diff --git a/modules/utxo-core/.mocharc.js b/modules/utxo-core/.mocharc.cjs
similarity index 66%
rename from modules/utxo-core/.mocharc.js
rename to modules/utxo-core/.mocharc.cjs
index 5fc6096dae..16b4a65116 100644
--- a/modules/utxo-core/.mocharc.js
+++ b/modules/utxo-core/.mocharc.cjs
@@ -1,6 +1,6 @@
 'use strict';
 
 module.exports = {
-  require: 'ts-node/register',
+  "node-option": ["import=tsx"],
   extension: ['.js', '.ts'],
 };
diff --git a/modules/utxo-core/package.json b/modules/utxo-core/package.json
index 682f42018c..f38d659e2b 100644
--- a/modules/utxo-core/package.json
+++ b/modules/utxo-core/package.json
@@ -27,7 +27,7 @@
     "lint": "eslint --quiet .",
     "prepare": "npm run build",
     "test": "npm run unit-test",
-    "unit-test": "mocha --recursive \"dist/test/**/*.js\""
+    "unit-test": "mocha --recursive test"
   },
   "author": "BitGo SDK Team <sdkteam@bitgo.com>",
   "license": "MIT",
@@ -45,7 +45,7 @@
   "publishConfig": {
     "access": "public"
   },
-  "type": "commonjs",
+  "type": "module",
   "nyc": {
     "extension": [
       ".ts"
@@ -58,5 +58,9 @@
     "bip174": "npm:@bitgo-forks/bip174@3.1.0-master.4",
     "bitcoinjs-message": "npm:@bitgo-forks/bitcoinjs-message@1.0.0-master.3"
   },
-  "gitHead": "18e460ddf02de2dbf13c2aa243478188fb539f0c"
+  "gitHead": "18e460ddf02de2dbf13c2aa243478188fb539f0c",
+  "devDependencies": {
+    "@types/node": "^24",
+    "tsx": "^4.20.3"
+  }
 }
diff --git a/modules/utxo-core/src/bip65/index.ts b/modules/utxo-core/src/bip65/index.ts
index 2ceffe5de4..788e899a27 100644
--- a/modules/utxo-core/src/bip65/index.ts
+++ b/modules/utxo-core/src/bip65/index.ts
@@ -1 +1 @@
-export * from './locktime';
+export * from './locktime.js';
diff --git a/modules/utxo-core/src/descriptor/Output.ts b/modules/utxo-core/src/descriptor/Output.ts
index 9d2f5b875f..1bf3b559a3 100644
--- a/modules/utxo-core/src/descriptor/Output.ts
+++ b/modules/utxo-core/src/descriptor/Output.ts
@@ -2,10 +2,10 @@ import assert from 'assert';
 
 import { Descriptor } from '@bitgo/wasm-miniscript';
 
-import { getFixedOutputSum, MaxOutput, Output, PrevOutput } from '../Output';
+import { getFixedOutputSum, MaxOutput, Output, PrevOutput } from '../Output.js';
 
-import { DescriptorMap } from './DescriptorMap';
-import { getDescriptorAtIndexCheckScript } from './derive';
+import { DescriptorMap } from './DescriptorMap.js';
+import { getDescriptorAtIndexCheckScript } from './derive.js';
 
 export type WithDescriptor<T> = T & {
   descriptor: Descriptor;
diff --git a/modules/utxo-core/src/descriptor/VirtualSize.ts b/modules/utxo-core/src/descriptor/VirtualSize.ts
index 01af5369a1..ead37dedce 100644
--- a/modules/utxo-core/src/descriptor/VirtualSize.ts
+++ b/modules/utxo-core/src/descriptor/VirtualSize.ts
@@ -2,8 +2,8 @@ import * as utxolib from '@bitgo/utxo-lib';
 import { Dimensions, VirtualSizes } from '@bitgo/unspents';
 import { Descriptor } from '@bitgo/wasm-miniscript';
 
-import { DescriptorMap } from './DescriptorMap';
-import { findDescriptorForInput } from './psbt';
+import { DescriptorMap } from './DescriptorMap.js';
+import { findDescriptorForInput } from './psbt/findDescriptors.js';
 
 function getScriptPubKeyLength(descType: string): number {
   // See https://bitcoinops.org/en/tools/calc-size/
diff --git a/modules/utxo-core/src/descriptor/index.ts b/modules/utxo-core/src/descriptor/index.ts
index 1d3d71aa61..2a923e744d 100644
--- a/modules/utxo-core/src/descriptor/index.ts
+++ b/modules/utxo-core/src/descriptor/index.ts
@@ -1,11 +1,11 @@
-export * from './psbt';
-export * from './address';
-export * from './DescriptorMap';
-export * from './derive';
-export * from './Output';
-export * from './VirtualSize';
-export * from './fromFixedScriptWallet';
-export * from './parse/PatternMatcher';
+export * from './psbt/index.js';
+export * from './address.js';
+export * from './DescriptorMap.js';
+export * from './derive.js';
+export * from './Output.js';
+export * from './VirtualSize.js';
+export * from './fromFixedScriptWallet.js';
+export * from './parse/PatternMatcher.js';
 
 /** @deprecated - import from @bitgo/utxo-core directly instead */
-export * from '../Output';
+export * from '../Output.js';
diff --git a/modules/utxo-core/src/descriptor/psbt/createPsbt.ts b/modules/utxo-core/src/descriptor/psbt/createPsbt.ts
index 996ef3905e..8e3807c1ce 100644
--- a/modules/utxo-core/src/descriptor/psbt/createPsbt.ts
+++ b/modules/utxo-core/src/descriptor/psbt/createPsbt.ts
@@ -1,12 +1,12 @@
-import { TapLeafScript } from 'bip174/src/lib/interfaces';
+import { TapLeafScript } from 'bip174/src/lib/interfaces.js';
 import * as utxolib from '@bitgo/utxo-lib';
 import { Descriptor, Miniscript } from '@bitgo/wasm-miniscript';
 
-import { DerivedDescriptorWalletOutput, WithOptDescriptor } from '../Output';
-import { Output } from '../../Output';
+import { DerivedDescriptorWalletOutput, WithOptDescriptor } from '../Output.js';
+import { Output } from '../../Output.js';
 
-import { toUtxoPsbt, toWrappedPsbt } from './wrap';
-import { assertSatisfiable } from './assertSatisfiable';
+import { toUtxoPsbt, toWrappedPsbt } from './wrap.js';
+import { assertSatisfiable } from './assertSatisfiable.js';
 
 /**
  * Non-Final (Replaceable)
diff --git a/modules/utxo-core/src/descriptor/psbt/findDescriptors.ts b/modules/utxo-core/src/descriptor/psbt/findDescriptors.ts
index 8326165a50..4dd1e19b48 100644
--- a/modules/utxo-core/src/descriptor/psbt/findDescriptors.ts
+++ b/modules/utxo-core/src/descriptor/psbt/findDescriptors.ts
@@ -9,10 +9,10 @@ It will probably only work correctly if all xpubs in the descriptor are derivabl
 We should take a look at a more robust and standard approach like this: https://github.com/bitcoin/bips/pull/1548
 
  */
-import { PsbtInput, PsbtOutput } from 'bip174/src/lib/interfaces';
+import { PsbtInput, PsbtOutput } from 'bip174/src/lib/interfaces.js';
 import { Descriptor } from '@bitgo/wasm-miniscript';
 
-import { DescriptorMap } from '../DescriptorMap';
+import { DescriptorMap } from '../DescriptorMap.js';
 
 type DescriptorWithoutIndex = { descriptor: Descriptor; index: undefined };
 
diff --git a/modules/utxo-core/src/descriptor/psbt/index.ts b/modules/utxo-core/src/descriptor/psbt/index.ts
index f442f5620d..daf1b1a983 100644
--- a/modules/utxo-core/src/descriptor/psbt/index.ts
+++ b/modules/utxo-core/src/descriptor/psbt/index.ts
@@ -1,6 +1,6 @@
-export * from './assertSatisfiable';
-export * from './createPsbt';
-export * from './parse';
-export * from './findDescriptors';
-export * from './wrap';
-export * from './sign';
+export * from './assertSatisfiable.js';
+export * from './createPsbt.js';
+export * from './parse.js';
+export * from './findDescriptors.js';
+export * from './wrap.js';
+export * from './sign.js';
diff --git a/modules/utxo-core/src/descriptor/psbt/parse.ts b/modules/utxo-core/src/descriptor/psbt/parse.ts
index 6e9822efbc..cf387871ca 100644
--- a/modules/utxo-core/src/descriptor/psbt/parse.ts
+++ b/modules/utxo-core/src/descriptor/psbt/parse.ts
@@ -1,11 +1,11 @@
 import { Descriptor } from '@bitgo/wasm-miniscript';
 import * as utxolib from '@bitgo/utxo-lib';
 
-import { DescriptorMap } from '../DescriptorMap';
-import { getVirtualSize } from '../VirtualSize';
+import { DescriptorMap } from '../DescriptorMap.js';
+import { getVirtualSize } from '../VirtualSize.js';
 
-import { findDescriptorForInput, findDescriptorForOutput } from './findDescriptors';
-import { assertSatisfiable } from './assertSatisfiable';
+import { findDescriptorForInput, findDescriptorForOutput } from './findDescriptors.js';
+import { assertSatisfiable } from './assertSatisfiable.js';
 
 export type ScriptId = { descriptor: Descriptor; index: number | undefined };
 
diff --git a/modules/utxo-core/src/index.ts b/modules/utxo-core/src/index.ts
index 31db24d010..c69ad47b14 100644
--- a/modules/utxo-core/src/index.ts
+++ b/modules/utxo-core/src/index.ts
@@ -1,8 +1,8 @@
-export * as bip65 from './bip65';
-export * as descriptor from './descriptor';
-export * as testutil from './testutil';
-export * as paygo from './paygo';
-export * as bip32utils from './bip32utils';
-export * from './dustThreshold';
-export * from './Output';
-export * from './xOnlyPubkey';
+export * as bip65 from './bip65/index.js';
+export * as descriptor from './descriptor/index.js';
+export * as testutil from './testutil/index.js';
+export * as paygo from './paygo/index.js';
+export * as bip32utils from './bip32utils.js';
+export * from './dustThreshold.js';
+export * from './Output.js';
+export * from './xOnlyPubkey.js';
diff --git a/modules/utxo-core/src/paygo/index.ts b/modules/utxo-core/src/paygo/index.ts
index 8555f440b6..4154b4b96f 100644
--- a/modules/utxo-core/src/paygo/index.ts
+++ b/modules/utxo-core/src/paygo/index.ts
@@ -1,2 +1,2 @@
-export * from './parsePayGoAttestation';
-export * from './psbt';
+export * from './parsePayGoAttestation.js';
+export * from './psbt/index.js';
diff --git a/modules/utxo-core/src/paygo/psbt/index.ts b/modules/utxo-core/src/paygo/psbt/index.ts
index bea5042737..a4bd1c6f5f 100644
--- a/modules/utxo-core/src/paygo/psbt/index.ts
+++ b/modules/utxo-core/src/paygo/psbt/index.ts
@@ -1 +1 @@
-export * from './payGoAddressProof';
+export * from './payGoAddressProof.js';
diff --git a/modules/utxo-core/src/paygo/psbt/payGoAddressProof.ts b/modules/utxo-core/src/paygo/psbt/payGoAddressProof.ts
index 24dc10361c..4a1d6491b6 100644
--- a/modules/utxo-core/src/paygo/psbt/payGoAddressProof.ts
+++ b/modules/utxo-core/src/paygo/psbt/payGoAddressProof.ts
@@ -1,8 +1,8 @@
 import * as utxolib from '@bitgo/utxo-lib';
-import { checkForOutput } from 'bip174/src/lib/utils';
+import { checkForOutput } from 'bip174/src/lib/utils.js';
 
-import { verifyMessage } from '../../bip32utils';
-import { createPayGoAttestationBuffer } from '../attestation';
+import { verifyMessage } from '../../bip32utils.js';
+import { createPayGoAttestationBuffer } from '../attestation.js';
 
 import {
   ErrorMultiplePayGoProof,
@@ -10,7 +10,7 @@ import {
   ErrorNoPayGoProof,
   ErrorOutputIndexOutOfBounds,
   ErrorPayGoAddressProofFailedVerification,
-} from './Errors';
+} from './Errors.js';
 
 /** This function adds the entropy and signature into the PSBT output unknown key vals.
  * We store the entropy so that we reconstruct the message <ENTROPY><ADDRESS><UUID>
diff --git a/modules/utxo-core/src/testutil/descriptor/descriptors.ts b/modules/utxo-core/src/testutil/descriptor/descriptors.ts
index 09144f8ecd..a477c9d917 100644
--- a/modules/utxo-core/src/testutil/descriptor/descriptors.ts
+++ b/modules/utxo-core/src/testutil/descriptor/descriptors.ts
@@ -3,8 +3,8 @@ import assert from 'assert';
 import { Miniscript, Descriptor, ast } from '@bitgo/wasm-miniscript';
 import { bip32, BIP32Interface } from '@bitgo/utxo-lib';
 
-import { DescriptorMap, PsbtParams } from '../../descriptor';
-import { getKeyTriple, Triple, KeyTriple } from '../key.utils';
+import { DescriptorMap, PsbtParams } from '../../descriptor/index.js';
+import { getKeyTriple, Triple, KeyTriple } from '../key.utils.js';
 
 export function getDefaultXPubs(seed?: string): Triple<string> {
   return getKeyTriple(seed).map((k) => k.neutered().toBase58()) as Triple<string>;
diff --git a/modules/utxo-core/src/testutil/descriptor/index.ts b/modules/utxo-core/src/testutil/descriptor/index.ts
index 1fe3266605..46a4788669 100644
--- a/modules/utxo-core/src/testutil/descriptor/index.ts
+++ b/modules/utxo-core/src/testutil/descriptor/index.ts
@@ -1,3 +1,3 @@
-export * from './descriptors';
-export * from './mock.utils';
-export * from './psbt.utils';
+export * from './descriptors.js';
+export * from './mock.utils.js';
+export * from './psbt.utils.js';
diff --git a/modules/utxo-core/src/testutil/descriptor/mock.utils.ts b/modules/utxo-core/src/testutil/descriptor/mock.utils.ts
index 487da08fc1..3511ab8235 100644
--- a/modules/utxo-core/src/testutil/descriptor/mock.utils.ts
+++ b/modules/utxo-core/src/testutil/descriptor/mock.utils.ts
@@ -6,9 +6,9 @@ import {
   createPsbt,
   createScriptPubKeyFromDescriptor,
   DerivedDescriptorTransactionInput,
-} from '../../descriptor';
+} from '../../descriptor/index.js';
 
-import { DescriptorTemplate, getDefaultXPubs, getDescriptor } from './descriptors';
+import { DescriptorTemplate, getDefaultXPubs, getDescriptor } from './descriptors.js';
 
 type MockOutputIdParams = { hash?: string; vout?: number };
 
diff --git a/modules/utxo-core/src/testutil/descriptor/psbt.utils.ts b/modules/utxo-core/src/testutil/descriptor/psbt.utils.ts
index 582b908ac6..5e17a6dbe6 100644
--- a/modules/utxo-core/src/testutil/descriptor/psbt.utils.ts
+++ b/modules/utxo-core/src/testutil/descriptor/psbt.utils.ts
@@ -1,6 +1,6 @@
 import * as utxolib from '@bitgo/utxo-lib';
 
-import { matchPath, PathElement, toPlainObject } from '../../../src/testutil';
+import { matchPath, PathElement, toPlainObject } from '../../../src/testutil/index.js';
 
 export function toPlainObjectFromPsbt(v: utxolib.Psbt): unknown {
   return toPlainObject(
diff --git a/modules/utxo-core/src/testutil/generatePayGoAttestationProof.utils.ts b/modules/utxo-core/src/testutil/generatePayGoAttestationProof.utils.ts
index 7a662db701..fe342e6729 100644
--- a/modules/utxo-core/src/testutil/generatePayGoAttestationProof.utils.ts
+++ b/modules/utxo-core/src/testutil/generatePayGoAttestationProof.utils.ts
@@ -2,7 +2,7 @@ import crypto from 'crypto';
 
 import { bufferutils } from '@bitgo/utxo-lib';
 
-import { Prefix } from '../paygo';
+import { Prefix } from '../paygo/index.js';
 
 /** We have a mirrored function similar to our hsm that generates our Bitcoin signed
  * message so that we can use for testing. This creates a random entropy as well using
diff --git a/modules/utxo-core/src/testutil/index.ts b/modules/utxo-core/src/testutil/index.ts
index f2d04b3c79..b04644ba05 100644
--- a/modules/utxo-core/src/testutil/index.ts
+++ b/modules/utxo-core/src/testutil/index.ts
@@ -1,5 +1,5 @@
-export * from './fixtures.utils';
-export * from './key.utils';
-export * from './toPlainObject.utils';
-export * from './generatePayGoAttestationProof.utils';
-export * from './trimMessagePrefix';
+export * from './fixtures.utils.js';
+export * from './key.utils.js';
+export * from './toPlainObject.utils.js';
+export * from './generatePayGoAttestationProof.utils.js';
+export * from './trimMessagePrefix.js';
diff --git a/modules/utxo-core/test/Output.ts b/modules/utxo-core/test/Output.ts
index 6bbe2fb3cd..5033986401 100644
--- a/modules/utxo-core/test/Output.ts
+++ b/modules/utxo-core/test/Output.ts
@@ -1,6 +1,6 @@
 import * as assert from 'assert';
 
-import { getFixedOutputSum, getMaxOutput, getOutputSum, isMaxOutput, toFixedOutputs } from '../src';
+import { getFixedOutputSum, getMaxOutput, getOutputSum, isMaxOutput, toFixedOutputs } from '../src/index.js';
 
 describe('Output', function () {
   const oBigInt = { value: 1n };
diff --git a/modules/utxo-core/test/bip32utils.ts b/modules/utxo-core/test/bip32utils.ts
index 0f5b94b088..a7ac84fa27 100644
--- a/modules/utxo-core/test/bip32utils.ts
+++ b/modules/utxo-core/test/bip32utils.ts
@@ -3,7 +3,7 @@ import * as assert from 'assert';
 
 import * as utxolib from '@bitgo/utxo-lib';
 
-import { signMessage, verifyMessage } from '../src/bip32utils';
+import { signMessage, verifyMessage } from '../src/bip32utils.js';
 
 describe('bip32utils', function () {
   function getSeedBuffers(length: number) {
@@ -21,7 +21,12 @@ describe('bip32utils', function () {
             const expectValid = message === otherMessage && key === otherKey;
             assert.strictEqual(verifyMessage(otherMessage, otherKey, signature, utxolib.networks.bitcoin), expectValid);
             assert.strictEqual(
-              verifyMessage(Buffer.from(otherMessage), otherKey, signature, utxolib.networks.bitcoin),
+              verifyMessage(
+                typeof otherMessage === 'string' ? Buffer.from(otherMessage) : otherMessage,
+                otherKey,
+                signature,
+                utxolib.networks.bitcoin
+              ),
               expectValid
             );
           });
diff --git a/modules/utxo-core/test/bip65/locktime.ts b/modules/utxo-core/test/bip65/locktime.ts
index c73cd19d2c..cc0e8f6e97 100644
--- a/modules/utxo-core/test/bip65/locktime.ts
+++ b/modules/utxo-core/test/bip65/locktime.ts
@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { encodeLocktime } from '../../src/bip65/locktime';
+import { encodeLocktime } from '../../src/bip65/locktime.js';
 
 describe('locktime', function () {
   it('encodes relative and absolute locktimes', function () {
diff --git a/modules/utxo-core/test/descriptor/Output.ts b/modules/utxo-core/test/descriptor/Output.ts
index a44c92ee48..bf7766f361 100644
--- a/modules/utxo-core/test/descriptor/Output.ts
+++ b/modules/utxo-core/test/descriptor/Output.ts
@@ -1,8 +1,8 @@
 import assert from 'assert';
 
-import { isExternalOutput, isInternalOutput, toDerivedDescriptorWalletOutput } from '../../src/descriptor/Output';
-import { getDescriptor } from '../../src/testutil/descriptor';
-import { createScriptPubKeyFromDescriptor } from '../../src/descriptor';
+import { isExternalOutput, isInternalOutput, toDerivedDescriptorWalletOutput } from '../../src/descriptor/Output.js';
+import { getDescriptor } from '../../src/testutil/descriptor/index.js';
+import { createScriptPubKeyFromDescriptor } from '../../src/descriptor/index.js';
 
 describe('decscriptor.Output', function () {
   const descriptor = getDescriptor('Wsh2Of3');
diff --git a/modules/utxo-core/test/descriptor/derive.ts b/modules/utxo-core/test/descriptor/derive.ts
index d8606848e0..e9a007c450 100644
--- a/modules/utxo-core/test/descriptor/derive.ts
+++ b/modules/utxo-core/test/descriptor/derive.ts
@@ -1,7 +1,7 @@
 import assert from 'assert';
 
-import { getDescriptor } from '../../src/testutil/descriptor';
-import { getDescriptorAtIndex, getDescriptorAtIndexCheckScript } from '../../src/descriptor/derive';
+import { getDescriptor } from '../../src/testutil/descriptor/index.js';
+import { getDescriptorAtIndex, getDescriptorAtIndexCheckScript } from '../../src/descriptor/derive.js';
 
 describe('derive', function () {
   const derivable = getDescriptor('Wsh2Of3');
diff --git a/modules/utxo-core/test/descriptor/fromFixedScriptWallet.ts b/modules/utxo-core/test/descriptor/fromFixedScriptWallet.ts
index a1a100162f..9ab7cacf51 100644
--- a/modules/utxo-core/test/descriptor/fromFixedScriptWallet.ts
+++ b/modules/utxo-core/test/descriptor/fromFixedScriptWallet.ts
@@ -6,7 +6,7 @@ import { Descriptor } from '@bitgo/wasm-miniscript';
 import {
   getDescriptorForScriptType,
   getNamedDescriptorsForRootWalletKeys,
-} from '../../src/descriptor/fromFixedScriptWallet';
+} from '../../src/descriptor/fromFixedScriptWallet.js';
 
 function getRootWalletKeys(derivationPrefixes?: utxolib.bitgo.Triple<string>): utxolib.bitgo.RootWalletKeys {
   // This is a fixed script wallet, so we use a fixed key triple.
diff --git a/modules/utxo-core/test/descriptor/parse/PatternMatcher.ts b/modules/utxo-core/test/descriptor/parse/PatternMatcher.ts
index 3e82020c54..8bdf29fc39 100644
--- a/modules/utxo-core/test/descriptor/parse/PatternMatcher.ts
+++ b/modules/utxo-core/test/descriptor/parse/PatternMatcher.ts
@@ -2,9 +2,9 @@ import assert from 'assert';
 
 import { Descriptor, ast } from '@bitgo/wasm-miniscript';
 
-import { getKey } from '../../../src/testutil';
-import { toXOnlyPublicKey } from '../../../src';
-import { PatternMatcher, Pattern } from '../../../src/descriptor/parse/PatternMatcher';
+import { getKey } from '../../../src/testutil/index.js';
+import { toXOnlyPublicKey } from '../../../src/index.js';
+import { PatternMatcher, Pattern } from '../../../src/descriptor/parse/PatternMatcher.js';
 
 function key32(seed: string): Buffer {
   // return x-only public key from seed
diff --git a/modules/utxo-core/test/descriptor/psbt/VirtualSize.ts b/modules/utxo-core/test/descriptor/psbt/VirtualSize.ts
index 9fed1ae7c4..978fe0a24a 100644
--- a/modules/utxo-core/test/descriptor/psbt/VirtualSize.ts
+++ b/modules/utxo-core/test/descriptor/psbt/VirtualSize.ts
@@ -5,16 +5,16 @@ import {
   getInputVSizesForDescriptors,
   getVirtualSize,
   getVirtualSizeEstimateForPsbt,
-} from '../../../src/descriptor/VirtualSize';
+} from '../../../src/descriptor/VirtualSize.js';
 import {
   DescriptorTemplate,
   getDefaultXPubs,
   getDescriptor,
   getDescriptorMap,
   mockPsbtDefault,
-} from '../../../src/testutil/descriptor';
-import { getKeyTriple } from '../../../src/testutil';
-import { finalizePsbt } from '../../../src/descriptor';
+} from '../../../src/testutil/descriptor/index.js';
+import { getKeyTriple } from '../../../src/testutil/index.js';
+import { finalizePsbt } from '../../../src/descriptor/index.js';
 
 describe('VirtualSize', function () {
   describe('getInputVSizesForDescriptorWallet', function () {
diff --git a/modules/utxo-core/test/descriptor/psbt/assertSatisfiable.ts b/modules/utxo-core/test/descriptor/psbt/assertSatisfiable.ts
index 4263ae88dd..1d1ce0d74f 100644
--- a/modules/utxo-core/test/descriptor/psbt/assertSatisfiable.ts
+++ b/modules/utxo-core/test/descriptor/psbt/assertSatisfiable.ts
@@ -2,8 +2,8 @@ import * as assert from 'assert';
 
 import { Descriptor } from '@bitgo/wasm-miniscript';
 
-import { getDefaultXPubs } from '../../../src/testutil/descriptor';
-import { getRequiredLocktime } from '../../../src/descriptor';
+import { getDefaultXPubs } from '../../../src/testutil/descriptor/index.js';
+import { getRequiredLocktime } from '../../../src/descriptor/index.js';
 
 function d(s: string): Descriptor {
   return Descriptor.fromString(s, 'derivable');
diff --git a/modules/utxo-core/test/descriptor/psbt/findDescriptors.ts b/modules/utxo-core/test/descriptor/psbt/findDescriptors.ts
index 40c8619123..f537df0b51 100644
--- a/modules/utxo-core/test/descriptor/psbt/findDescriptors.ts
+++ b/modules/utxo-core/test/descriptor/psbt/findDescriptors.ts
@@ -1,7 +1,12 @@
 import * as assert from 'assert';
 
-import { DescriptorTemplate, getDefaultXPubs, getDescriptor, mockPsbt } from '../../../src/testutil/descriptor';
-import { findDescriptorForInput, findDescriptorForOutput } from '../../../src/descriptor';
+import {
+  DescriptorTemplate,
+  getDefaultXPubs,
+  getDescriptor,
+  mockPsbt,
+} from '../../../src/testutil/descriptor/index.js';
+import { findDescriptorForInput, findDescriptorForOutput } from '../../../src/descriptor/index.js';
 
 function describeWithTemplates(templateSelf: DescriptorTemplate, templateOther: DescriptorTemplate) {
   describe(`parsePsbt [${templateSelf},${templateOther}]`, function () {
diff --git a/modules/utxo-core/test/descriptor/psbt/psbt.ts b/modules/utxo-core/test/descriptor/psbt/psbt.ts
index af339a2d22..332656daa4 100644
--- a/modules/utxo-core/test/descriptor/psbt/psbt.ts
+++ b/modules/utxo-core/test/descriptor/psbt/psbt.ts
@@ -1,11 +1,19 @@
 import assert from 'assert';
+import path from 'path';
+import { fileURLToPath } from 'url';
 
 import * as utxolib from '@bitgo/utxo-lib';
 import { BIP32Interface, ECPair, ECPairInterface } from '@bitgo/utxo-lib';
 import { Descriptor, Miniscript } from '@bitgo/wasm-miniscript';
 
-import { PsbtParams, parse, toUtxoPsbt, toWrappedPsbt, ParsedDescriptorTransaction } from '../../../src/descriptor';
-import { getFixture, getKeyTriple } from '../../../src/testutil';
+import {
+  PsbtParams,
+  parse,
+  toUtxoPsbt,
+  toWrappedPsbt,
+  ParsedDescriptorTransaction,
+} from '../../../src/descriptor/index.js';
+import { getFixture, getKeyTriple } from '../../../src/testutil/index.js';
 import {
   containsKey,
   DescriptorTemplate,
@@ -16,8 +24,8 @@ import {
   mockPsbtDefault,
   toPlainObjectFromPsbt,
   toPlainObjectFromTx,
-} from '../../../src/testutil/descriptor';
-import { getNewSignatureCount, signWithKey } from '../../../src/descriptor/psbt/sign';
+} from '../../../src/testutil/descriptor/index.js';
+import { getNewSignatureCount, signWithKey } from '../../../src/descriptor/psbt/sign.js';
 
 function normalize(v: unknown): unknown {
   if (typeof v === 'bigint') {
@@ -45,7 +53,9 @@ function normalize(v: unknown): unknown {
 }
 
 async function assertEqualsFixture(t: string, filename: string, value: unknown) {
-  filename = __dirname + '/../../../../test/descriptor/psbt/fixtures/' + t + '.' + filename;
+  const __filename = fileURLToPath(import.meta.url);
+  const __dirname = path.dirname(__filename);
+  filename = __dirname + '/fixtures/' + t + '.' + filename;
   const nv = normalize(value);
   assert.deepStrictEqual(nv, await getFixture(filename, nv));
 }
diff --git a/modules/utxo-core/test/dustThreshold.ts b/modules/utxo-core/test/dustThreshold.ts
index cdc29fbf98..b3f89e3429 100644
--- a/modules/utxo-core/test/dustThreshold.ts
+++ b/modules/utxo-core/test/dustThreshold.ts
@@ -2,7 +2,7 @@ import assert from 'assert';
 
 import * as utxolib from '@bitgo/utxo-lib';
 
-import { getDustThresholdSat } from '../src/dustThreshold';
+import { getDustThresholdSat } from '../src/dustThreshold.js';
 
 describe('getDustThresholdSat', function () {
   it('has expected values', function () {
diff --git a/modules/utxo-core/test/paygo/attestation.ts b/modules/utxo-core/test/paygo/attestation.ts
index 26baf23b1e..285be1107b 100644
--- a/modules/utxo-core/test/paygo/attestation.ts
+++ b/modules/utxo-core/test/paygo/attestation.ts
@@ -1,9 +1,9 @@
 import assert from 'assert';
 
-import { createPayGoAttestationBuffer } from '../../src/paygo/attestation';
-import { generatePayGoAttestationProof } from '../../src/testutil';
+import { createPayGoAttestationBuffer } from '../../src/paygo/attestation.js';
+import { generatePayGoAttestationProof } from '../../src/testutil/index.js';
 
-import { addressProofEntropy, addressProofMsgBuffer, addressToVerify, network } from './psbt/payGoAddressProof';
+import { addressProofEntropy, addressProofMsgBuffer, addressToVerify, network } from './psbt/payGoAddressProof.js';
 
 describe('createPayGoAttestationBuffer', () => {
   it('should create a PayGo Attestation proof matching with original proof', () => {
diff --git a/modules/utxo-core/test/paygo/parsePayGoAttestation.ts b/modules/utxo-core/test/paygo/parsePayGoAttestation.ts
index b58bb3bf69..17bc167ff5 100644
--- a/modules/utxo-core/test/paygo/parsePayGoAttestation.ts
+++ b/modules/utxo-core/test/paygo/parsePayGoAttestation.ts
@@ -1,8 +1,8 @@
 import * as assert from 'assert';
 
-import { parsePayGoAttestation } from '../../src/paygo';
-import { generatePayGoAttestationProof } from '../../src/testutil';
-import { NIL_UUID } from '../../src/paygo/attestation';
+import { parsePayGoAttestation } from '../../src/paygo/index.js';
+import { generatePayGoAttestationProof } from '../../src/testutil/index.js';
+import { NIL_UUID } from '../../src/paygo/attestation.js';
 
 const addressFromPubKeyBase58 = 'bitgoAddressToExtract';
 const bufferAddressPubKeyB58 = Buffer.from(addressFromPubKeyBase58);
diff --git a/modules/utxo-core/test/paygo/psbt/payGoAddressProof.ts b/modules/utxo-core/test/paygo/psbt/payGoAddressProof.ts
index 1bd8518f78..1f28ff105c 100644
--- a/modules/utxo-core/test/paygo/psbt/payGoAddressProof.ts
+++ b/modules/utxo-core/test/paygo/psbt/payGoAddressProof.ts
@@ -2,20 +2,20 @@ import assert from 'assert';
 import crypto from 'crypto';
 
 import * as utxolib from '@bitgo/utxo-lib';
-import { decodeProprietaryKey } from 'bip174/src/lib/proprietaryKeyVal';
-import { KeyValue } from 'bip174/src/lib/interfaces';
-import { checkForOutput } from 'bip174/src/lib/utils';
+import { decodeProprietaryKey } from 'bip174/src/lib/proprietaryKeyVal.js';
+import { KeyValue } from 'bip174/src/lib/interfaces.js';
+import { checkForOutput } from 'bip174/src/lib/utils.js';
 
 import {
   addPayGoAddressProof,
   getPayGoAddressProofOutputIndex,
   psbtOutputIncludesPaygoAddressProof,
   verifyPayGoAddressProof,
-} from '../../../src/paygo/psbt/payGoAddressProof';
-import { generatePayGoAttestationProof } from '../../../src/testutil/generatePayGoAttestationProof.utils';
-import { trimMessagePrefix } from '../../../src/testutil/trimMessagePrefix';
-import { signMessage } from '../../../src/bip32utils';
-import { NIL_UUID } from '../../../src/paygo/attestation';
+} from '../../../src/paygo/psbt/payGoAddressProof.js';
+import { generatePayGoAttestationProof } from '../../../src/testutil/generatePayGoAttestationProof.utils.js';
+import { trimMessagePrefix } from '../../../src/testutil/trimMessagePrefix.js';
+import { signMessage } from '../../../src/bip32utils.js';
+import { NIL_UUID } from '../../../src/paygo/attestation.js';
 
 // To construct our PSBTs
 export const network = utxolib.networks.bitcoin;
diff --git a/modules/utxo-core/test/xOnlyPubkey.ts b/modules/utxo-core/test/xOnlyPubkey.ts
index 88a9faf1e6..2513a59547 100644
--- a/modules/utxo-core/test/xOnlyPubkey.ts
+++ b/modules/utxo-core/test/xOnlyPubkey.ts
@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { toXOnlyPublicKey } from '../src';
+import { toXOnlyPublicKey } from '../src/index.js';
 
 describe('xOnlyPubkey', function () {
   it('converts to X-Only pubkey', function () {
diff --git a/modules/utxo-core/tsconfig.json b/modules/utxo-core/tsconfig.json
index 6616905289..6212f6f8c5 100644
--- a/modules/utxo-core/tsconfig.json
+++ b/modules/utxo-core/tsconfig.json
@@ -3,6 +3,8 @@
   "compilerOptions": {
     "outDir": "./dist",
     "rootDir": "./",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
     "esModuleInterop": true,
     "allowJs": false,
     "strict": true