normalizeCourseSectionVerticalData, updateXBlock
 
 const getStudioBaseUrl = () => getConfig().STUDIO_BASE_URL;
 
-export const getXBlockBaseApiUrl = (itemId: string) => `${getStudioBaseUrl()}/xblock/${itemId}`;
+// FC-0118 (ADR 0028/0037): standardized v1 xblock REST endpoint. The trailing
+// slash is required by the DRF DefaultRouter that serves the v1 XblockViewSet
+// (the legacy `/xblock/{id}` route had none). Detail actions: GET (retrieve),
+// PUT/PATCH (update), DELETE (destroy).
+export const getXBlockBaseApiUrl = (itemId: string) => `${getStudioBaseUrl()}/api/contentstore/v1/xblock/${itemId}/`;
 export const getCourseSectionVerticalApiUrl = (itemId: string) =>
   `${getStudioBaseUrl()}/api/contentstore/v1/container_handler/${itemId}`;
 export const getCourseVerticalChildrenApiUrl = (itemId: string, getUpstreamInfo: boolean = false) =>
   `${getStudioBaseUrl()}/api/contentstore/v1/container/${itemId}/children?get_upstream_info=${getUpstreamInfo}`;
 export const getCourseOutlineInfoUrl = (courseId: string) => `${getStudioBaseUrl()}/course/${courseId}?format=concise`;
-export const postXBlockBaseApiUrl = () => `${getStudioBaseUrl()}/xblock/`;
+// FC-0118: v1 xblock collection endpoint — POST here creates a block.
+export const postXBlockBaseApiUrl = () => `${getStudioBaseUrl()}/api/contentstore/v1/xblock/`;
 export const libraryBlockChangesUrl = (blockId: string) =>
   `${getStudioBaseUrl()}/api/contentstore/v2/downstreams/${blockId}/sync`;
 
@@ -21,7 +26,8 @@ export const libraryBlockChangesUrl = (blockId: string) =>
  */
 export async function editUnitDisplayName(unitId: string, displayName: string): Promise<object> {
   const { data } = await getAuthenticatedHttpClient()
-    .post(getXBlockBaseApiUrl(unitId), {
+    // FC-0118: legacy POST-as-update becomes PATCH (partial_update) on v1.
+    .patch(getXBlockBaseApiUrl(unitId), {
       metadata: {
         display_name: displayName,
       },
@@ -94,8 +100,13 @@ export async function getCourseOutlineInfo(courseId: string): Promise<CourseOutl
  * Move a unit item to new unit.
  */
 export async function patchUnitItem(sourceLocator: string, targetParentLocator: string): Promise<MoveInfoData> {
+  // FC-0118: the move used to PATCH the legacy collection URL (`/xblock/`); the
+  // v1 REST viewset only exposes PATCH on the detail route, so we PATCH the
+  // source block's detail URL. `update_xblock_response` still routes to the
+  // move-item path off `move_source_locator` in the body (the URL key is used
+  // only to derive the course for the permission check).
   const { data } = await getAuthenticatedHttpClient()
-    .patch(postXBlockBaseApiUrl(), {
+    .patch(getXBlockBaseApiUrl(sourceLocator), {
       parent_locator: targetParentLocator,
       move_source_locator: sourceLocator,
     });
diff --git a/src/course-updates/data/api.js b/src/course-updates/data/api.js
index 4a528a506d..20ae08811e 100644
--- a/src/course-updates/data/api.js
+++ b/src/course-updates/data/api.js
@@ -7,7 +7,10 @@ export const updateCourseUpdatesApiUrl = (courseId, updateId) =>
   `${getApiBaseUrl()}/course_info_update/${courseId}/${updateId}`;
 export const getCourseHandoutApiUrl = (courseId) => {
   const formattedCourseId = courseId.split('course-v1:')[1];
-  return `${getApiBaseUrl()}/xblock/block-v1:${formattedCourseId}+type@course_info+block@handouts`;
+  // FC-0118 (ADR 0028/0037): standardized v1 xblock REST detail endpoint for the
+  // course handouts block. Trailing slash required by the DRF DefaultRouter;
+  // used by GET (retrieve) and PUT (full update).
+  return `${getApiBaseUrl()}/api/contentstore/v1/xblock/block-v1:${formattedCourseId}+type@course_info+block@handouts/`;
 };
 
 /**
diff --git a/src/custom-pages/CustomPages.test.tsx b/src/custom-pages/CustomPages.test.tsx
index 3fcd850422..57d8e2e488 100644
--- a/src/custom-pages/CustomPages.test.tsx
+++ b/src/custom-pages/CustomPages.test.tsx
@@ -110,9 +110,9 @@ describe('CustomPages', () => {
   });
 
   it('should add new page when "add a new page button" is clicked', async () => {
-    const xblockAddUrl = `${getApiBaseUrl()}/xblock/`;
+    const xblockAddUrl = `${getApiBaseUrl()}/api/contentstore/v1/xblock/`;
     axiosMock.onGet(getTabHandlerUrl(courseId)).reply(200, generateFetchPageApiResponse());
-    axiosMock.onPut(xblockAddUrl).reply(200, generateNewPageApiResponse());
+    axiosMock.onPost(xblockAddUrl).reply(200, generateNewPageApiResponse());
 
     renderComponent();
     const addButton = await screen.findByTestId('body-add-button');
@@ -121,7 +121,7 @@ describe('CustomPages', () => {
     fireEvent.click(addButton);
 
     await waitFor(() => {
-      expect(axiosMock.history.put.length).toBeGreaterThanOrEqual(1);
+      expect(axiosMock.history.post.length).toBeGreaterThanOrEqual(1);
     });
   });
 
@@ -166,7 +166,7 @@ describe('CustomPages', () => {
 
   it('should delete page on successful delete', async () => {
     const pageId = 'mOckID1';
-    const xblockEditUrl = `${getApiBaseUrl()}/xblock/${pageId}`;
+    const xblockEditUrl = `${getApiBaseUrl()}/api/contentstore/v1/xblock/${pageId}/`;
     axiosMock.onGet(getTabHandlerUrl(courseId)).reply(200, generateFetchPageApiResponse());
     axiosMock.onDelete(xblockEditUrl).reply(204);
 
@@ -182,7 +182,7 @@ describe('CustomPages', () => {
 
   it('should show error alert on delete failure', async () => {
     const pageId = 'mOckID1';
-    const xblockEditUrl = `${getApiBaseUrl()}/xblock/${pageId}`;
+    const xblockEditUrl = `${getApiBaseUrl()}/api/contentstore/v1/xblock/${pageId}/`;
     axiosMock.onGet(getTabHandlerUrl(courseId)).reply(200, generateFetchPageApiResponse());
     axiosMock.onDelete(xblockEditUrl).reply(500);
 
@@ -250,7 +250,7 @@ describe('CustomPages', () => {
 
   it('should save visibility on successful toggle', async () => {
     const pageId = 'mOckID1';
-    const xblockEditUrl = `${getApiBaseUrl()}/xblock/${pageId}`;
+    const xblockEditUrl = `${getApiBaseUrl()}/api/contentstore/v1/xblock/${pageId}/`;
     axiosMock.onGet(getTabHandlerUrl(courseId)).reply(200, generateFetchPageApiResponse());
     axiosMock.onPut(xblockEditUrl).reply(200, {});
 
@@ -265,7 +265,7 @@ describe('CustomPages', () => {
 
   it('should show error alert on visibility save failure', async () => {
     const pageId = 'mOckID1';
-    const xblockEditUrl = `${getApiBaseUrl()}/xblock/${pageId}`;
+    const xblockEditUrl = `${getApiBaseUrl()}/api/contentstore/v1/xblock/${pageId}/`;
     axiosMock.onGet(getTabHandlerUrl(courseId)).reply(200, generateFetchPageApiResponse());
     axiosMock.onPut(xblockEditUrl).reply(500);
 
diff --git a/src/custom-pages/data/api.ts b/src/custom-pages/data/api.ts
index 2381e90912..431ad65109 100644
--- a/src/custom-pages/data/api.ts
+++ b/src/custom-pages/data/api.ts
@@ -29,8 +29,10 @@ export async function getCustomPages(courseId: string): Promise<CustomPage[]> {
  * Delete custom page for provided block.
  */
 export async function deleteCustomPage(blockId: string): Promise<void> {
+  // FC-0118 (ADR 0028/0037): standardized v1 xblock REST endpoint (trailing
+  // slash required by the DRF DefaultRouter).
   await getAuthenticatedHttpClient()
-    .delete(`${getApiBaseUrl()}/xblock/${blockId}`);
+    .delete(`${getApiBaseUrl()}/api/contentstore/v1/xblock/${blockId}/`);
 }
 
 /**
@@ -40,7 +42,9 @@ export async function addCustomPage(courseId: string): Promise<Record<string, un
   const v1CourseId = courseId.substring(7);
   const courseBlockId = `block-${v1CourseId}+type@course+block@course`;
   const { data } = await getAuthenticatedHttpClient()
-    .put(`${getApiBaseUrl()}/xblock/`, {
+    // FC-0118: creating a block is POST on the v1 collection endpoint (the
+    // legacy route accepted PUT here).
+    .post(`${getApiBaseUrl()}/api/contentstore/v1/xblock/`, {
       category: 'static_tab',
       parent_locator: courseBlockId,
     });
@@ -56,7 +60,8 @@ export async function updateCustomPage({ blockId, htmlString, metadata }: {
   metadata?: Record<string, unknown>;
 }): Promise<Record<string, unknown>> {
   const { data } = await getAuthenticatedHttpClient()
-    .put(`${getApiBaseUrl()}/xblock/${blockId}`, {
+    // FC-0118: PUT (full update) on the v1 detail endpoint (trailing slash).
+    .put(`${getApiBaseUrl()}/api/contentstore/v1/xblock/${blockId}/`, {
       id: blockId,
       data: htmlString,
       metadata,
diff --git a/src/editors/containers/PdfEditor/index.test.tsx b/src/editors/containers/PdfEditor/index.test.tsx
index 5e26a8dc70..bb1fdf064f 100644
--- a/src/editors/containers/PdfEditor/index.test.tsx
+++ b/src/editors/containers/PdfEditor/index.test.tsx
@@ -115,7 +115,7 @@ describe('PdfEditor', () => {
     expect(screen.queryAllByLabelText(downloadMessages.allowDownloadLabel.defaultMessage)).toEqual([]);
   });
   it('submits changes to the cms', async () => {
-    axiosMock.onPost('https://studio.local/xblock/pdf-block-id').reply(200, {
+    axiosMock.onPatch('https://studio.local/api/contentstore/v1/xblock/pdf-block-id/').reply(200, {
       data: {
         id: 'pdf-block-id',
         data: null,
@@ -136,8 +136,10 @@ describe('PdfEditor', () => {
     fireEvent.change(field, { target: { value: 'https://somewhere.com/stuff.pdf' } });
     const saveButton = screen.getByLabelText(editorMessages.saveButtonAriaLabel.defaultMessage);
     await user.click(saveButton);
-    await waitFor(() => expect(axiosMock.history.post[0].url).toEqual('https://studio.local/xblock/pdf-block-id'));
-    const request = axiosMock.history.post[0];
+    await waitFor(() =>
+      expect(axiosMock.history.patch[0].url).toEqual('https://studio.local/api/contentstore/v1/xblock/pdf-block-id/')
+    );
+    const request = axiosMock.history.patch[0];
     expect(JSON.parse(request.data).metadata.url).toEqual('https://somewhere.com/stuff.pdf');
   });
 });
diff --git a/src/editors/data/services/cms/api.test.ts b/src/editors/data/services/cms/api.test.ts
index 45a4bb4806..4f9c1bdbb8 100644
--- a/src/editors/data/services/cms/api.test.ts
+++ b/src/editors/data/services/cms/api.test.ts
@@ -4,11 +4,13 @@ import {
   get,
   post,
   put,
+  patch,
   deleteObject,
 } from './utils';
 
 jest.mock('./urls', () => ({
   block: jest.fn().mockReturnValue('urls.block'),
+  blockV1: jest.fn().mockReturnValue('urls.blockV1'),
   blockAncestor: jest.fn().mockReturnValue('urls.blockAncestor'),
   blockStudioView: jest.fn().mockReturnValue('urls.StudioView'),
   courseAssets: jest.fn().mockReturnValue('urls.courseAssets'),
@@ -34,6 +36,7 @@ jest.mock('./utils', () => ({
   get: jest.fn().mockName('get'),
   post: jest.fn().mockName('post'),
   put: jest.fn().mockName('put'),
+  patch: jest.fn().mockName('patch'),
   deleteObject: jest.fn().mockName('deleteObject'),
 }));
 
@@ -53,7 +56,7 @@ describe('cms api', () => {
     describe('fetchBlockId', () => {
       it('should call get with url.blocks', async () => {
         await apiMethods.fetchBlockById({ blockId, studioEndpointUrl });
-        expect(get).toHaveBeenCalledWith(urls.block({ blockId, studioEndpointUrl }));
+        expect(get).toHaveBeenCalledWith(urls.blockV1({ blockId, studioEndpointUrl }));
       });
     });
 
@@ -175,11 +178,9 @@ describe('cms api', () => {
           blockId,
           blockType: 'html',
           content,
-          learningContextId,
           title,
         })).toEqual({
           category: 'html',
-          courseKey: learningContextId,
           data: content,
           has_changes: true,
           id: blockId,
@@ -221,11 +222,9 @@ describe('cms api', () => {
           blockId,
           blockType: 'video',
           content,
-          learningContextId,
           title,
         })).toEqual({
           category: 'video',
-          courseKey: learningContextId,
           display_name: title,
           id: blockId,
           metadata: {
@@ -259,22 +258,20 @@ describe('cms api', () => {
     describe('saveBlock', () => {
       const content =
         'Im baby palo santo ugh celiac fashion axe. La croix lo-fi venmo whatever. Beard man braid migas single-origin coffee forage ramps.';
-      it('should call post with urls.block and normalizeContent', async () => {
+      it('should call patch with urls.blockV1 and normalizeContent', async () => {
         await apiMethods.saveBlock({
           blockId,
           blockType: 'html',
           content,
-          learningContextId,
           studioEndpointUrl,
           title,
         });
-        expect(post).toHaveBeenCalledWith(
-          urls.block({ studioEndpointUrl }),
+        expect(patch).toHaveBeenCalledWith(
+          urls.blockV1({ studioEndpointUrl, blockId }),
           apiMethods.normalizeContent({
             blockType: 'html',
             content,
             blockId,
-            learningContextId,
             title,
           }),
         );
diff --git a/src/editors/data/services/cms/api.ts b/src/editors/data/services/cms/api.ts
index dc33a8b9ec..dd9485f11b 100644
--- a/src/editors/data/services/cms/api.ts
+++ b/src/editors/data/services/cms/api.ts
@@ -6,6 +6,7 @@ import {
   get,
   post,
   put,
+  patch,
   deleteObject,
 } from './utils';
 import { durationStringFromValue } from '../../../containers/VideoEditor/components/VideoSettingsModal/components/DurationWidget/hooks';
@@ -113,7 +114,7 @@ export const processLicense = (licenseType, licenseDetails) => {
 export const apiMethods = {
   fetchBlockById: ({ blockId, studioEndpointUrl }): Promise<{ data: FieldsResponse; }> =>
     get(
-      urls.block({ blockId, studioEndpointUrl }),
+      urls.blockV1({ blockId, studioEndpointUrl }),
     ),
   /** A better name for this would be 'get ancestors of block' */
   fetchByUnitId: ({ blockId, studioEndpointUrl }): Promise<{ data: AncestorsResponse; }> =>
@@ -301,20 +302,17 @@ export const apiMethods = {
     blockId,
     blockType,
     content,
-    learningContextId,
     title,
   }: {
     blockId: string;
     blockType: string;
     content: any; // string for 'html' blocks, otherwise Record<string, any>
-    learningContextId: string;
     title: string;
   }) => {
     let response = {};
     if (blockType === 'html') {
       response = {
         category: blockType,
-        courseKey: learningContextId,
         data: content,
         has_changes: true,
         id: blockId,
@@ -324,7 +322,6 @@ export const apiMethods = {
       response = {
         data: content.olx,
         category: blockType,
-        courseKey: learningContextId,
         has_changes: true,
         id: blockId,
         metadata: { display_name: title, ...content.settings },
@@ -341,7 +338,6 @@ export const apiMethods = {
       });
       response = {
         category: blockType,
-        courseKey: learningContextId,
         display_name: title,
         id: blockId,
         metadata: {
@@ -364,7 +360,6 @@ export const apiMethods = {
     } else if (blockType === 'pdf') {
       response = {
         category: blockType,
-        courseKey: learningContextId,
         has_changes: true,
         id: blockId,
         metadata: { ...snakeCaseKeys(content), display_name: title },
@@ -378,17 +373,17 @@ export const apiMethods = {
     blockId,
     blockType,
     content,
-    learningContextId,
     studioEndpointUrl,
     title,
   }) =>
-    post(
-      urls.block({ studioEndpointUrl, blockId }),
+    // FC-0118: legacy POST-as-update becomes PATCH (partial_update) on the v1
+    // xblock REST detail endpoint.
+    patch(
+      urls.blockV1({ studioEndpointUrl, blockId }),
       apiMethods.normalizeContent({
         blockType,
         content,
         blockId,
-        learningContextId,
         title,
       }),
     ),
diff --git a/src/editors/data/services/cms/urls.test.ts b/src/editors/data/services/cms/urls.test.ts
index 3409e83c5b..caf5754f38 100644
--- a/src/editors/data/services/cms/urls.test.ts
+++ b/src/editors/data/services/cms/urls.test.ts
@@ -3,6 +3,7 @@ import {
   unit,
   libraryV1,
   block,
+  blockV1,
   blockAncestor,
   blockStudioView,
   courseAssets,
@@ -115,10 +116,20 @@ describe('cms url methods', () => {
         .toEqual(`${studioEndpointUrl}/api/xblock/v2/xblocks/${v2BlockId}/fields/`);
     });
   });
+  describe('blockV1', () => {
+    it('returns v1 REST url with studioEndpointUrl and blockId', () => {
+      expect(blockV1({ studioEndpointUrl, blockId }))
+        .toEqual(`${studioEndpointUrl}/api/contentstore/v1/xblock/${blockId}/`);
+    });
+    it('returns v2 url with studioEndpointUrl and v2BlockId', () => {
+      expect(blockV1({ studioEndpointUrl, blockId: v2BlockId }))
+        .toEqual(`${studioEndpointUrl}/api/xblock/v2/xblocks/${v2BlockId}/fields/`);
+    });
+  });
   describe('blockAncestor', () => {
     it('returns url with studioEndpointUrl, blockId and ancestor query', () => {
       expect(blockAncestor({ studioEndpointUrl, blockId }))
-        .toEqual(`${block({ studioEndpointUrl, blockId })}?fields=ancestorInfo`);
+        .toEqual(`${blockV1({ studioEndpointUrl, blockId })}?fields=ancestorInfo`);
     });
     it('throws error with studioEndpointUrl, v2 blockId and ancestor query', () => {
       expect(() => {
diff --git a/src/editors/data/services/cms/urls.ts b/src/editors/data/services/cms/urls.ts
index d24bd6bcc2..9ef361adf9 100644
--- a/src/editors/data/services/cms/urls.ts
+++ b/src/editors/data/services/cms/urls.ts
@@ -42,15 +42,28 @@ export const returnUrl = ({
   return '';
 };
 
+// Legacy Studio xblock detail base. Kept for the handler/view sub-routes
+// (`/studio_view`, `/handler/...`) that are NOT served by the v1 REST viewset
+// and are appended onto this URL by `blockStudioView` / `videoTranscripts`.
 export const block = (({ studioEndpointUrl, blockId }) => (
   blockId.startsWith('lb:')
     ? `${studioEndpointUrl}/api/xblock/v2/xblocks/${blockId}/fields/`
     : `${studioEndpointUrl}/xblock/${blockId}`
 )) satisfies UrlFunction;
 
+// FC-0118 (ADR 0028/0037): standardized v1 xblock REST detail URL, for CRUD
+// (retrieve/update/delete). The trailing slash is required by the DRF
+// DefaultRouter. `lb:` library blocks keep the v2 library xblock API.
+export const blockV1 = (({ studioEndpointUrl, blockId }) => (
+  blockId.startsWith('lb:')
+    ? `${studioEndpointUrl}/api/xblock/v2/xblocks/${blockId}/fields/`
+    : `${studioEndpointUrl}/api/contentstore/v1/xblock/${blockId}/`
+)) satisfies UrlFunction;
+
 export const blockAncestor = (({ studioEndpointUrl, blockId }) => {
   if (blockId.includes('block-v1')) {
-    return `${block({ studioEndpointUrl, blockId })}?fields=ancestorInfo`;
+    // v1 retrieve honours the legacy `?fields=ancestorInfo` pass-through.
+    return `${blockV1({ studioEndpointUrl, blockId })}?fields=ancestorInfo`;
   }
   throw new Error('Block ancestor not available (and not needed) for V2 blocks');
 }) satisfies UrlFunction;
diff --git a/src/editors/data/services/cms/utils.ts b/src/editors/data/services/cms/utils.ts
index 2e77435cd5..e06d37105a 100644
--- a/src/editors/data/services/cms/utils.ts
+++ b/src/editors/data/services/cms/utils.ts
@@ -23,6 +23,14 @@ export const post: Axios['post'] = (...args) => client().post(...args);
  */
 export const put: Axios['put'] = (...args) => client().put(...args);
 
+/**
+ * patch(url, data)
+ * simple wrapper providing an authenticated Http client patch action
+ * @param {string} url - target url
+ * @param {object|string} data - patch payload
+ */
+export const patch: Axios['patch'] = (...args) => client().patch(...args);
+
 /**
  * delete(url, data)
  * simple wrapper providing an authenticated Http client delete action