diff --git a/.changeset/grumpy-swans-judge.md b/.changeset/grumpy-swans-judge.md
new file mode 100644
index 0000000..957b2be
--- /dev/null
+++ b/.changeset/grumpy-swans-judge.md
@@ -0,0 +1,5 @@
+---
+"@across-protocol/integrator-sdk": patch
+---
+
+stricter integrator id check
diff --git a/apps/example/app/ethers/components/Bridge.tsx b/apps/example/app/ethers/components/Bridge.tsx
index 343f344..390822d 100644
--- a/apps/example/app/ethers/components/Bridge.tsx
+++ b/apps/example/app/ethers/components/Bridge.tsx
@@ -17,7 +17,6 @@ const chains = [mainnet, arbitrum];
 const sdk = AcrossClient.create({
   chains,
   useTestnet: false,
-  integratorId: "TEST",
   logLevel: "DEBUG",
 });
 
diff --git a/apps/example/lib/across.tsx b/apps/example/lib/across.tsx
index db0965e..ff3a46b 100644
--- a/apps/example/lib/across.tsx
+++ b/apps/example/lib/across.tsx
@@ -9,7 +9,6 @@ export const SUPPORTED_CHAINS = MAINNET_SUPPORTED_CHAINS;
 const sdk = AcrossClient.create({
   chains: [...SUPPORTED_CHAINS],
   useTestnet: false,
-  integratorId: "TEST",
   logLevel: "DEBUG",
 });
 
diff --git a/apps/example/scripts/sdk.ts b/apps/example/scripts/sdk.ts
index cca91c2..9130dfb 100644
--- a/apps/example/scripts/sdk.ts
+++ b/apps/example/scripts/sdk.ts
@@ -46,7 +46,6 @@ async function main() {
   const client = AcrossClient.create({
     chains,
     useTestnet: false,
-    integratorId: "TEST",
     logLevel: "DEBUG",
     walletClient,
     tenderly: {
diff --git a/packages/sdk/src/actions/executeQuote.ts b/packages/sdk/src/actions/executeQuote.ts
index 0c86614..8b07b9c 100644
--- a/packages/sdk/src/actions/executeQuote.ts
+++ b/packages/sdk/src/actions/executeQuote.ts
@@ -1,6 +1,7 @@
 import {
   Address,
   Hash,
+  Hex,
   parseAbi,
   SimulateContractReturnType,
   TransactionReceipt,
@@ -112,7 +113,7 @@ export type ExecuteQuoteParams = {
   /**
    * An identifier for the integrator.
    */
-  integratorId: string;
+  integratorId: Hex;
   /**
    * The deposit to execute. Should be taken from return value of {@link getQuote}.
    */
diff --git a/packages/sdk/src/actions/simulateDepositTx.ts b/packages/sdk/src/actions/simulateDepositTx.ts
index ebee073..49e58ad 100644
--- a/packages/sdk/src/actions/simulateDepositTx.ts
+++ b/packages/sdk/src/actions/simulateDepositTx.ts
@@ -1,4 +1,5 @@
 import {
+  Hex,
   PublicClient,
   SimulateContractReturnType,
   WalletClient,
@@ -18,7 +19,7 @@ export type SimulateDepositTxParams = {
   deposit: Quote["deposit"] & {
     fillDeadline?: number;
   };
-  integratorId: string;
+  integratorId: Hex;
   logger?: LoggerT;
 };
 
diff --git a/packages/sdk/src/client.ts b/packages/sdk/src/client.ts
index 60133d9..a28ad43 100644
--- a/packages/sdk/src/client.ts
+++ b/packages/sdk/src/client.ts
@@ -2,6 +2,7 @@ import {
   Chain,
   ContractFunctionExecutionError,
   encodeFunctionData,
+  Hex,
 } from "viem";
 import {
   getAvailableRoutes,
@@ -43,6 +44,7 @@ import {
   getSupportedChains,
   simulateTxOnTenderly,
   TenderlySimulateTxParams,
+  assertValidIntegratorId,
 } from "./utils";
 import {
   AcrossApiSimulationError,
@@ -53,12 +55,11 @@ import {
   ConfiguredPublicClient,
   ConfiguredPublicClientMap,
   ConfiguredWalletClient,
-  Deposit,
 } from "./types";
 
 const CLIENT_DEFAULTS = {
   pollingInterval: 3_000,
-  integratorId: "INTEGRATOR_SDK",
+  integratorId: "0xdead",
   logLevel: "ERROR",
 } as const;
 
@@ -67,7 +68,7 @@ export type AcrossClientOptions = {
   /**
    * An identifier representing the integrator.
    */
-  integratorId?: string;
+  integratorId?: Hex;
   /**
    * The chains to use for the Across API. Should be imported from `viem/chains`.
    */
@@ -135,7 +136,7 @@ export type AcrossClientOptions = {
 export class AcrossClient {
   private static instance: AcrossClient | null = null;
 
-  private integratorId: string;
+  private integratorId: Hex;
   private publicClients: ConfiguredPublicClientMap;
   private walletClient?: ConfiguredWalletClient;
   private apiUrl: string;
@@ -159,7 +160,10 @@ export class AcrossClient {
   }
 
   private constructor(args: AcrossClientOptions) {
-    this.integratorId = args?.integratorId ?? CLIENT_DEFAULTS.integratorId;
+    const integratorId = args?.integratorId ?? CLIENT_DEFAULTS.integratorId;
+    assertValidIntegratorId(integratorId);
+
+    this.integratorId = integratorId;
     this.walletClient = args?.walletClient;
     this.publicClients = configurePublicClients(
       args.chains,
diff --git a/packages/sdk/src/utils/hex.ts b/packages/sdk/src/utils/hex.ts
index 6c3d768..77e7314 100644
--- a/packages/sdk/src/utils/hex.ts
+++ b/packages/sdk/src/utils/hex.ts
@@ -1,11 +1,35 @@
-import { concat, Hex, toHex } from "viem";
+import { concat, Hex, isHex } from "viem";
 
 export const DOMAIN_CALLDATA_DELIMITER = "0x1dc0de";
 
-export function tagIntegratorId(integratorId: string, txData: Hex) {
-  return concat([txData, DOMAIN_CALLDATA_DELIMITER, toHex(integratorId)]);
+export function tagIntegratorId(integratorId: Hex, txData: Hex) {
+  assertValidIntegratorId(integratorId);
+
+  return concat([txData, DOMAIN_CALLDATA_DELIMITER, integratorId]);
+}
+
+export function getIntegratorDataSuffix(integratorId: Hex) {
+  assertValidIntegratorId(integratorId);
+
+  return concat([DOMAIN_CALLDATA_DELIMITER, integratorId]);
 }
 
-export function getIntegratorDataSuffix(integratorId: string) {
-  return concat([DOMAIN_CALLDATA_DELIMITER, toHex(integratorId)]);
+export function isValidIntegratorId(integratorId: string) {
+  return (
+    isHex(integratorId) &&
+    // "0x" + 2 bytes = 6 hex characters
+    integratorId.length === 6
+  );
+}
+
+export function assertValidIntegratorId(
+  integratorId: string,
+): integratorId is Hex {
+  if (!isValidIntegratorId(integratorId)) {
+    throw new Error(
+      `Invalid integrator ID: ${integratorId}. Needs to be 2 bytes hex string.`,
+    );
+  }
+
+  return true;
 }
diff --git a/packages/sdk/test/utils/logger.test.ts b/packages/sdk/test/utils/logger.test.ts
index 999994c..26d8887 100644
--- a/packages/sdk/test/utils/logger.test.ts
+++ b/packages/sdk/test/utils/logger.test.ts
@@ -4,7 +4,6 @@ import { hardhat } from "viem/chains";
 
 const client = AcrossClient.create({
   useTestnet: true,
-  integratorId: "TEST_ID",
   logLevel: "WARN",
   chains: [hardhat],
 });