diff --git a/modules/sdk-core/src/bitgo/pendingApproval/pendingApproval.ts b/modules/sdk-core/src/bitgo/pendingApproval/pendingApproval.ts
index 5ca48252d4..822ef5bab4 100644
--- a/modules/sdk-core/src/bitgo/pendingApproval/pendingApproval.ts
+++ b/modules/sdk-core/src/bitgo/pendingApproval/pendingApproval.ts
@@ -31,6 +31,8 @@ type PreApproveResult = {
   halfSigned?: string;
 };
 
+// TODO(WCN-541): add optional attestation pass-through for PUT /pendingapprovals/:id (deferred
+// until multisig attestation, WCN-539, is verified end-to-end on staging).
 type ApprovePendingApprovalRequestBody = {
   state: 'approved';
   otp: string | undefined;
diff --git a/modules/sdk-core/src/bitgo/tss/common.ts b/modules/sdk-core/src/bitgo/tss/common.ts
index 7903038740..83ec34bad7 100644
--- a/modules/sdk-core/src/bitgo/tss/common.ts
+++ b/modules/sdk-core/src/bitgo/tss/common.ts
@@ -111,6 +111,8 @@ export async function sendSignatureShare(
   const urlPath = '/wallet/' + walletId + '/txrequests/' + txRequestId + addendum + '/signatureshares';
   const reqTracer = reqId || new RequestTracer();
   bitgo.setRequestTracer(reqTracer);
+  // TODO(WCN-541): add optional attestation pass-through for MPC /signatureshares, first round
+  // only (deferred until multisig attestation, WCN-539, is verified end-to-end on staging).
   return bitgo
     .post(bitgo.url(urlPath, 2))
     .send({
diff --git a/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts b/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
index 2b983ccdd7..1d830a3ede 100644
--- a/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
+++ b/modules/sdk-core/src/bitgo/utils/tss/baseTSSUtils.ts
@@ -514,6 +514,8 @@ export default class BaseTssUtils<KeyShare> extends MpcUtils implements ITssUtil
     preview?: boolean,
     reqId?: IRequestTracer
   ): Promise<TxRequest> {
+    // TODO(WCN-541): add optional attestation pass-through for MPC /txrequests (deferred until
+    // multisig attestation, WCN-539, is verified end-to-end on staging).
     const whitelistedParams = {
       intent: {
         ...intentOptions,
diff --git a/modules/sdk-core/src/bitgo/wallet/BuildParams.ts b/modules/sdk-core/src/bitgo/wallet/BuildParams.ts
index a635b2057b..cc748742a1 100644
--- a/modules/sdk-core/src/bitgo/wallet/BuildParams.ts
+++ b/modules/sdk-core/src/bitgo/wallet/BuildParams.ts
@@ -64,6 +64,23 @@ export const BuildParamsOffchain = t.partial({
   idfUserId: t.unknown,
 });
 
+/**
+ * WebAuthn attestation proving a passkey user signed off on this withdrawal intent.
+ * Pure pass-through — the SDK does not validate or interpret this payload.
+ *
+ * TODO(WCN-541): move this codec to @bitgo/public-types as the shared AttestationPayload
+ * and add it to the canonical TxSendBody/BuildParams codecs there; this local copy only
+ * covers the multisig /tx/build, /tx/send, and /tx/initiate paths.
+ */
+export const AttestationPayload = t.type({
+  signature: t.string,
+  credentialId: t.string,
+  clientDataJSON: t.string,
+  authenticatorData: t.string,
+});
+
+export type AttestationPayload = t.TypeOf<typeof AttestationPayload>;
+
 export const BuildParams = t.exact(
   t.intersection([
     BuildParamsUTXO,
@@ -135,6 +152,8 @@ export const BuildParams = t.exact(
       feeToken: t.unknown,
       // Bridging parameters for cross-chain operations (e.g., BTC to sBTC)
       bridgingParams: t.unknown,
+      // WebAuthn attestation for the withdrawal intent (WCN-539) — pass-through only.
+      attestation: AttestationPayload,
     }),
   ])
 );
diff --git a/modules/sdk-core/src/bitgo/wallet/iWallet.ts b/modules/sdk-core/src/bitgo/wallet/iWallet.ts
index a9663e6bbc..067660bcb6 100644
--- a/modules/sdk-core/src/bitgo/wallet/iWallet.ts
+++ b/modules/sdk-core/src/bitgo/wallet/iWallet.ts
@@ -38,6 +38,7 @@ import {
   TxRequest,
 } from '../utils';
 import { SerializedNtilde } from '../../account-lib/mpc/tss/ecdsa/types';
+import { AttestationPayload } from './BuildParams';
 import { IAddressBook } from '../address-book';
 import { WalletUser, AddressQueryResult } from '@bitgo/public-types';
 import { SubmitTransactionResponse } from '../inscriptionBuilder';
@@ -203,6 +204,8 @@ export interface PrebuildTransactionOptions {
   idfUserId?: string;
   idfVersion?: number;
   comment?: string;
+  /** WebAuthn attestation for the withdrawal intent (WCN-539) — pass-through only. */
+  attestation?: AttestationPayload;
   [index: string]: unknown;
   tokenName?: string;
   nftCollectionId?: string;
@@ -883,6 +886,8 @@ export interface SubmitTransactionOptions {
   };
   comment?: string;
   txRequestId?: string;
+  /** WebAuthn attestation for the withdrawal intent (WCN-539) — pass-through only. */
+  attestation?: AttestationPayload;
 }
 
 export interface SendOptions {
diff --git a/modules/sdk-core/src/bitgo/wallet/wallet.ts b/modules/sdk-core/src/bitgo/wallet/wallet.ts
index a8c1952cf5..983c9d20c2 100644
--- a/modules/sdk-core/src/bitgo/wallet/wallet.ts
+++ b/modules/sdk-core/src/bitgo/wallet/wallet.ts
@@ -56,7 +56,7 @@ import { txParamsFromIntent } from '../utils/tss/baseTSSUtils';
 import { EcdsaMPCv2Utils, EcdsaUtils } from '../utils/tss/ecdsa';
 import EddsaUtils, { EddsaMPCv2Utils } from '../utils/tss/eddsa';
 import { getTxRequestApiVersion, validateTxRequestApiVersion } from '../utils/txRequest';
-import { buildParamKeys, BuildParams } from './BuildParams';
+import { buildParamKeys, BuildParams, AttestationPayload } from './BuildParams';
 import {
   AccelerateTransactionOptions,
   AddressesByBalanceOptions,
@@ -143,7 +143,9 @@ const debug = require('debug')('bitgo:v2:wallet');
 
 type ManageUnspents = 'consolidate' | 'fanout';
 
-const whitelistedSendParams = TxSendBody.type.types.flatMap((t) => Object.keys(t.props));
+// TODO(WCN-541): 'attestation' is appended locally because @bitgo/public-types' TxSendBody
+// codec doesn't declare it yet. Once TxSendBody adds it upstream, drop this local addition.
+const whitelistedSendParams = [...TxSendBody.type.types.flatMap((t) => Object.keys(t.props)), 'attestation'];
 
 export enum ManageUnspentsOptions {
   BUILD_ONLY,
@@ -5064,10 +5066,13 @@ export class Wallet implements IWallet {
     const whitelistedParams = this.baseCoin.preprocessBuildParams(_.pick(params, whitelistedSendParams));
     const reqTracer = reqId || new RequestTracer();
     this.bitgo.setRequestTracer(reqTracer);
+    // TODO(WCN-541): attestation is added to this local intersection because @bitgo/public-types'
+    // TxSendBody codec (t.exact) doesn't declare it yet, and t.exact strips undeclared keys on
+    // encode. Once TxSendBody adds it upstream, drop `attestation` from this local partial.
     return postWithCodec(
       this.bitgo,
       this.baseCoin.url('/wallet/' + this.id() + '/tx/send'),
-      t.intersection([TxSendBody, t.partial({ locktime: t.number })]),
+      t.intersection([TxSendBody, t.partial({ locktime: t.number, attestation: AttestationPayload })]),
       whitelistedParams
     ).result();
   }
@@ -5079,10 +5084,11 @@ export class Wallet implements IWallet {
     const whitelistedParams = this.baseCoin.preprocessBuildParams(_.pick(params, whitelistedSendParams));
     const reqTracer = reqId || new RequestTracer();
     this.bitgo.setRequestTracer(reqTracer);
+    // TODO(WCN-541): see sendTransaction — same local-codec workaround for attestation pass-through.
     return postWithCodec(
       this.bitgo,
       this.baseCoin.url('/wallet/' + this.id() + '/tx/initiate'),
-      TxSendBody,
+      t.intersection([TxSendBody, t.partial({ attestation: AttestationPayload })]),
       whitelistedParams
     ).result();
   }
diff --git a/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts b/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
index e88da25a62..e1f619b3ba 100644
--- a/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
+++ b/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
@@ -1,5 +1,5 @@
 import * as assert from 'assert';
-import { BuildParams } from '../../../../src/bitgo/wallet/BuildParams';
+import { BuildParams, buildParamKeys, AttestationPayload } from '../../../../src/bitgo/wallet/BuildParams';
 
 describe('BuildParams', function () {
   it('enforces codec', function () {
@@ -74,4 +74,36 @@ describe('BuildParams', function () {
       }
     );
   });
+
+  it('should whitelist attestation (WCN-539) while stripping unrelated unknown params', function () {
+    const attestation = {
+      signature: 'sig',
+      credentialId: 'cred-id',
+      clientDataJSON: 'client-data',
+      authenticatorData: 'auth-data',
+    };
+    assert.deepStrictEqual(
+      BuildParams.encode({
+        recipients: [{ amount: '10000', address: '2N9Ego9KidiZR8tMP82g6RaggQtcbR9zNzH' }],
+        attestation,
+        unknownField: 'should be stripped',
+      } as any),
+      {
+        recipients: [{ amount: '10000', address: '2N9Ego9KidiZR8tMP82g6RaggQtcbR9zNzH' }],
+        attestation,
+      }
+    );
+    assert.ok(buildParamKeys.includes('attestation'), 'buildParamKeys must include attestation');
+  });
+
+  it('AttestationPayload codec requires all four fields', function () {
+    const valid = {
+      signature: 'sig',
+      credentialId: 'cred-id',
+      clientDataJSON: 'client-data',
+      authenticatorData: 'auth-data',
+    };
+    assert.strictEqual(AttestationPayload.is(valid), true);
+    assert.strictEqual(AttestationPayload.is({ ...valid, signature: undefined }), false);
+  });
 });
diff --git a/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts b/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
index c1030ff859..de94f275b1 100644
--- a/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
+++ b/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
@@ -1,5 +1,7 @@
 import * as assert from 'assert';
+import * as t from 'io-ts';
 import { TxSendBody } from '@bitgo/public-types';
+import { AttestationPayload } from '../../../../src/bitgo/wallet/BuildParams';
 
 describe('SendTransactionRequest', function () {
   it('enforces codec', function () {
@@ -24,4 +26,31 @@ describe('SendTransactionRequest', function () {
       addressType: 'p2sh',
     });
   });
+
+  it('TxSendBody alone drops attestation (upstream codec has no such field yet — TODO(WCN-541))', function () {
+    assert.deepStrictEqual(
+      TxSendBody.encode({
+        txHex: '00',
+        attestation: { signature: 'sig', credentialId: 'c', clientDataJSON: 'cd', authenticatorData: 'ad' },
+      } as any),
+      { txHex: '00' }
+    );
+  });
+
+  it('the local intersection used by wallet.sendTransaction/initiateTransaction preserves attestation', function () {
+    // Mirrors the codec built inline in Wallet#sendTransaction/#initiateTransaction (WCN-539):
+    // TxSendBody is `t.exact` and strips unknown keys, so attestation is re-added via a sibling
+    // t.partial in the same intersection until @bitgo/public-types declares it upstream.
+    //
+    // Note: by the time this codec runs, the caller has already done
+    // `_.pick(params, whitelistedSendParams)`, so the object passed to `.encode()` never carries
+    // arbitrary unknown keys in production — this test reflects that, not raw request bodies.
+    const attestation = { signature: 'sig', credentialId: 'c', clientDataJSON: 'cd', authenticatorData: 'ad' };
+    const sendBodyWithAttestation = t.intersection([TxSendBody, t.partial({ attestation: AttestationPayload })]);
+
+    assert.deepStrictEqual(sendBodyWithAttestation.encode({ txHex: '00', attestation } as any), {
+      txHex: '00',
+      attestation,
+    });
+  });
 });