diff --git a/upickle/core/src/upickle/core/Config.scala b/upickle/core/src/upickle/core/Config.scala
index afd9ceda0..e1a66f607 100644
--- a/upickle/core/src/upickle/core/Config.scala
+++ b/upickle/core/src/upickle/core/Config.scala
@@ -69,9 +69,10 @@ trait Config {
   def optionsAsNulls: Boolean = true
 
   /**
-   * Whether or not unknown keys when de-serializing case classes should be allowed.
-   * Defaults to `true`, but can be set to `false` to make the presence unknown keys
-   * raise an error
+   * Configure whether you want upickle to skip unknown keys during de-serialization
+   * of `case class`es. Can be overriden for the entire serializer via `override def`, and
+   * further overriden for individual `case class`es via the annotation
+   * `@upickle.implicits.allowUnknownKeys(b: Boolean)`
    */
   def allowUnknownKeys: Boolean = true
 }
diff --git a/upickle/implicits/src-2/upickle/implicits/internal/Macros.scala b/upickle/implicits/src-2/upickle/implicits/internal/Macros.scala
index 821ce936a..67d3942c1 100644
--- a/upickle/implicits/src-2/upickle/implicits/internal/Macros.scala
+++ b/upickle/implicits/src-2/upickle/implicits/internal/Macros.scala
@@ -192,6 +192,7 @@ object Macros {
               wrapCaseN(
                 companion,
                 rawArgs,
+                argSyms,
                 mappedArgs,
                 argSyms.map(_.typeSignature).map(func),
                 hasDefaults,
@@ -255,11 +256,18 @@ object Macros {
           .flatMap(_.scalaArgs.headOption)
           .map{case Literal(Constant(s)) => s.toString}
     }
+    def serializeDefaults(sym: c.Symbol): Option[Boolean] = {
+        sym.annotations
+          .find(_.tpe == typeOf[upickle.implicits.serializeDefaults])
+          .flatMap(_.scalaArgs.headOption)
+          .map{case Literal(Constant(s)) => s.asInstanceOf[Boolean]}
+    }
 
     def wrapObject(obj: Tree): Tree
 
     def wrapCaseN(companion: Tree,
                   rawArgs: Seq[String],
+                  argSyms: Seq[Symbol],
                   mappedArgs: Seq[String],
                   argTypes: Seq[Type],
                   hasDefaults: Seq[Boolean],
@@ -274,6 +282,7 @@ object Macros {
 
     def wrapCaseN(companion: c.Tree,
                   rawArgs: Seq[String],
+                  argSyms: Seq[Symbol],
                   mappedArgs: Seq[String],
                   argTypes: Seq[Type],
                   hasDefaults: Seq[Boolean],
@@ -395,13 +404,20 @@ object Macros {
     def internal = q"${c.prefix}.Internal"
     def wrapCaseN(companion: c.Tree,
                   rawArgs: Seq[String],
+                  argSyms: Seq[Symbol],
                   mappedArgs: Seq[String],
                   argTypes: Seq[Type],
                   hasDefaults: Seq[Boolean],
                   targetType: c.Type,
                   varargs: Boolean) = {
       val defaults = deriveDefaults(companion, hasDefaults)
-      val serDfltVals  = q"${c.prefix}.serializeDefaults"
+      def serDfltVals(i: Int) = {
+        val b: Option[Boolean] = serializeDefaults(argSyms(i)).orElse(serializeDefaults(targetType.typeSymbol))
+        b match {
+          case Some(b) => q"${b}"
+          case None => q"${c.prefix}.serializeDefaults"
+        }
+      }
 
       def write(i: Int) = {
         val snippet = q"""
@@ -412,9 +428,9 @@ object Macros {
              v.${TermName(rawArgs(i))}
            )
         """
-        
+
         if (!hasDefaults(i)) snippet
-        else q"""if ($serDfltVals || v.${TermName(rawArgs(i))} != ${defaults(i)}) $snippet"""
+        else q"""if (${serDfltVals(i)} || v.${TermName(rawArgs(i))} != ${defaults(i)}) $snippet"""
       }
       q"""
         new ${c.prefix}.CaseClassWriter[$targetType]{
@@ -423,7 +439,7 @@ object Macros {
               Range(0, rawArgs.length)
                 .map(i =>
                   if (!hasDefaults(i)) q"1"
-                  else q"""if ($serDfltVals || v.${TermName(rawArgs(i))} != ${defaults(i)}) 1 else 0"""
+                  else q"""if (${serDfltVals(i)} || v.${TermName(rawArgs(i))} != ${defaults(i)}) 1 else 0"""
                 )
                 .foldLeft[Tree](q"0"){case (prev, next) => q"$prev + $next"}
             }
diff --git a/upickle/implicits/src-3/upickle/implicits/macros.scala b/upickle/implicits/src-3/upickle/implicits/macros.scala
index a68e28ea3..699bfb9b6 100644
--- a/upickle/implicits/src-3/upickle/implicits/macros.scala
+++ b/upickle/implicits/src-3/upickle/implicits/macros.scala
@@ -41,6 +41,13 @@ def extractKey[A](using Quotes)(sym: quotes.reflect.Symbol): Option[String] =
     .find(_.tpe =:= TypeRepr.of[upickle.implicits.key])
     .map{case Apply(_, Literal(StringConstant(s)) :: Nil) => s}
 
+def extractSerializeDefaults[A](using quotes: Quotes)(sym: quotes.reflect.Symbol): Option[Boolean] =
+  import quotes.reflect._
+  sym
+    .annotations
+    .find(_.tpe =:= TypeRepr.of[upickle.implicits.serializeDefaults])
+    .map{case Apply(_, Literal(BooleanConstant(s)) :: Nil) => s}
+
 inline def extractIgnoreUnknownKeys[T](): List[Boolean] = ${extractIgnoreUnknownKeysImpl[T]}
 def extractIgnoreUnknownKeysImpl[T](using Quotes, Type[T]): Expr[List[Boolean]] =
   import quotes.reflect._
@@ -111,16 +118,28 @@ inline def writeLength[T](inline thisOuter: upickle.core.Types with upickle.impl
                           inline v: T): Int =
   ${writeLengthImpl[T]('thisOuter, 'v)}
 
+def serDfltVals(using quotes: Quotes)(thisOuter: Expr[upickle.core.Types with upickle.implicits.MacrosCommon],
+                                      argSym: quotes.reflect.Symbol,
+                                      targetType: quotes.reflect.Symbol): Expr[Boolean] = {
+  extractSerializeDefaults(argSym).orElse(extractSerializeDefaults(targetType)) match {
+    case Some(b) => Expr(b)
+    case None => '{ ${ thisOuter }.serializeDefaults }
+  }
+}
 def writeLengthImpl[T](thisOuter: Expr[upickle.core.Types with upickle.implicits.MacrosCommon],
                                        v: Expr[T])
-                                      (using Quotes, Type[T]): Expr[Int] =
+                                      (using quotes: Quotes, t: Type[T]): Expr[Int] =
   import quotes.reflect.*
     fieldLabelsImpl0[T]
       .map{(rawLabel, label) =>
         val defaults = getDefaultParamsImpl0[T]
         val select = Select.unique(v.asTerm, rawLabel.name).asExprOf[Any]
+
         if (!defaults.contains(label)) '{1}
-        else '{if (${thisOuter}.serializeDefaults || ${select} != ${defaults(label)}) 1 else 0}
+        else {
+          val serDflt = serDfltVals(thisOuter, rawLabel, TypeRepr.of[T].typeSymbol)
+          '{if (${serDflt} || ${select} != ${defaults(label)}) 1 else 0}
+        }
       }
       .foldLeft('{0}) { case (prev, next) => '{$prev + $next} }
 
@@ -166,7 +185,10 @@ def writeSnippetsImpl[R, T, WS <: Tuple](thisOuter: Expr[upickle.core.Types with
             )
           }
           if (!defaults.contains(label)) snippet
-          else '{if (${thisOuter}.serializeDefaults || ${select} != ${defaults(label)}) $snippet}
+          else {
+            val serDflt = serDfltVals(thisOuter, rawLabel, TypeRepr.of[T].typeSymbol)
+            '{if ($serDflt || ${select} != ${defaults(label)}) $snippet}
+          }
 
     },
     '{()}
diff --git a/upickle/implicits/src/upickle/implicits/CaseClassReadWriters.scala b/upickle/implicits/src/upickle/implicits/CaseClassReadWriters.scala
index cd1480994..a637cd170 100644
--- a/upickle/implicits/src/upickle/implicits/CaseClassReadWriters.scala
+++ b/upickle/implicits/src/upickle/implicits/CaseClassReadWriters.scala
@@ -11,7 +11,6 @@ import upickle.core.{Abort, AbortException, ArrVisitor, NoOpVisitor, ObjVisitor,
 * package to form the public API1
 */
 trait CaseClassReadWriters extends upickle.core.Types{
-  
   abstract class CaseClassReader[V] extends SimpleReader[V] {
     override def expectedMsg = "expected dictionary"
 
diff --git a/upickle/implicits/src/upickle/implicits/key.scala b/upickle/implicits/src/upickle/implicits/key.scala
index dc0efe19a..3708bae11 100644
--- a/upickle/implicits/src/upickle/implicits/key.scala
+++ b/upickle/implicits/src/upickle/implicits/key.scala
@@ -2,5 +2,30 @@ package upickle.implicits
 
 import scala.annotation.StaticAnnotation
 
+/**
+ * Annotation for control over the strings used to serialize your data structure. Can
+ * be applied in three ways:
+ *
+ * 1. To individual fields, in which case it overrides the JSON object fieldname
+ *
+ * 2. To `case class`es which are part of `sealed trait`s, where it overrides
+ *    the value of the `"$type": "foo"` discriminator field
+ *
+ * 2. To `sealed trait`s themselves, where it overrides
+ *    the key of the `"$type": "foo"` discriminator field
+ */
 class key(s: String) extends StaticAnnotation
-class allowUnknownKeys(b: Boolean) extends StaticAnnotation
\ No newline at end of file
+
+/**
+ * Annotation for fine-grained control of the `def serializeDefaults` configuration
+ * on the upickle bundle; can be applied to individual fields or to entire `case class`es,
+ * with finer-grained application taking precedence
+ */
+class serializeDefaults(s: Boolean) extends StaticAnnotation
+
+/**
+ * Annotation for fine-grained control of the `def allowUnknownKeys` configuration
+ * on the upickle bundle; can be applied to individual `case class`es, taking precedence
+ * over upickle pickler-level configuration
+ */
+class allowUnknownKeys(b: Boolean) extends StaticAnnotation
diff --git a/upickle/src/upickle/Api.scala b/upickle/src/upickle/Api.scala
index 12d39d461..4b3f066ea 100644
--- a/upickle/src/upickle/Api.scala
+++ b/upickle/src/upickle/Api.scala
@@ -170,13 +170,6 @@ trait Api
     def write0[R](out: Visitor[_, R], v: T): R = readwriter.write0(out, v)
   }
 
-  /**
-   * Configure whether you want upickle to skip unknown keys during de-serialization
-   * of `case class`es. Can be overriden for the entire serializer via `override def`, and
-   * further overriden for individual `case class`es via the annotation
-   * `@upickle.implicits.allowUnknownKeys(b: Boolean)`
-   */
-  override def allowUnknownKeys: Boolean = true
   // End Api
 }