diff --git a/modules/bitgo/test/v2/unit/wallet.ts b/modules/bitgo/test/v2/unit/wallet.ts
index 81013ade88..591ec1d38d 100644
--- a/modules/bitgo/test/v2/unit/wallet.ts
+++ b/modules/bitgo/test/v2/unit/wallet.ts
@@ -1572,6 +1572,62 @@ 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');
+    });
+  });
+
   describe('Transaction prebuilds', function () {
     let ethWallet;
 
diff --git a/modules/sdk-core/package.json b/modules/sdk-core/package.json
index d23c5c1fff..a30d01b043 100644
--- a/modules/sdk-core/package.json
+++ b/modules/sdk-core/package.json
@@ -40,7 +40,7 @@
     ]
   },
   "dependencies": {
-    "@bitgo/public-types": "6.53.0",
+    "@bitgo/public-types": "6.56.0",
     "@bitgo/sdk-lib-mpc": "^10.15.0",
     "@bitgo/secp256k1": "^1.11.0",
     "@bitgo/sjcl": "^1.1.0",
diff --git a/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts b/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
index e1f619b3ba..7390c1a6e0 100644
--- a/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
+++ b/modules/sdk-core/test/unit/bitgo/wallet/BuildParams.ts
@@ -1,5 +1,10 @@
 import * as assert from 'assert';
-import { BuildParams, buildParamKeys, AttestationPayload } from '../../../../src/bitgo/wallet/BuildParams';
+import {
+  BuildParams,
+  buildParamKeys,
+  AttestationPayload,
+  SbtcWithdrawParams,
+} from '../../../../src/bitgo/wallet/BuildParams';
 
 describe('BuildParams', function () {
   it('enforces codec', function () {
@@ -106,4 +111,10 @@ describe('BuildParams', function () {
     assert.strictEqual(AttestationPayload.is(valid), true);
     assert.strictEqual(AttestationPayload.is({ ...valid, signature: undefined }), false);
   });
+
+  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
+  });
 });
diff --git a/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts b/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
index 12e3b09906..bd8c343cd3 100644
--- a/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
+++ b/modules/sdk-core/test/unit/bitgo/wallet/SendTransactionRequest.ts
@@ -33,4 +33,64 @@ describe('SendTransactionRequest', function () {
       attestation,
     });
   });
+
+  it('preserves bridgingParams (CSHLD-1456: @bitgo/public-types TxSendBody declares it natively)', function () {
+    const bridgingParams = {
+      sbtc: {
+        amount: '100000',
+        stacksRecipient: 'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7',
+        maxFee: '5000',
+        lockTime: 144,
+      },
+    };
+
+    assert.deepStrictEqual(TxSendBody.encode({ txHex: '00', bridgingParams } as any), {
+      txHex: '00',
+      bridgingParams,
+    });
+  });
+
+  it('preserves sbtcWithdrawParams (CSHLD-1456: @bitgo/public-types TxSendBody declares it natively)', function () {
+    const sbtcWithdrawParams = { amount: '100000', btcAddress: 'mtbtcaddr', maxFee: '5000' };
+
+    assert.deepStrictEqual(TxSendBody.encode({ txHex: '00', sbtcWithdrawParams } as any), {
+      txHex: '00',
+      sbtcWithdrawParams,
+    });
+  });
+
+  it('validates bridgingParams.sbtc as a complete shape', function () {
+    const valid = {
+      sbtc: {
+        amount: '100000',
+        stacksRecipient: 'SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7',
+        maxFee: '5000',
+        lockTime: 144,
+      },
+    };
+    assert.strictEqual(TxSendBody.is({ bridgingParams: valid }), true);
+    assert.strictEqual(TxSendBody.is({}), true); // bridgingParams itself is optional
+    assert.strictEqual(TxSendBody.is({ bridgingParams: {} }), true); // sbtc is optional within bridgingParams
+
+    // amount/maxFee accept string or number
+    assert.strictEqual(
+      TxSendBody.is({ bridgingParams: { sbtc: { ...valid.sbtc, amount: 100000, maxFee: 5000 } } }),
+      true
+    );
+
+    // sbtc, once present, requires all four fields
+    const missingAmount = {
+      stacksRecipient: valid.sbtc.stacksRecipient,
+      maxFee: valid.sbtc.maxFee,
+      lockTime: valid.sbtc.lockTime,
+    };
+    assert.strictEqual(TxSendBody.is({ bridgingParams: { sbtc: missingAmount } }), false);
+  });
+
+  it('validates sbtcWithdrawParams fields as strings', function () {
+    const valid = { amount: '100000', btcAddress: 'mtbtcaddr', maxFee: '5000' };
+    assert.strictEqual(TxSendBody.is({ sbtcWithdrawParams: valid }), true);
+    assert.strictEqual(TxSendBody.is({ sbtcWithdrawParams: {} }), true); // all fields optional
+    assert.strictEqual(TxSendBody.is({ sbtcWithdrawParams: { ...valid, amount: 100000 } }), false); // must be string
+  });
 });
diff --git a/yarn.lock b/yarn.lock
index 5274dfc11c..ae55d5d6a8 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1043,10 +1043,10 @@
     monocle-ts "^2.3.13"
     newtype-ts "^0.3.5"
 
-"@bitgo/public-types@6.53.0":
-  version "6.53.0"
-  resolved "https://registry.npmjs.org/@bitgo/public-types/-/public-types-6.53.0.tgz#fedaf8dbdc7f5fbe25279e560fd76ed25d9443ed"
-  integrity sha512-nei+2f2fmrnqVZnQ2GBVSbHy0O5bZwcfp/R1jKpuYFOWQgeZtFmblVMhnbN1sfFVyAAGOdacZtx7d56+qZ0TNA==
+"@bitgo/public-types@6.56.0":
+  version "6.56.0"
+  resolved "https://registry.npmjs.org/@bitgo/public-types/-/public-types-6.56.0.tgz#ddfdb65273334a320dfa11de3f4ad48beba23ce0"
+  integrity sha512-IF+qN5gqVfkyBLC8e1K85fxOX4chbYNF1EWQZexqMJjVQZsijMe3m6qkQG8IBJPCH34yhHLa3WcV/sEXKoCT2g==
   dependencies:
     fp-ts "^2.0.0"
     io-ts "npm:@bitgo-forks/io-ts@2.1.4"