diff --git a/rust/src/transaction_builder.rs b/rust/src/transaction_builder.rs
index 67dfe7c..8460181 100644
--- a/rust/src/transaction_builder.rs
+++ b/rust/src/transaction_builder.rs
@@ -155,6 +155,10 @@ impl UnsignedTransaction {
         max_fee: u128,
         priority_fee_bips: u64,
         gas_limit: Option<Gas>,
+        /// Uniqueness generation value. Defaults to the current unix timestamp
+        /// in milliseconds, giving a ~5-second deduplication window with the
+        /// sequencer's default 5000-generation window.
+        generation: Option<u64>,
         client: &Client,
     ) -> SDKResult<UnsignedTransaction> {
         // Check whether the call message was part of the schema validation.
@@ -163,16 +167,14 @@ impl UnsignedTransaction {
         }
 
         let runtime_call = RuntimeCall::Exchange(call_message);
-        // Microseconds, not milliseconds: the sequencer's uniqueness check
-        // compares against `latest_known_generation` which is stored in μs
-        // (16-digit unix-time value). A ms timestamp (13 digits) is treated
-        // as ancient (~1000x older than the cutoff) and rejected with
-        // CheckUniquenessFailed.
-        let timestamp = SystemTime::now()
-            .duration_since(UNIX_EPOCH)
-            .map_err(|_| SDKError::SystemTimeError)?
-            .as_micros() as u64;
-        let uniqueness = UniquenessData::Generation(timestamp);
+        let generation = match generation {
+            Some(g) => g,
+            None => SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .map_err(|_| SDKError::SystemTimeError)?
+                .as_millis() as u64,
+        };
+        let uniqueness = UniquenessData::Generation(generation);
         let details = TxDetails {
             chain_id: client.chain_id(),
             max_fee: Amount(max_fee),
@@ -348,6 +350,7 @@ impl Transaction {
         max_fee: Option<u128>,
         priority_fee_bips: Option<u64>,
         gas_limit: Option<Gas>,
+        generation: Option<u64>,
         signer: Option<&Keypair>,
         client: &Client,
     ) -> SDKResult<SignedTransaction> {
@@ -363,6 +366,7 @@ impl Transaction {
             .max_fee(max_fee)
             .priority_fee_bips(priority_fee_bips)
             .maybe_gas_limit(gas_limit)
+            .maybe_generation(generation)
             .client(client)
             .build()?;
 
diff --git a/wasm/README.md b/wasm/README.md
index 7cc63cc..e59d68e 100644
--- a/wasm/README.md
+++ b/wasm/README.md
@@ -111,6 +111,18 @@ const tx = Transaction.builder()
 await client.sendTransaction(tx);
 ```
 
+By default the uniqueness generation is a millisecond unix timestamp, giving
+a ~5-second deduplication window. Override with `.generation()` to pass any
+value — for example a microsecond timestamp for a ~5ms window:
+
+```typescript
+const tx = Transaction.builder()
+    .callMessage(msg)
+    .generation(BigInt(Date.now()) * 1000n)  // microseconds
+    .signer(keypair)
+    .send(client);
+```
+
 ### External Signing
 
 For hardware wallets or external signing services that can sign the standard
diff --git a/wasm/src/transaction_builder.rs b/wasm/src/transaction_builder.rs
index 74094cf..31124df 100644
--- a/wasm/src/transaction_builder.rs
+++ b/wasm/src/transaction_builder.rs
@@ -382,6 +382,7 @@ impl WasmTransactionEntry {
 /// - `maxFee` - Maximum fee willing to pay (in base units)
 /// - `priorityFeeBips` - Priority fee in basis points
 /// - `gasLimit` - Optional gas limit [ref_time, proof_size]
+/// - `generation` - Uniqueness generation value (default: current unix timestamp in milliseconds)
 /// - `signer` - Keypair to sign the transaction (not required for `buildUnsigned`)
 #[wasm_bindgen(js_name = TransactionBuilder)]
 pub struct WasmTransactionBuilder {
@@ -389,6 +390,7 @@ pub struct WasmTransactionBuilder {
     max_fee: Option<u64>,
     priority_fee_bips: Option<u64>,
     gas_limit: Option<[u64; 2]>,
+    generation: Option<u64>,
     signer: Option<WasmKeypair>,
 }
 
@@ -399,6 +401,7 @@ impl WasmTransactionBuilder {
             max_fee: None,
             priority_fee_bips: None,
             gas_limit: None,
+            generation: None,
             signer: None,
         }
     }
@@ -436,6 +439,18 @@ impl WasmTransactionBuilder {
         self
     }
 
+    /// Override the uniqueness generation value.
+    ///
+    /// Defaults to the current unix timestamp in milliseconds, giving a
+    /// ~5-second deduplication window with the sequencer's 5000-generation window.
+    /// Pass a microsecond timestamp for a ~5ms window, or any other value as needed.
+    /// @param {bigint} generation - The generation value to use.
+    /// @returns {TransactionBuilder}
+    pub fn generation(mut self, generation: u64) -> WasmTransactionBuilder {
+        self.generation = Some(generation);
+        self
+    }
+
     /// Set the keypair used to sign this transaction.
     pub fn signer(mut self, keypair: WasmKeypair) -> WasmTransactionBuilder {
         self.signer = Some(keypair);
@@ -470,6 +485,7 @@ impl WasmTransactionBuilder {
             .max_fee(max_fee)
             .priority_fee_bips(priority_fee_bips)
             .maybe_gas_limit(gas_limit)
+            .maybe_generation(self.generation)
             .client(&client.inner)
             .build()?;
 
@@ -489,6 +505,7 @@ impl WasmTransactionBuilder {
             .maybe_max_fee(max_fee)
             .maybe_priority_fee_bips(self.priority_fee_bips)
             .maybe_gas_limit(gas_limit)
+            .maybe_generation(self.generation)
             .maybe_signer(signer_ref)
             .client(&client.inner)
             .build()?;