diff --git a/packages/upload-api/src/blob/accept.js b/packages/upload-api/src/blob/accept.js
index b41d5b857..fde33d0bb 100644
--- a/packages/upload-api/src/blob/accept.js
+++ b/packages/upload-api/src/blob/accept.js
@@ -1,5 +1,6 @@
 import * as Blob from '@storacha/capabilities/blob'
-import { Message, Invocation } from '@ucanto/core'
+import * as W3sBlob from '@storacha/capabilities/web3.storage/blob'
+import { Message, Receipt, Invocation } from '@ucanto/core'
 import * as Transport from '@ucanto/transport/car'
 import * as API from '../types.js'
 import * as HTTP from '@storacha/capabilities/http'
@@ -83,10 +84,34 @@ export const poll = async (context, receipt) => {
     configure.ok.connection
   )
 
+  // Create receipt for legacy `web3.storage/blob/accept`. The old client
+  // `@web3-storage/w3up-client` will poll for a receipt for this task, so
+  // we create one whose result is simply the result of the actual `blob/accept`
+  // task.
+  //
+  // TODO: remove when all users migrate to `@storacha/client`.
+  const w3sAccept = W3sBlob.accept.invoke({
+    issuer: context.id,
+    audience: context.id,
+    with: context.id.did(),
+    nb: {
+      blob: allocate.nb.blob,
+      space: /** @type {API.DIDKey} */ (DID.decode(allocate.nb.space).did()),
+      _put: { 'ucan/await': ['.out.ok', receipt.ran.link()] },
+    },
+  })
+  const w3sAcceptTask = await w3sAccept.delegate()
+  const w3sAcceptReceipt = await Receipt.issue({
+    issuer: context.id,
+    ran: w3sAcceptTask.cid,
+    result: acceptReceipt.out,
+    fx: acceptReceipt.fx,
+  })
+
   // record the invocation and the receipt
   const message = await Message.build({
     invocations: [configure.ok.invocation],
-    receipts: [acceptReceipt],
+    receipts: [acceptReceipt, w3sAcceptReceipt],
   })
   const messageWrite = await context.agentStore.messages.write({
     source: await Transport.outbound.encode(message),
diff --git a/packages/upload-api/src/blob/add.js b/packages/upload-api/src/blob/add.js
index 5dc3a2cd4..f37372c0c 100644
--- a/packages/upload-api/src/blob/add.js
+++ b/packages/upload-api/src/blob/add.js
@@ -4,6 +4,7 @@ import * as Transport from '@ucanto/transport/car'
 import { ed25519 } from '@ucanto/principal'
 import * as Blob from '@storacha/capabilities/blob'
 import * as SpaceBlob from '@storacha/capabilities/space/blob'
+import * as W3sBlob from '@storacha/capabilities/web3.storage/blob'
 import * as HTTP from '@storacha/capabilities/http'
 import * as Digest from 'multiformats/hashes/digest'
 import * as DID from '@ipld/dag-ucan/did'
@@ -50,6 +51,14 @@ export function blobAddProvider(context) {
         return allocation
       }
 
+      const allocationW3s = await allocateW3s({
+        context,
+        blob,
+        space,
+        cause: invocation.link(),
+        receipt: allocation.ok.receipt,
+      })
+
       const delivery = await put({
         blob,
         allocation: allocation.ok,
@@ -66,7 +75,16 @@ export function blobAddProvider(context) {
         return acceptance
       }
 
-      // Create a result describing the this invocation workflow
+      const acceptanceW3s = await acceptW3s({
+        context,
+        provider: allocation.ok.provider,
+        blob,
+        space,
+        delivery: delivery,
+        acceptance: acceptance.ok,
+      })
+
+      // Create a result describing this invocation workflow
       let result = Server.ok({
         /** @type {API.SpaceBlobAddSuccess['site']} */
         site: {
@@ -74,12 +92,20 @@ export function blobAddProvider(context) {
         },
       })
         .fork(allocation.ok.task)
+        .fork(allocationW3s.task)
         .fork(delivery.task)
         .fork(acceptance.ok.task)
+        .fork(acceptanceW3s.task)
 
       // As a temporary solution we fork all add effects that add inline
       // receipts so they can be delivered to the client.
-      const fx = [...allocation.ok.fx, ...delivery.fx, ...acceptance.ok.fx]
+      const fx = [
+        ...allocation.ok.fx,
+        ...allocationW3s.fx,
+        ...delivery.fx,
+        ...acceptance.ok.fx,
+        ...acceptanceW3s.fx,
+      ]
       for (const task of fx) {
         result = result.fork(task)
       }
@@ -172,6 +198,49 @@ async function allocate({ context, blob, space, cause }) {
   })
 }
 
+/**
+ * Create an allocation task and receipt using the legacy
+ * `web3.storage/blob/allocate` capability. This enables backwards compatibility
+ * with `@web3-storage/w3up-client`.
+ *
+ * TODO: remove when all users migrate to `@storacha/client`.
+ *
+ * @param {object} allocate
+ * @param {API.BlobServiceContext} allocate.context
+ * @param {API.BlobModel} allocate.blob
+ * @param {API.DIDKey} allocate.space
+ * @param {API.Link} allocate.cause
+ * @param {API.Receipt<API.BlobAllocateSuccess, API.BlobAcceptFailure>} allocate.receipt
+ */
+async function allocateW3s({ context, blob, space, cause, receipt }) {
+  const w3sAllocate = W3sBlob.allocate.invoke({
+    issuer: context.id,
+    audience: context.id,
+    with: context.id.did(),
+    nb: { blob, cause, space },
+    expiration: Infinity,
+  })
+  const w3sAllocateTask = await w3sAllocate.delegate()
+
+  const w3sAllocateReceipt = await Receipt.issue({
+    issuer: context.id,
+    ran: w3sAllocateTask.cid,
+    result: receipt.out,
+  })
+
+  const w3sAllocateConclude = createConcludeInvocation(
+    context.id,
+    context.id,
+    w3sAllocateReceipt
+  )
+
+  return {
+    task: w3sAllocateTask,
+    receipt: w3sAllocateReceipt,
+    fx: [await w3sAllocateConclude.delegate()],
+  }
+}
+
 /**
  * Create put task and check if there is a receipt for it already.
  * A `http/put` should be task is stored by the service, if it does not exist
@@ -313,3 +382,66 @@ async function accept({ context, provider, blob, space, delivery }) {
     fx: receipt ? [await conclude(receipt, context.id)] : [],
   })
 }
+
+/**
+ * Create an accept task and receipt using the legacy
+ * `web3.storage/blob/accept` capability. This enables backwards compatibility
+ * with `@web3-storage/w3up-client`.
+ *
+ * TODO: remove when all users migrate to `@storacha/client`.
+ *
+ * @param {object} input
+ * @param {API.BlobServiceContext} input.context
+ * @param {API.Principal} input.provider
+ * @param {API.BlobModel} input.blob
+ * @param {API.DIDKey} input.space
+ * @param {object} input.delivery
+ * @param {API.Invocation<API.HTTPPut>} input.delivery.task
+ * @param {API.Receipt|null} input.delivery.receipt
+ * @param {object} input.acceptance
+ * @param {API.Receipt|null} input.acceptance.receipt
+ */
+async function acceptW3s({ context, blob, space, delivery, acceptance }) {
+  // 1. Create web3.storage/blob/accept invocation and task
+  const w3sAccept = W3sBlob.accept.invoke({
+    issuer: context.id,
+    audience: context.id,
+    with: context.id.did(),
+    nb: {
+      blob,
+      space,
+      _put: { 'ucan/await': ['.out.ok', delivery.task.link()] },
+    },
+  })
+  const w3sAcceptTask = await w3sAccept.delegate()
+
+  let w3sAcceptReceipt = null
+  // If put has failed, we propagate the error to the `blob/accept` receipt.
+  if (delivery.receipt?.out.error) {
+    w3sAcceptReceipt = await Receipt.issue({
+      issuer: context.id,
+      ran: w3sAcceptTask,
+      result: {
+        error: new AwaitError({
+          cause: delivery.receipt.out.error,
+          at: '.out.ok',
+          reference: delivery.task.link(),
+        }),
+      },
+    })
+  }
+  // If `blob/accept` receipt is present, we issue a receipt for
+  // `web3.storage/blob/accept`.
+  else if (acceptance.receipt) {
+    w3sAcceptReceipt = await Receipt.issue({
+      issuer: context.id,
+      ran: w3sAcceptTask,
+      result: acceptance.receipt.out,
+    })
+  }
+
+  return {
+    task: w3sAcceptTask,
+    fx: w3sAcceptReceipt ? [await conclude(w3sAcceptReceipt, context.id)] : [],
+  }
+}
diff --git a/packages/upload-api/src/types.ts b/packages/upload-api/src/types.ts
index 18101f195..fba81866b 100644
--- a/packages/upload-api/src/types.ts
+++ b/packages/upload-api/src/types.ts
@@ -414,6 +414,8 @@ export interface RevocationServiceContext {
 }
 
 export interface ConcludeServiceContext {
+  /** Upload service signer. */
+  id: Signer
   /**
    * Store for invocations & receipts.
    */
diff --git a/packages/upload-api/test/handlers/blob.js b/packages/upload-api/test/handlers/blob.js
index 3a491f49b..f0ecb1b4a 100644
--- a/packages/upload-api/test/handlers/blob.js
+++ b/packages/upload-api/test/handlers/blob.js
@@ -56,7 +56,7 @@ export const test = {
         blobAdd.out.ok.site['ucan/await'][1],
         next.accept.task.cid
       )
-      assert.equal(blobAdd.fx.fork.length, 4)
+      assert.equal(blobAdd.fx.fork.length, 7)
 
       // validate receipt next
       assert.ok(next.allocate.task)
diff --git a/packages/upload-client/src/blob/add.js b/packages/upload-client/src/blob/add.js
index 0f4793767..621cbfc7e 100644
--- a/packages/upload-client/src/blob/add.js
+++ b/packages/upload-client/src/blob/add.js
@@ -1,5 +1,4 @@
 import { ed25519 } from '@ucanto/principal'
-import { conclude } from '@storacha/capabilities/ucan'
 import * as UCAN from '@storacha/capabilities/ucan'
 import { Delegation, Receipt } from '@ucanto/core'
 import * as BlobCapabilities from '@storacha/capabilities/blob'
@@ -121,7 +120,7 @@ export function createConcludeInvocation(id, serviceDid, receipt) {
     receiptBlocks.push(block)
     receiptCids.push(block.cid)
   }
-  const concludeAllocatefx = conclude.invoke({
+  const concludeAllocatefx = UCAN.conclude.invoke({
     issuer: id,
     audience: serviceDid,
     with: id.toDIDKey(),
@@ -292,9 +291,12 @@ export async function add(
     )
     const ucanConclude = await httpPutConcludeInvocation.execute(conn)
     if (!ucanConclude.out.ok) {
-      throw new Error(`failed ${SpaceBlobCapabilities.add.can} invocation`, {
-        cause: result.out.error,
-      })
+      throw new Error(
+        `failed ${UCAN.conclude.can} for ${HTTPCapabilities.put.can} invocation`,
+        {
+          cause: result.out.error,
+        }
+      )
     }
   }
 
diff --git a/packages/upload-client/test/blob.test.js b/packages/upload-client/test/blob.test.js
index 48d66a4cc..dc9ed386a 100644
--- a/packages/upload-client/test/blob.test.js
+++ b/packages/upload-client/test/blob.test.js
@@ -185,7 +185,7 @@ describe('Blob.add', () => {
         { connection }
       ),
       {
-        message: 'failed space/blob/add invocation',
+        message: 'failed ucan/conclude for http/put invocation',
       }
     )
   })
diff --git a/packages/w3up-client/package.json b/packages/w3up-client/package.json
index ecc5a3eb8..040224a4b 100644
--- a/packages/w3up-client/package.json
+++ b/packages/w3up-client/package.json
@@ -158,8 +158,10 @@
     "@types/mocha": "^10.0.1",
     "@types/node": "^20.8.4",
     "@ucanto/server": "^10.0.0",
+    "@web3-storage/access": "^20.1.0",
     "@web3-storage/content-claims": "^4.0.4",
     "@web3-storage/data-segment": "^5.0.0",
+    "@web3-storage/w3up-client": "^16.5.1",
     "assert": "^2.0.0",
     "c8": "^7.13.0",
     "hundreds": "^0.0.9",
diff --git a/packages/w3up-client/test/legacy-compat.node.test.js b/packages/w3up-client/test/legacy-compat.node.test.js
new file mode 100644
index 000000000..43a4851e8
--- /dev/null
+++ b/packages/w3up-client/test/legacy-compat.node.test.js
@@ -0,0 +1,69 @@
+import http from 'node:http'
+import { Client } from '@web3-storage/w3up-client'
+import { AgentData } from '@web3-storage/access'
+import * as Link from 'multiformats/link'
+import { Message } from '@ucanto/core'
+import * as CAR from '@ucanto/transport/car'
+import * as Test from './test.js'
+import { randomBytes } from './helpers/random.js'
+
+/** @param {import('@storacha/upload-api').AgentStore} agentStore */
+const createReceiptsServer = (agentStore) =>
+  http.createServer(async (req, res) => {
+    const task = Link.parse(req.url?.split('/').pop() ?? '')
+    const receiptGet = await agentStore.receipts.get(task)
+    if (receiptGet.error) {
+      res.writeHead(404)
+      return res.end()
+    }
+    const message = await Message.build({ receipts: [receiptGet.ok] })
+    const request = CAR.request.encode(message)
+    res.writeHead(200)
+    res.end(request.body)
+  })
+
+/** @type {Test.Suite} */
+export const testLegacyCompatibility = {
+  uploadFile: Test.withContext({
+    'should upload a file to the service via legacy client': async (
+      assert,
+      { connection, provisionsStorage, agentStore }
+    ) => {
+      const receiptsServer = createReceiptsServer(agentStore)
+      const receiptsEndpoint = await new Promise((resolve) => {
+        receiptsServer.listen(() => {
+          // @ts-expect-error
+          resolve(new URL(`http://127.0.0.1:${receiptsServer.address().port}`))
+        })
+      })
+
+      try {
+        const bytes = await randomBytes(128)
+        const file = new Blob([bytes])
+        const alice = new Client(await AgentData.create(), {
+          // @ts-expect-error service no longer implements `store/*`
+          serviceConf: { access: connection, upload: connection },
+          receiptsEndpoint,
+        })
+
+        const space = await alice.createSpace('upload-test')
+        const auth = await space.createAuthorization(alice)
+        await alice.addSpace(auth)
+        await alice.setCurrentSpace(space.did())
+
+        await provisionsStorage.put({
+          // @ts-expect-error
+          provider: connection.id.did(),
+          account: alice.agent.did(),
+          consumer: space.did(),
+        })
+
+        await assert.doesNotReject(alice.uploadFile(file))
+      } finally {
+        receiptsServer.close()
+      }
+    },
+  }),
+}
+
+Test.test({ LegacyCompatibility: testLegacyCompatibility })
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 1280c8858..7a25e3278 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -780,12 +780,18 @@ importers:
       '@ucanto/server':
         specifier: ^10.0.0
         version: 10.0.0
+      '@web3-storage/access':
+        specifier: ^20.1.0
+        version: 20.1.0
       '@web3-storage/content-claims':
         specifier: ^4.0.4
         version: 4.0.5
       '@web3-storage/data-segment':
         specifier: ^5.0.0
         version: 5.3.0
+      '@web3-storage/w3up-client':
+        specifier: ^16.5.1
+        version: 16.5.1
       assert:
         specifier: ^2.0.0
         version: 2.1.0
@@ -2520,6 +2526,16 @@ packages:
   '@web-std/stream@1.0.0':
     resolution: {integrity: sha512-jyIbdVl+0ZJyKGTV0Ohb9E6UnxP+t7ZzX4Do3AHjZKxUXKMs9EmqnBDQgHF7bEw0EzbQygOjtt/7gvtmi//iCQ==}
 
+  '@web3-storage/access@20.1.0':
+    resolution: {integrity: sha512-IY6ICPRWE8++2jxvy+LzAiFvwAOIHR8cu9eNt+VT5sAFE796o4ma7GSU0eXRCiShmV2n6iSWAwWRT6XD5zIqPA==}
+
+  '@web3-storage/blob-index@1.0.4':
+    resolution: {integrity: sha512-04+PrmVHFT+xzRhyIPdcvGc8Y2NDffUe8R1gJOyErVzEVz5N1I9Q/BrlFHYt/A4HrjM5JBsxqSrZgTIkjfPmLA==}
+    engines: {node: '>=16.15'}
+
+  '@web3-storage/capabilities@17.4.1':
+    resolution: {integrity: sha512-GogLfON8PZabi03CUyncBvMcCi36yQ/0iR5P8kr4pxdnZm7OuAn4sEwbEB8rTKbah5V10Vwgb3O5dh0FBgyjHg==}
+
   '@web3-storage/content-claims@4.0.5':
     resolution: {integrity: sha512-+WpCkTN8aRfUCrCm0kOMZad+FRnFymVDFvS6/+PJMPGP17cci1/c5lqYdrjFV+5MkhL+BkUJVtRTx02G31FHmQ==}
 
@@ -2532,9 +2548,23 @@ packages:
   '@web3-storage/data-segment@5.3.0':
     resolution: {integrity: sha512-zFJ4m+pEKqtKatJNsFrk/2lHeFSbkXZ6KKXjBe7/2ayA9wAar7T/unewnOcZrrZTnCWmaxKsXWqdMFy9bXK9dw==}
 
+  '@web3-storage/did-mailto@2.1.0':
+    resolution: {integrity: sha512-TRmfSXj1IhtX3ESurSNOylZSBKi0z/VJNoMLpof+AVRdovgZjjocpiePQTs2pfHKqHTHfJXc9AboWyK4IKTWMw==}
+    engines: {node: '>=16.15'}
+
+  '@web3-storage/filecoin-client@3.3.4':
+    resolution: {integrity: sha512-T2xur1NPvuH09yajyjCWEl7MBH712nqHERj51w4nDp6f8libMCKY6lca0frCrm4OC5s8oy0ZtoRFhsRYxgTzSg==}
+
   '@web3-storage/sigv4@1.0.2':
     resolution: {integrity: sha512-ZUXKK10NmuQgPkqByhb1H3OQxkIM0CIn2BMPhGQw7vQw8WIzrBkk9IJiAVfJ/UVBFrf6uzPbx2lEBLt4diCMnQ==}
 
+  '@web3-storage/upload-client@17.1.0':
+    resolution: {integrity: sha512-0tUMe4Ez9gmUZjgn1Nrl6HYdGEsYyeLa6JrpoXcCGTQDBW2FehALc+GZZeoIjYQexRpw+qt9JstuJNN9dUNETw==}
+
+  '@web3-storage/w3up-client@16.5.1':
+    resolution: {integrity: sha512-tsBUSo6/bPElGAlMbHVeQDMgg4krRrKXOBl0TZttAAIYcMzTvm7fkDfD9+5rvJFsa/a846XqPoxtO21LwL768A==}
+    engines: {node: '>=18'}
+
   '@webassemblyjs/ast@1.14.1':
     resolution: {integrity: sha512-nuBEDgQfm1ccRp/8bCQrx1frohyufl4JlbMMZ4P1wpeOfDhF6FQkxZJ1b/e+PLwr6X1Nhw6OLme5usuBWYBvuQ==}
 
@@ -10168,6 +10198,48 @@ snapshots:
     dependencies:
       web-streams-polyfill: 3.3.3
 
+  '@web3-storage/access@20.1.0':
+    dependencies:
+      '@ipld/car': 5.3.3
+      '@ipld/dag-ucan': 3.4.0
+      '@scure/bip39': 1.4.0
+      '@storacha/one-webcrypto': 1.0.1
+      '@ucanto/client': 9.0.1
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@ucanto/principal': 9.0.1
+      '@ucanto/transport': 9.1.1
+      '@ucanto/validator': 9.0.2
+      '@web3-storage/capabilities': 17.4.1
+      '@web3-storage/did-mailto': 2.1.0
+      bigint-mod-arith: 3.3.1
+      conf: 11.0.2
+      multiformats: 12.1.3
+      p-defer: 4.0.1
+      type-fest: 4.26.1
+      uint8arrays: 4.0.10
+
+  '@web3-storage/blob-index@1.0.4':
+    dependencies:
+      '@ipld/dag-cbor': 9.2.2
+      '@storacha/one-webcrypto': 1.0.1
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@web3-storage/capabilities': 17.4.1
+      carstream: 2.2.0
+      multiformats: 13.3.1
+      uint8arrays: 5.1.0
+
+  '@web3-storage/capabilities@17.4.1':
+    dependencies:
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@ucanto/principal': 9.0.1
+      '@ucanto/transport': 9.1.1
+      '@ucanto/validator': 9.0.2
+      '@web3-storage/data-segment': 5.3.0
+      uint8arrays: 5.1.0
+
   '@web3-storage/content-claims@4.0.5':
     dependencies:
       '@ucanto/client': 9.0.1
@@ -10198,10 +10270,59 @@ snapshots:
       multiformats: 13.3.1
       sync-multihash-sha2: 1.0.0
 
+  '@web3-storage/did-mailto@2.1.0': {}
+
+  '@web3-storage/filecoin-client@3.3.4':
+    dependencies:
+      '@ipld/dag-ucan': 3.4.0
+      '@ucanto/client': 9.0.1
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@ucanto/transport': 9.1.1
+      '@web3-storage/capabilities': 17.4.1
+
   '@web3-storage/sigv4@1.0.2':
     dependencies:
       '@noble/hashes': 1.5.0
 
+  '@web3-storage/upload-client@17.1.0':
+    dependencies:
+      '@ipld/car': 5.3.3
+      '@ipld/dag-cbor': 9.2.2
+      '@ipld/dag-ucan': 3.4.0
+      '@ipld/unixfs': 2.2.0
+      '@ucanto/client': 9.0.1
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@ucanto/transport': 9.1.1
+      '@web3-storage/blob-index': 1.0.4
+      '@web3-storage/capabilities': 17.4.1
+      '@web3-storage/data-segment': 5.3.0
+      '@web3-storage/filecoin-client': 3.3.4
+      ipfs-utils: 9.0.14(encoding@0.1.13)
+      multiformats: 12.1.3
+      p-retry: 5.1.2
+      varint: 6.0.0
+    transitivePeerDependencies:
+      - encoding
+
+  '@web3-storage/w3up-client@16.5.1':
+    dependencies:
+      '@ipld/dag-ucan': 3.4.0
+      '@ucanto/client': 9.0.1
+      '@ucanto/core': 10.0.1
+      '@ucanto/interface': 10.0.1
+      '@ucanto/principal': 9.0.1
+      '@ucanto/transport': 9.1.1
+      '@web3-storage/access': 20.1.0
+      '@web3-storage/blob-index': 1.0.4
+      '@web3-storage/capabilities': 17.4.1
+      '@web3-storage/did-mailto': 2.1.0
+      '@web3-storage/filecoin-client': 3.3.4
+      '@web3-storage/upload-client': 17.1.0
+    transitivePeerDependencies:
+      - encoding
+
   '@webassemblyjs/ast@1.14.1':
     dependencies:
       '@webassemblyjs/helper-numbers': 1.13.2