diff --git a/modules/core/src-js/smithy4s/Timestamp.scala b/modules/core/src-js/smithy4s/Timestamp.scala
index f59d5e6e0..fbfec6f8a 100644
--- a/modules/core/src-js/smithy4s/Timestamp.scala
+++ b/modules/core/src-js/smithy4s/Timestamp.scala
@@ -81,25 +81,25 @@ case class Timestamp private (epochSecond: Long, nano: Int) {
         append2Digits(day, s.append(' '))
         s.append(' ').append(months(month - 1))
         append4Digits(year, s.append(' '))
-        appendTime(secsOfDay, s.append(' '))
+        appendTime(secsOfDay, s.append(' '), addSeparator = true)
         appendNano(nano, s)
         s.append(" GMT").toString
       case 2 =>
         append4Digits(year, s)
-        append2Digits(month, s.append('-'))
-        append2Digits(day, s.append('-'))
+        append2Digits(month, s)
+        append2Digits(day, s)
         s.toString
       case 3 =>
         append4Digits(year, s)
-        append2Digits(month, s.append('-'))
-        append2Digits(day, s.append('-'))
-        appendTime(secsOfDay, s.append('T'))
+        append2Digits(month, s)
+        append2Digits(day, s)
+        appendTime(secsOfDay, s.append('T'), addSeparator = false)
         s.append('Z').toString
       case _ =>
         append4Digits(year, s)
         append2Digits(month, s.append('-'))
         append2Digits(day, s.append('-'))
-        appendTime(secsOfDay, s.append('T'))
+        appendTime(secsOfDay, s.append('T'), addSeparator = true)
         appendNano(nano, s)
         s.append('Z').toString
     }
@@ -114,15 +114,23 @@ case class Timestamp private (epochSecond: Long, nano: Int) {
 
   private[this] def appendTime(
       secsOfDay: Int,
-      s: java.lang.StringBuilder
+      s: java.lang.StringBuilder,
+      addSeparator: Boolean
   ): Unit = {
     val minutesOfDay = secsOfDay / 60
     val hour = minutesOfDay / 60
     val minute = minutesOfDay - hour * 60
     val second = secsOfDay - minutesOfDay * 60
-    append2Digits(hour, s)
-    append2Digits(minute, s.append(':'))
-    append2Digits(second, s.append(':'))
+
+    if (addSeparator) {
+      append2Digits(hour, s)
+      append2Digits(minute, s.append(':'))
+      append2Digits(second, s.append(':'))
+    } else {
+      append2Digits(hour, s)
+      append2Digits(minute, s)
+      append2Digits(second, s)
+    }
   }
 
   private[this] def appendNano(nano: Int, s: java.lang.StringBuilder): Unit =
diff --git a/modules/core/src-jvm-native/smithy4s/Timestamp.scala b/modules/core/src-jvm-native/smithy4s/Timestamp.scala
index d2890c098..dff0b9040 100644
--- a/modules/core/src-jvm-native/smithy4s/Timestamp.scala
+++ b/modules/core/src-jvm-native/smithy4s/Timestamp.scala
@@ -73,25 +73,25 @@ case class Timestamp private (epochSecond: Long, nano: Int)
         append2Digits(day, s.append(' '))
         s.append(' ').append(Timestamp.months(month - 1))
         append4Digits(year, s.append(' '))
-        appendTime(secsOfDay, s.append(' '))
+        appendTime(secsOfDay, s.append(' '), addSeparator = true)
         appendNano(nano, s)
         s.append(" GMT").toString
       case 2 =>
         append4Digits(year, s)
-        append2Digits(month, s.append('-'))
-        append2Digits(day, s.append('-'))
+        append2Digits(month, s)
+        append2Digits(day, s)
         s.toString
       case 3 =>
         append4Digits(year, s)
-        append2Digits(month, s.append('-'))
-        append2Digits(day, s.append('-'))
-        appendTime(secsOfDay, s.append('T'))
+        append2Digits(month, s)
+        append2Digits(day, s)
+        appendTime(secsOfDay, s.append('T'), addSeparator = false)
         s.append('Z').toString
       case _ =>
         append4Digits(year, s)
         append2Digits(month, s.append('-'))
         append2Digits(day, s.append('-'))
-        appendTime(secsOfDay, s.append('T'))
+        appendTime(secsOfDay, s.append('T'), addSeparator = true)
         appendNano(nano, s)
         s.append('Z').toString
     }
@@ -106,15 +106,23 @@ case class Timestamp private (epochSecond: Long, nano: Int)
 
   private[this] def appendTime(
       secsOfDay: Int,
-      s: java.lang.StringBuilder
+      s: java.lang.StringBuilder,
+      addSeparator: Boolean
   ): Unit = {
     val y1 =
       secsOfDay * 1193047L // Based on James Anhalt's algorithm: https://jk-jeon.github.io/posts/2022/02/jeaiii-algorithm/
     val y2 = (y1 & 0xffffffffL) * 60
     val y3 = (y2 & 0xffffffffL) * 60
-    append2Digits((y1 >> 32).toInt, s)
-    append2Digits((y2 >> 32).toInt, s.append(':'))
-    append2Digits((y3 >> 32).toInt, s.append(':'))
+
+    if (addSeparator) {
+      append2Digits((y1 >> 32).toInt, s)
+      append2Digits((y2 >> 32).toInt, s.append(':'))
+      append2Digits((y3 >> 32).toInt, s.append(':'))
+    } else {
+      append2Digits((y1 >> 32).toInt, s)
+      append2Digits((y2 >> 32).toInt, s)
+      append2Digits((y3 >> 32).toInt, s)
+    }
   }
 
   private[this] def appendNano(nano: Int, s: java.lang.StringBuilder): Unit =
diff --git a/modules/core/test/src-js/smithy4s/TimestampSpec.scala b/modules/core/test/src-js/smithy4s/TimestampSpec.scala
index 314f592c8..64a832e29 100644
--- a/modules/core/test/src-js/smithy4s/TimestampSpec.scala
+++ b/modules/core/test/src-js/smithy4s/TimestampSpec.scala
@@ -127,4 +127,36 @@ class TimestampSpec() extends munit.FunSuite with munit.ScalaCheckSuite {
       expect.same(parsed, None)
     }
   }
+
+  property("Converts to concise date format") {
+    forAll { (i: Date) =>
+      val epochSecond = (i.valueOf() / 1000).toLong
+      val nano = (i.valueOf() % 1000).toInt * 1000000
+      val ts = Timestamp(epochSecond, nano)
+      val formatted = ts.conciseDate
+      val year = i.getUTCFullYear().toInt
+      val month = i.getUTCMonth().toInt + 1 // in js month is 0-11
+      val date = i.getUTCDate().toInt
+      val expected = f"$year%04d$month%02d$date%02d"
+      expect.same(formatted, expected)
+    }
+  }
+
+  property("Converts to concise date time format") {
+    forAll { (i: Date) =>
+      val epochSecond = (i.valueOf() / 1000).toLong
+      val nano = (i.valueOf() % 1000).toInt * 1000000
+      val ts = Timestamp(epochSecond = epochSecond, nano = nano)
+      val formatted = ts.conciseDateTime
+      val year = i.getUTCFullYear().toInt
+      val month = i.getUTCMonth().toInt + 1 // in js month is 0-11
+      val date = i.getUTCDate().toInt
+      val hours = i.getUTCHours().toInt
+      val minutes = i.getUTCMinutes().toInt
+      val seconds = i.getUTCSeconds().toInt
+      val expected =
+        f"$year%04d$month%02d$date%02dT$hours%02d$minutes%02d$seconds%02dZ"
+      expect.same(formatted, expected)
+    }
+  }
 }
diff --git a/modules/core/test/src-jvm/smithy4s/TimestampSpec.scala b/modules/core/test/src-jvm/smithy4s/TimestampSpec.scala
index d39ca6a00..c784039fe 100644
--- a/modules/core/test/src-jvm/smithy4s/TimestampSpec.scala
+++ b/modules/core/test/src-jvm/smithy4s/TimestampSpec.scala
@@ -138,4 +138,30 @@ class TimestampSpec() extends munit.FunSuite with munit.ScalaCheckSuite {
       expect.same(parsed, None)
     }
   }
+
+  private val conciseDateFormatter = DateTimeFormatter
+    .ofPattern("yyyyMMdd", Locale.ENGLISH)
+    .withZone(ZoneOffset.UTC)
+
+  private val conciseDateTimeFormatter = DateTimeFormatter
+    .ofPattern("yyyyMMdd'T'HHmmssX", Locale.ENGLISH)
+    .withZone(ZoneOffset.UTC)
+
+  property("Converts to concise date format") {
+    forAll { (i: Instant) =>
+      val ts = Timestamp(i.getEpochSecond, i.getNano)
+      val formatted = ts.conciseDate
+      val expected = conciseDateFormatter.format(i)
+      expect.same(formatted, expected)
+    }
+  }
+
+  property("Converts to concise date time format") {
+    forAll { (i: Instant) =>
+      val ts = Timestamp(i.getEpochSecond, i.getNano)
+      val formatted = ts.conciseDateTime
+      val expected = conciseDateTimeFormatter.format(i)
+      expect.same(formatted, expected)
+    }
+  }
 }