BitGo · abhi-bitgo · Aug 11, 2026
@@ -1572,6 +1572,83 @@ describe('V2 Wallet:', function () {
     });
   });
 
+  describe('Custody sBTC bridging/withdraw params pass-through', function () {
+    const bridgingParams = {
+      sbtc: {
+        amount: 100000,
+        stacksRecipient: 'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7',
+        maxFee: 5000,
+        lockTime: 144,
+      },
+    };
+    const sbtcWithdrawParams = {
+      amount: '100000',
+      btcAddress: '2N9Ego9KidiZR8tMP82g6RaggQtcbR9zNzH',
+      maxFee: '5000',
+    };
+
+    afterEach(function () {
+      nock.cleanAll();
+    });
+
+    it('should pass bridgingParams through sendMany to tx/initiate for custodial wallets', async function () {
+      const custodialWallet = new Wallet(bitgo, bitgo.coin('tbtc'), {
+        id: '5b34252f1bf349930e34020a',
+        coin: 'tbtc',
+        type: 'custodial',
+        keys: ['5b3424f91bf349930e340175'],
+      });
+
+      const initiatePath = `/api/v2/${custodialWallet.coin()}/wallet/${custodialWallet.id()}/tx/initiate`;
+      const response = nock(bgUrl)
+        .post(initiatePath, _.matches({ type: 'bridging', bridgingParams }))
+        .reply(200, { status: 'accepted', txRequestId: 'mock-tx-request-id' });
+
+      const result = await custodialWallet.sendMany({ type: 'bridging', bridgingParams });
+      response.isDone().should.be.true();
+      (result as any).status.should.equal('accepted');
+    });
+
+    it('should pass sbtcWithdrawParams through sendMany to tx/initiate for custodial wallets', async function () {
+      const custodialWallet = new Wallet(bitgo, bitgo.coin('tbtc'), {
+        id: '5b34252f1bf349930e34020a',
+        coin: 'tbtc',
+        type: 'custodial',
+        keys: ['5b3424f91bf349930e340175'],
+      });
+
+      const initiatePath = `/api/v2/${custodialWallet.coin()}/wallet/${custodialWallet.id()}/tx/initiate`;
+      const response = nock(bgUrl)
+        .post(initiatePath, _.matches({ sbtcWithdrawParams }))
+        .reply(200, { status: 'accepted', txRequestId: 'mock-tx-request-id' });
+
+      const result = await custodialWallet.sendMany({ sbtcWithdrawParams } as any);
+      response.isDone().should.be.true();
+      (result as any).status.should.equal('accepted');
+    });
+
+    it('should not forward bridgingParams/sbtcWithdrawParams to tx/send for non-custodial wallets', async function () {
+      const hotWallet = new Wallet(bitgo, bitgo.coin('tbtc'), {
+        id: '5b34252f1bf349930e34020a',
+        coin: 'tbtc',
+        keys: ['5b3424f91bf349930e340175'],
+      });
+
+      const prebuildAndSignStub = sinon
+        .stub(hotWallet, 'prebuildAndSignTransaction')
+        .resolves({ txHex: 'deadbeef' } as any);
+
+      const sendPath = `/api/v2/${hotWallet.coin()}/wallet/${hotWallet.id()}/tx/send`;
+      const response = nock(bgUrl)
+        .post(sendPath, (body) => !('bridgingParams' in body) && !('sbtcWithdrawParams' in body))
+        .reply(200, { status: 'accepted' });
+
+      await hotWallet.sendMany({ type: 'bridging', bridgingParams, sbtcWithdrawParams } as any);
+      response.isDone().should.be.true();
+      prebuildAndSignStub.restore();
+    });
+  });
+
   describe('Transaction prebuilds', function () {
     let ethWallet;
 

@@ -58,6 +58,19 @@ export const BuildParamsSbtc = t.partial({
   sbtcDepositParams: t.unknown,
 });
 
+/** Parameters for sBTC bridging (BTC to sBTC). Mirrors iWallet.ts's SbtcBridgingParams. */
+export const SbtcBridgingParams = t.type({
+  amount: t.union([t.number, t.string]),
+  stacksRecipient: t.string,
+  maxFee: t.union([t.number, t.string]),
+  lockTime: t.number,
+});
+
+/** Parameters for cross-chain bridging transactions. Mirrors iWallet.ts's BridgingParams. */
+export const BridgingParams = t.partial({
+  sbtc: SbtcBridgingParams,
+});
+
 export const BuildParamsOffchain = t.partial({
   idfSignedTimestamp: t.unknown,
   idfVersion: t.unknown,

@@ -57,7 +57,7 @@ import { postWithCodec } from '../utils/postWithCodec';
 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, SbtcWithdrawParams, BridgingParams } from './BuildParams';
 import {
   AccelerateTransactionOptions,
   AddressesByBalanceOptions,
@@ -148,6 +148,15 @@ type ManageUnspents = 'consolidate' | 'fanout';
 
 const whitelistedSendParams = TxSendBody.type.types.flatMap((t) => Object.keys(t.props));
 
+// 'bridgingParams' and 'sbtcWithdrawParams' are appended locally (scoped to /tx/initiate only)
+// because @bitgo/public-types' TxSendBody codec doesn't declare them yet. Custody (custodial,
+// non-TSS) sBTC mint/burn goes through sendMany -> initiateTransaction -> POST /tx/initiate,
+// which builds and signs server-side; without this, the fields would be picked off params but
+// then encoded away by TxSendBody's t.exact. Drop this local addition once TxSendBody adds the
+// fields upstream. Not added to whitelistedSendParams itself, since sendTransaction (/tx/send)
+// is for already-built/signed transactions and should not forward these build-time-only fields.
+const whitelistedInitiateParams = [...whitelistedSendParams, 'bridgingParams', 'sbtcWithdrawParams'];
+
 export enum ManageUnspentsOptions {
   BUILD_ONLY,
   BUILD_SIGN_SEND,
@@ -5339,13 +5348,19 @@ export class Wallet implements IWallet {
     // extract the whitelisted params from the top level, in case
     // other invalid params are present that would fail encoding
     // and fall back to the body params
-    const whitelistedParams = this.baseCoin.preprocessBuildParams(_.pick(params, whitelistedSendParams));
+    const whitelistedParams = this.baseCoin.preprocessBuildParams(_.pick(params, whitelistedInitiateParams));
     const reqTracer = reqId || new RequestTracer();
     this.bitgo.setRequestTracer(reqTracer);
+    // bridgingParams/sbtcWithdrawParams are added to this local intersection because
+    // @bitgo/public-types' TxSendBody codec (t.exact) doesn't declare them yet, and t.exact
+    // reconstructs the encoded body from only its declared props — dropping anything else.
     return postWithCodec(
       this.bitgo,
       this.baseCoin.url('/wallet/' + this.id() + '/tx/initiate'),
-      TxSendBody,
+      t.intersection([
+        TxSendBody,
+        t.partial({ bridgingParams: BridgingParams, sbtcWithdrawParams: SbtcWithdrawParams }),
+      ]),
       whitelistedParams
     ).result();
   }

@@ -1,5 +1,12 @@
 import * as assert from 'assert';
-import { BuildParams, buildParamKeys, AttestationPayload } from '../../../../src/bitgo/wallet/BuildParams';
+import {
+  BuildParams,
+  buildParamKeys,
+  AttestationPayload,
+  BridgingParams,
+  SbtcBridgingParams,
+  SbtcWithdrawParams,
+} from '../../../../src/bitgo/wallet/BuildParams';
 
 describe('BuildParams', function () {
   it('enforces codec', function () {
@@ -106,4 +113,37 @@ describe('BuildParams', function () {
     assert.strictEqual(AttestationPayload.is(valid), true);
     assert.strictEqual(AttestationPayload.is({ ...valid, signature: undefined }), false);
   });
+
+  it('SbtcBridgingParams codec requires all four fields', function () {
+    const valid = {
+      amount: 100000,
+      stacksRecipient: 'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7',
+      maxFee: 5000,
+      lockTime: 144,
+    };
+    assert.strictEqual(SbtcBridgingParams.is(valid), true);
+    assert.strictEqual(SbtcBridgingParams.is({ ...valid, amount: undefined }), false);
+    // amount/maxFee accept string or number, per iWallet.ts's SbtcBridgingParams
+    assert.strictEqual(SbtcBridgingParams.is({ ...valid, amount: '100000', maxFee: '5000' }), true);
+  });
+
+  it('BridgingParams codec validates the nested sbtc shape', function () {
+    const valid = {
+      sbtc: {
+        amount: 100000,
+        stacksRecipient: 'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7',
+        maxFee: 5000,
+        lockTime: 144,
+      },
+    };
+    assert.strictEqual(BridgingParams.is(valid), true);
+    assert.strictEqual(BridgingParams.is({}), true); // sbtc is optional
+    assert.strictEqual(BridgingParams.is({ sbtc: { amount: 100000 } }), false); // incomplete nested shape
+  });
+
+  it('SbtcWithdrawParams codec accepts partial string fields', function () {
+    assert.strictEqual(SbtcWithdrawParams.is({ amount: '100000', btcAddress: 'mtbtcaddr', maxFee: '5000' }), true);
+    assert.strictEqual(SbtcWithdrawParams.is({}), true);
+    assert.strictEqual(SbtcWithdrawParams.is({ amount: 100000 }), false); // must be string, not number
+  });
 });