diff --git a/centaur/src/main/resources/standardTestCases/biscayne_new_engine_functions.test b/centaur/src/main/resources/standardTestCases/biscayne_new_engine_functions.test
index 6998d4af7e7..e05af2f8a2d 100644
--- a/centaur/src/main/resources/standardTestCases/biscayne_new_engine_functions.test
+++ b/centaur/src/main/resources/standardTestCases/biscayne_new_engine_functions.test
@@ -55,6 +55,8 @@ metadata {
   "outputs.biscayne_new_engine_functions.minMaxIntFloatComposition": 1.0
   "outputs.biscayne_new_engine_functions.maxIntVsMaxFloat": 1.79769313E+308
 
+  "outputs.biscayne_new_engine_functions.substituted": "WATtheWAT"
+
   "outputs.biscayne_new_engine_functions.with_suffixes.0": "aaaS"
   "outputs.biscayne_new_engine_functions.with_suffixes.1": "bbbS"
   "outputs.biscayne_new_engine_functions.with_suffixes.2": "cccS"
diff --git a/centaur/src/main/resources/standardTestCases/wdl_biscayne/biscayne_new_engine_functions/biscayne_new_engine_functions.wdl b/centaur/src/main/resources/standardTestCases/wdl_biscayne/biscayne_new_engine_functions/biscayne_new_engine_functions.wdl
index f7b3d0de7fd..c4387134421 100644
--- a/centaur/src/main/resources/standardTestCases/wdl_biscayne/biscayne_new_engine_functions/biscayne_new_engine_functions.wdl
+++ b/centaur/src/main/resources/standardTestCases/wdl_biscayne/biscayne_new_engine_functions/biscayne_new_engine_functions.wdl
@@ -4,7 +4,7 @@ workflow biscayne_new_engine_functions {
 
   meta {
     description: "This test makes sure that these functions work in a real workflow"
-    functions_under_test: [ "keys", "as_map", "as_pairs", "collect_by_key", "suffix" ]
+    functions_under_test: [ "keys", "as_map", "as_pairs", "collect_by_key", "sub", "suffix" ]
   }
 
   Map[String, Int] x_map_in = {"a": 1, "b": 2, "c": 3}
@@ -51,6 +51,11 @@ workflow biscayne_new_engine_functions {
     Float minMaxIntFloatComposition = min(max(biggestInt, smallFloat), smallestInt) # 1.0
     Float maxIntVsMaxFloat = max(maxInt, maxFloat)
 
+    # sub():
+    # (Exists before Biscayne, but uses different regex flavor here)
+    # =================================================
+    String substituted = sub("AtheZ", "[[:upper:]]", "WAT")
+
     # suffix():
     # =================================================
     Array[String] with_suffixes = suffix("S", some_strings)
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 6b1e3cc1740..30396519016 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -103,6 +103,7 @@ object Dependencies {
   private val postgresV = "42.4.4"
   private val pprintV = "0.7.3"
   private val rdf4jV = "3.7.1"
+  private val re2jV = "1.6"
   private val refinedV = "0.10.1"
   private val rhinoV = "1.7.14"
 
@@ -517,7 +518,8 @@ object Dependencies {
   val wdlDependencies: List[ModuleID] = List(
     "commons-io" % "commons-io" % commonsIoV,
     "org.scala-graph" %% "graph-core" % scalaGraphV,
-    "com.chuusai" %% "shapeless" % shapelessV
+    "com.chuusai" %% "shapeless" % shapelessV,
+    "com.google.re2j" % "re2j" % re2jV,
   ) ++ betterFilesDependencies
 
   val languageFactoryDependencies = List(
diff --git a/wdl/model/draft3/src/main/scala/wdl/model/draft3/elements/ExpressionElement.scala b/wdl/model/draft3/src/main/scala/wdl/model/draft3/elements/ExpressionElement.scala
index 91f34d064ae..23101adfa9e 100644
--- a/wdl/model/draft3/src/main/scala/wdl/model/draft3/elements/ExpressionElement.scala
+++ b/wdl/model/draft3/src/main/scala/wdl/model/draft3/elements/ExpressionElement.scala
@@ -180,6 +180,8 @@ object ExpressionElement {
     def arg2: ExpressionElement
     def arg3: ExpressionElement
   }
+
+  // Pre-1.1 WDL versions have undefined regex flavor. Cromwell uses the standard Java flavor.
   final case class Sub(input: ExpressionElement, pattern: ExpressionElement, replace: ExpressionElement)
       extends ThreeParamFunctionCallElement {
     override def arg1: ExpressionElement = input
@@ -187,6 +189,14 @@ object ExpressionElement {
     override def arg3: ExpressionElement = replace
   }
 
+  // As of WDL 1.1, WDL regular expressions are expected to be POSIX ERE flavor.
+  final case class SubPosix(input: ExpressionElement, pattern: ExpressionElement, replace: ExpressionElement)
+      extends ThreeParamFunctionCallElement {
+    override def arg1: ExpressionElement = input
+    override def arg2: ExpressionElement = pattern
+    override def arg3: ExpressionElement = replace
+  }
+
   /**
     * A single identifier lookup expression, eg Int x = y
     */
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/ast2wdlom/AstToNewExpressionElements.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/ast2wdlom/AstToNewExpressionElements.scala
index 5c0c01859c2..70ebd4879c3 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/ast2wdlom/AstToNewExpressionElements.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/ast2wdlom/AstToNewExpressionElements.scala
@@ -3,7 +3,7 @@ package wdl.transforms.biscayne.ast2wdlom
 import cats.syntax.validated._
 import common.validation.ErrorOr.ErrorOr
 import wdl.model.draft3.elements.ExpressionElement
-import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, Suffix}
+import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, SubPosix, Suffix}
 import wdl.transforms.base.ast2wdlom.AstNodeToExpressionElement
 
 object AstToNewExpressionElements {
@@ -15,6 +15,7 @@ object AstToNewExpressionElements {
     "min" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Min, "min"),
     "max" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Max, "max"),
     "sep" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Sep, "sep"),
+    "sub" -> AstNodeToExpressionElement.validateThreeParamEngineFunction(SubPosix, "sub"),
     "suffix" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Suffix, "suffix"),
     "read_object" -> (_ =>
       "read_object is no longer available in this WDL version. Consider using read_json instead".invalidNel
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumers.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumers.scala
index 3c73f8b55cd..8c5e200e7ee 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumers.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumers.scala
@@ -58,6 +58,16 @@ object BiscayneExpressionValueConsumers {
         expressionValueConsumer.expressionConsumedValueHooks(a.arg2)(expressionValueConsumer)
   }
 
+  implicit val subPosixExpressionValueConsumer: ExpressionValueConsumer[SubPosix] =
+    new ExpressionValueConsumer[SubPosix] {
+      override def expressionConsumedValueHooks(a: SubPosix)(implicit
+        expressionValueConsumer: ExpressionValueConsumer[ExpressionElement]
+      ): Set[UnlinkedConsumedValueHook] =
+        expressionValueConsumer.expressionConsumedValueHooks(a.arg1)(expressionValueConsumer) ++
+          expressionValueConsumer.expressionConsumedValueHooks(a.arg2)(expressionValueConsumer) ++
+          expressionValueConsumer.expressionConsumedValueHooks(a.arg3)(expressionValueConsumer)
+    }
+
   implicit val suffixExpressionValueConsumer: ExpressionValueConsumer[Suffix] = new ExpressionValueConsumer[Suffix] {
     override def expressionConsumedValueHooks(a: Suffix)(implicit
       expressionValueConsumer: ExpressionValueConsumer[ExpressionElement]
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/consumed.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/consumed.scala
index e1121e1d549..0016b0c7458 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/consumed.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/consumed/consumed.scala
@@ -96,7 +96,7 @@ package object consumed {
         case a: Zip => a.expressionConsumedValueHooks(expressionValueConsumer)
         case a: Cross => a.expressionConsumedValueHooks(expressionValueConsumer)
 
-        case a: Sub => a.expressionConsumedValueHooks(expressionValueConsumer)
+        case a: SubPosix => a.expressionConsumedValueHooks(expressionValueConsumer)
 
         // New WDL biscayne expressions:
         case a: Keys => a.expressionConsumedValueHooks(expressionValueConsumer)
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluators.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluators.scala
index 6a79d2b3948..6d83600ea2b 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluators.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluators.scala
@@ -1,9 +1,12 @@
 package wdl.transforms.biscayne.linking.expression.files
 
-import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, Suffix}
+import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, SubPosix, Suffix}
 import wdl.model.draft3.graph.expression.FileEvaluator
 import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators
-import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators.twoParameterFunctionPassthroughFileEvaluator
+import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators.{
+  threeParameterFunctionPassthroughFileEvaluator,
+  twoParameterFunctionPassthroughFileEvaluator
+}
 
 object BiscayneFileEvaluators {
 
@@ -16,6 +19,8 @@ object BiscayneFileEvaluators {
     EngineFunctionEvaluators.singleParameterPassthroughFileEvaluator
 
   implicit val sepFunctionEvaluator: FileEvaluator[Sep] = twoParameterFunctionPassthroughFileEvaluator[Sep]
+  implicit val subPosixFunctionEvaluator: FileEvaluator[SubPosix] =
+    threeParameterFunctionPassthroughFileEvaluator[SubPosix]
   implicit val suffixFunctionEvaluator: FileEvaluator[Suffix] = twoParameterFunctionPassthroughFileEvaluator[Suffix]
 
   implicit val minFunctionEvaluator: FileEvaluator[Min] = twoParameterFunctionPassthroughFileEvaluator[Min]
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/files.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/files.scala
index 9dd95e9a0ec..e8a8a195289 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/files.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/files/files.scala
@@ -154,7 +154,8 @@ package object files {
         case a: Zip => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
         case a: Cross => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
 
-        case a: Sub => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
+        case a: SubPosix =>
+          a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
 
         case a: Keys => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
         case a: AsMap => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluators.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluators.scala
index 1ff5bf71ba4..73e01576abe 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluators.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluators.scala
@@ -1,6 +1,6 @@
 package wdl.transforms.biscayne.linking.expression.types
 
-import cats.implicits.catsSyntaxTuple2Semigroupal
+import cats.implicits.{catsSyntaxTuple2Semigroupal, catsSyntaxTuple3Semigroupal}
 import cats.syntax.validated._
 import common.validation.ErrorOr._
 import wdl.model.draft3.elements.ExpressionElement
@@ -102,6 +102,16 @@ object BiscayneTypeEvaluators {
       }
   }
 
+  implicit val subPosixFunctionEvaluator: TypeEvaluator[SubPosix] = new TypeEvaluator[SubPosix] {
+    override def evaluateType(a: SubPosix, linkedValues: Map[UnlinkedConsumedValueHook, GeneratedValueHandle])(implicit
+      expressionTypeEvaluator: TypeEvaluator[ExpressionElement]
+    ): ErrorOr[WomType] =
+      (validateParamType(a.input, linkedValues, WomSingleFileType),
+       validateParamType(a.pattern, linkedValues, WomSingleFileType),
+       validateParamType(a.replace, linkedValues, WomSingleFileType)
+      ) mapN { (_, _, _) => WomStringType }
+  }
+
   implicit val suffixFunctionEvaluator: TypeEvaluator[Suffix] = new TypeEvaluator[Suffix] {
     override def evaluateType(a: Suffix, linkedValues: Map[UnlinkedConsumedValueHook, GeneratedValueHandle])(implicit
       expressionTypeEvaluator: TypeEvaluator[ExpressionElement]
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/types.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/types.scala
index dec2deeb24f..fbcfcd6d339 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/types.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/types/types.scala
@@ -98,7 +98,7 @@ package object types {
         case a: Zip => a.evaluateType(linkedValues)(typeEvaluator)
         case a: Cross => a.evaluateType(linkedValues)(typeEvaluator)
 
-        case a: Sub => a.evaluateType(linkedValues)(typeEvaluator)
+        case a: SubPosix => a.evaluateType(linkedValues)(typeEvaluator)
 
         case a: StdoutElement.type => a.evaluateType(linkedValues)(typeEvaluator)
         case a: StderrElement.type => a.evaluateType(linkedValues)(typeEvaluator)
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluators.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluators.scala
index 0c4805f0e68..0e29f40b2fd 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluators.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluators.scala
@@ -4,12 +4,15 @@ import cats.data.NonEmptyList
 import cats.syntax.validated._
 import cats.syntax.traverse._
 import cats.instances.list._
+import com.google.re2j.{Pattern => RE2JPattern}
 import common.validation.ErrorOr._
 import common.collections.EnhancedCollections._
+import common.validation.ErrorOr
 import wdl.model.draft3.elements.ExpressionElement
 import wdl.model.draft3.elements.ExpressionElement._
 import wdl.model.draft3.graph.expression.{EvaluatedValue, ForCommandInstantiationOptions, ValueEvaluator}
 import wdl.transforms.base.linking.expression.values.EngineFunctionEvaluators.{
+  processThreeValidatedValues,
   processTwoValidatedValues,
   processValidatedSingleValue
 }
@@ -218,6 +221,36 @@ object BiscayneValueEvaluators {
       }
   }
 
+  implicit val subPosixFunctionEvaluator: ValueEvaluator[SubPosix] = new ValueEvaluator[SubPosix] {
+    override def evaluateValue(a: SubPosix,
+                               inputs: Map[String, WomValue],
+                               ioFunctionSet: IoFunctionSet,
+                               forCommandInstantiationOptions: Option[ForCommandInstantiationOptions]
+    )(implicit expressionValueEvaluator: ValueEvaluator[ExpressionElement]): ErrorOr[EvaluatedValue[WomString]] =
+      processThreeValidatedValues[WomString, WomString, WomString, WomString](
+        expressionValueEvaluator.evaluateValue(a.input, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        ),
+        expressionValueEvaluator.evaluateValue(a.pattern, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        ),
+        expressionValueEvaluator.evaluateValue(a.replace, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        )
+      ) { (input, pattern, replace) =>
+        ErrorOr(
+          EvaluatedValue(WomString(
+                           RE2JPattern
+                             .compile(pattern.valueString)
+                             .matcher(input.valueString)
+                             .replaceAll(replace.valueString)
+                         ),
+                         Seq.empty
+          )
+        )
+      }
+  }
+
   implicit val suffixFunctionEvaluator: ValueEvaluator[Suffix] = new ValueEvaluator[Suffix] {
     override def evaluateValue(a: Suffix,
                                inputs: Map[String, WomValue],
diff --git a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/values.scala b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/values.scala
index 3106ceba428..3a3ba825fe9 100644
--- a/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/values.scala
+++ b/wdl/transforms/biscayne/src/main/scala/wdl/transforms/biscayne/linking/expression/values/values.scala
@@ -165,7 +165,8 @@ package object values {
         case a: Cross =>
           a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
 
-        case a: Sub => a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
+        case a: SubPosix =>
+          a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
 
         case a: Keys => a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
         case a: AsMap =>
diff --git a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/Ast2WdlomSpec.scala b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/Ast2WdlomSpec.scala
index a0953cd8397..b3a28b0d203 100644
--- a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/Ast2WdlomSpec.scala
+++ b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/Ast2WdlomSpec.scala
@@ -1,7 +1,6 @@
 package wdl.transforms.biscayne
 
 import java.util
-
 import common.Checked
 import common.assertion.ErrorOrAssertions._
 import common.transforms.CheckedAtoB
@@ -98,6 +97,12 @@ class Ast2WdlomSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
     expr shouldBeValid NoneLiteralElement
   }
 
+  it should "get the posix version when parsing the sub function" in {
+    val str = """sub("my input", "[A-Za-z]", "repl")"""
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+    expr shouldBeValid (SubPosix(StringLiteral("my input"), StringLiteral("[A-Za-z]"), StringLiteral("repl")))
+  }
+
   it should "parse the new suffix function" in {
     val str = "suffix(some_str, some_arr)"
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumersSpec.scala b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumersSpec.scala
index 76f4a0338e7..841f283a512 100644
--- a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumersSpec.scala
+++ b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/consumed/BiscayneExpressionValueConsumersSpec.scala
@@ -58,6 +58,15 @@ class BiscayneExpressionValueConsumersSpec extends AnyFlatSpec with CromwellTime
     }
   }
 
+  it should "discover the variable lookups within a sub() call" in {
+    val str = """ sub(my_input, "^[A-Z]$", "0") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.expressionConsumedValueHooks should be(Set(UnlinkedIdentifierHook("my_input")))
+    }
+  }
+
   it should "discover the variable lookups within a suffix() call" in {
     val str = """ suffix(my_suffix, ["a", "b", c]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluatorSpec.scala b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluatorSpec.scala
index 4a3ed6b63b9..11affe50c66 100644
--- a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluatorSpec.scala
+++ b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/files/BiscayneFileEvaluatorSpec.scala
@@ -46,6 +46,17 @@ class BiscayneFileEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wit
     }
   }
 
+  it should "discover the file which would be required to evaluate a sub() function" in {
+    val str = """ sub(read_string("my_nice_file.txt"), "foo", "NEW_VAL") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.predictFilesNeededToEvaluate(Map.empty, NoIoFunctionSet, WomStringType) shouldBeValid Set(
+        WomSingleFile("my_nice_file.txt")
+      )
+    }
+  }
+
   it should "discover the file which would be required to evaluate a suffix() function" in {
     val str = """ suffix(' # what a line', read_lines("foo.txt")) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluatorSpec.scala b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluatorSpec.scala
index c8372d36cd1..bea86f6d850 100644
--- a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluatorSpec.scala
+++ b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/types/BiscayneTypeEvaluatorSpec.scala
@@ -56,6 +56,15 @@ class BiscayneTypeEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wit
     }
   }
 
+  it should "evaluate the type of a sub() function as String" in {
+    val str = """ sub("input", "^pattern$", "s") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateType(Map.empty) shouldBeValid WomStringType
+    }
+  }
+
   it should "evaluate the type of a suffix() function as Array[String]" in {
     val str = """ suffix('S', ["a", "b", "c"]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluatorSpec.scala b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluatorSpec.scala
index 1487543a838..66d07e02fe4 100644
--- a/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluatorSpec.scala
+++ b/wdl/transforms/biscayne/src/test/scala/wdl/transforms/biscayne/linking/expression/values/BiscayneValueEvaluatorSpec.scala
@@ -201,6 +201,29 @@ class BiscayneValueEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wi
     }
   }
 
+  it should "evaluate a POSIX-flavor regex in a sub expression correctly" in {
+    val str = """ sub("aB", "[[:lower:]]", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    val expectedString: WomString = WomString("9B")
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None) shouldBeValid EvaluatedValue(expectedString, Seq.empty)
+    }
+  }
+
+  it should "fail to evaluate a Java-flavor regex in a sub expression" in {
+    val str = """ sub("aB", "\\p{Lower}", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None)
+        .shouldBeInvalid(
+          """error parsing regexp: invalid character class range: `\p{Lower}`"""
+        )
+    }
+  }
+
   it should "evaluate a suffix expression correctly" in {
     val str = """ suffix("S", ["a", "b", "c"]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/ast2wdlom/AstToNewExpressionElements.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/ast2wdlom/AstToNewExpressionElements.scala
index 46cd8cb2e60..c1f36aae542 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/ast2wdlom/AstToNewExpressionElements.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/ast2wdlom/AstToNewExpressionElements.scala
@@ -3,7 +3,7 @@ package wdl.transforms.cascades.ast2wdlom
 import cats.syntax.validated._
 import common.validation.ErrorOr.ErrorOr
 import wdl.model.draft3.elements.ExpressionElement
-import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, Suffix}
+import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, SubPosix, Suffix}
 import wdl.transforms.base.ast2wdlom.AstNodeToExpressionElement
 
 object AstToNewExpressionElements {
@@ -15,6 +15,7 @@ object AstToNewExpressionElements {
     "min" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Min, "min"),
     "max" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Max, "max"),
     "sep" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Sep, "sep"),
+    "sub" -> AstNodeToExpressionElement.validateThreeParamEngineFunction(SubPosix, "sub"),
     "suffix" -> AstNodeToExpressionElement.validateTwoParamEngineFunction(Suffix, "suffix"),
     "read_object" -> (_ =>
       "read_object is no longer available in this WDL version. Consider using read_json instead".invalidNel
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumers.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumers.scala
index ebc6d48fba1..332550dde47 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumers.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumers.scala
@@ -58,6 +58,16 @@ object cascadesExpressionValueConsumers {
         expressionValueConsumer.expressionConsumedValueHooks(a.arg2)(expressionValueConsumer)
   }
 
+  implicit val subPosixExpressionValueConsumer: ExpressionValueConsumer[SubPosix] =
+    new ExpressionValueConsumer[SubPosix] {
+      override def expressionConsumedValueHooks(a: SubPosix)(implicit
+        expressionValueConsumer: ExpressionValueConsumer[ExpressionElement]
+      ): Set[UnlinkedConsumedValueHook] =
+        expressionValueConsumer.expressionConsumedValueHooks(a.arg1)(expressionValueConsumer) ++
+          expressionValueConsumer.expressionConsumedValueHooks(a.arg2)(expressionValueConsumer) ++
+          expressionValueConsumer.expressionConsumedValueHooks(a.arg3)(expressionValueConsumer)
+    }
+
   implicit val suffixExpressionValueConsumer: ExpressionValueConsumer[Suffix] = new ExpressionValueConsumer[Suffix] {
     override def expressionConsumedValueHooks(a: Suffix)(implicit
       expressionValueConsumer: ExpressionValueConsumer[ExpressionElement]
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/consumed.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/consumed.scala
index 2026aaec010..fa6df7e9c97 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/consumed.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/consumed/consumed.scala
@@ -96,7 +96,7 @@ package object consumed {
         case a: Zip => a.expressionConsumedValueHooks(expressionValueConsumer)
         case a: Cross => a.expressionConsumedValueHooks(expressionValueConsumer)
 
-        case a: Sub => a.expressionConsumedValueHooks(expressionValueConsumer)
+        case a: SubPosix => a.expressionConsumedValueHooks(expressionValueConsumer)
 
         // New WDL biscayne expressions:
         case a: Keys => a.expressionConsumedValueHooks(expressionValueConsumer)
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluators.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluators.scala
index 32ea447b584..f551359f215 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluators.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluators.scala
@@ -1,9 +1,12 @@
 package wdl.transforms.cascades.linking.expression.files
 
-import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, Suffix}
+import wdl.model.draft3.elements.ExpressionElement.{AsMap, AsPairs, CollectByKey, Keys, Max, Min, Sep, SubPosix, Suffix}
 import wdl.model.draft3.graph.expression.FileEvaluator
 import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators
-import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators.twoParameterFunctionPassthroughFileEvaluator
+import wdl.transforms.base.linking.expression.files.EngineFunctionEvaluators.{
+  threeParameterFunctionPassthroughFileEvaluator,
+  twoParameterFunctionPassthroughFileEvaluator
+}
 
 object cascadesFileEvaluators {
 
@@ -16,6 +19,8 @@ object cascadesFileEvaluators {
     EngineFunctionEvaluators.singleParameterPassthroughFileEvaluator
 
   implicit val sepFunctionEvaluator: FileEvaluator[Sep] = twoParameterFunctionPassthroughFileEvaluator[Sep]
+  implicit val subPosixFunctionEvaluator: FileEvaluator[SubPosix] =
+    threeParameterFunctionPassthroughFileEvaluator[SubPosix]
   implicit val suffixFunctionEvaluator: FileEvaluator[Suffix] = twoParameterFunctionPassthroughFileEvaluator[Suffix]
 
   implicit val minFunctionEvaluator: FileEvaluator[Min] = twoParameterFunctionPassthroughFileEvaluator[Min]
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/files.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/files.scala
index a53c85b9b89..f075f82a4ff 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/files.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/files/files.scala
@@ -154,7 +154,8 @@ package object files {
         case a: Zip => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
         case a: Cross => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
 
-        case a: Sub => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
+        case a: SubPosix =>
+          a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
 
         case a: Keys => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
         case a: AsMap => a.predictFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)(fileEvaluator, valueEvaluator)
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluators.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluators.scala
index 180af9eb0d8..7b1b2e45dc5 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluators.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluators.scala
@@ -1,6 +1,6 @@
 package wdl.transforms.biscayne.linking.expression.types
 
-import cats.implicits.catsSyntaxTuple2Semigroupal
+import cats.implicits.{catsSyntaxTuple2Semigroupal, catsSyntaxTuple3Semigroupal}
 import cats.syntax.validated._
 import common.validation.ErrorOr._
 import wdl.model.draft3.elements.ExpressionElement
@@ -102,6 +102,16 @@ object cascadesTypeEvaluators {
       }
   }
 
+  implicit val subPosixFunctionEvaluator: TypeEvaluator[SubPosix] = new TypeEvaluator[SubPosix] {
+    override def evaluateType(a: SubPosix, linkedValues: Map[UnlinkedConsumedValueHook, GeneratedValueHandle])(implicit
+      expressionTypeEvaluator: TypeEvaluator[ExpressionElement]
+    ): ErrorOr[WomType] =
+      (validateParamType(a.input, linkedValues, WomSingleFileType),
+       validateParamType(a.pattern, linkedValues, WomSingleFileType),
+       validateParamType(a.replace, linkedValues, WomSingleFileType)
+      ) mapN { (_, _, _) => WomStringType }
+  }
+
   implicit val suffixFunctionEvaluator: TypeEvaluator[Suffix] = new TypeEvaluator[Suffix] {
     override def evaluateType(a: Suffix, linkedValues: Map[UnlinkedConsumedValueHook, GeneratedValueHandle])(implicit
       expressionTypeEvaluator: TypeEvaluator[ExpressionElement]
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/types.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/types.scala
index 4dd7c528e8b..70cc81ee395 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/types.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/types/types.scala
@@ -98,7 +98,7 @@ package object types {
         case a: Zip => a.evaluateType(linkedValues)(typeEvaluator)
         case a: Cross => a.evaluateType(linkedValues)(typeEvaluator)
 
-        case a: Sub => a.evaluateType(linkedValues)(typeEvaluator)
+        case a: SubPosix => a.evaluateType(linkedValues)(typeEvaluator)
 
         case a: StdoutElement.type => a.evaluateType(linkedValues)(typeEvaluator)
         case a: StderrElement.type => a.evaluateType(linkedValues)(typeEvaluator)
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluators.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluators.scala
index db9df85bf06..7489728980e 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluators.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluators.scala
@@ -4,12 +4,15 @@ import cats.data.NonEmptyList
 import cats.syntax.validated._
 import cats.syntax.traverse._
 import cats.instances.list._
+import com.google.re2j.{Pattern => RE2JPattern}
 import common.validation.ErrorOr._
 import common.collections.EnhancedCollections._
+import common.validation.ErrorOr
 import wdl.model.draft3.elements.ExpressionElement
 import wdl.model.draft3.elements.ExpressionElement._
 import wdl.model.draft3.graph.expression.{EvaluatedValue, ForCommandInstantiationOptions, ValueEvaluator}
 import wdl.transforms.base.linking.expression.values.EngineFunctionEvaluators.{
+  processThreeValidatedValues,
   processTwoValidatedValues,
   processValidatedSingleValue
 }
@@ -218,6 +221,36 @@ object cascadesValueEvaluators {
       }
   }
 
+  implicit val subPosixFunctionEvaluator: ValueEvaluator[SubPosix] = new ValueEvaluator[SubPosix] {
+    override def evaluateValue(a: SubPosix,
+                               inputs: Map[String, WomValue],
+                               ioFunctionSet: IoFunctionSet,
+                               forCommandInstantiationOptions: Option[ForCommandInstantiationOptions]
+    )(implicit expressionValueEvaluator: ValueEvaluator[ExpressionElement]): ErrorOr[EvaluatedValue[WomString]] =
+      processThreeValidatedValues[WomString, WomString, WomString, WomString](
+        expressionValueEvaluator.evaluateValue(a.input, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        ),
+        expressionValueEvaluator.evaluateValue(a.pattern, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        ),
+        expressionValueEvaluator.evaluateValue(a.replace, inputs, ioFunctionSet, forCommandInstantiationOptions)(
+          expressionValueEvaluator
+        )
+      ) { (input, pattern, replace) =>
+        ErrorOr(
+          EvaluatedValue(WomString(
+                           RE2JPattern
+                             .compile(pattern.valueString)
+                             .matcher(input.valueString)
+                             .replaceAll(replace.valueString)
+                         ),
+                         Seq.empty
+          )
+        )
+      }
+  }
+
   implicit val suffixFunctionEvaluator: ValueEvaluator[Suffix] = new ValueEvaluator[Suffix] {
     override def evaluateValue(a: Suffix,
                                inputs: Map[String, WomValue],
diff --git a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/values.scala b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/values.scala
index 8850d4371df..d0e2fb8c155 100644
--- a/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/values.scala
+++ b/wdl/transforms/cascades/src/main/scala/wdl/transforms/cascades/linking/expression/values/values.scala
@@ -165,7 +165,8 @@ package object values {
         case a: Cross =>
           a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
 
-        case a: Sub => a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
+        case a: SubPosix =>
+          a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
 
         case a: Keys => a.evaluateValue(inputs, ioFunctionSet, forCommandInstantiationOptions)(expressionValueEvaluator)
         case a: AsMap =>
diff --git a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumersSpec.scala b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumersSpec.scala
index 57beb7a12a1..49602617a42 100644
--- a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumersSpec.scala
+++ b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/consumed/CascadesExpressionValueConsumersSpec.scala
@@ -58,6 +58,15 @@ class CascadesExpressionValueConsumersSpec extends AnyFlatSpec with CromwellTime
     }
   }
 
+  it should "discover the variable lookups within a sub() call" in {
+    val str = """ sub(my_input, "^[A-Z]$", "0") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.expressionConsumedValueHooks should be(Set(UnlinkedIdentifierHook("my_input")))
+    }
+  }
+
   it should "discover the variable lookups within a suffix() call" in {
     val str = """ suffix(my_suffix, ["a", "b", c]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluatorSpec.scala b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluatorSpec.scala
index 5335f7d5f29..1733630c121 100644
--- a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluatorSpec.scala
+++ b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/files/CascadesFileEvaluatorSpec.scala
@@ -46,6 +46,17 @@ class CascadesFileEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wit
     }
   }
 
+  it should "discover the file which would be required to evaluate a sub() function" in {
+    val str = """ sub(read_string("my_nice_file.txt"), "foo", "NEW_VAL") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.predictFilesNeededToEvaluate(Map.empty, NoIoFunctionSet, WomStringType) shouldBeValid Set(
+        WomSingleFile("my_nice_file.txt")
+      )
+    }
+  }
+
   it should "discover the file which would be required to evaluate a suffix() function" in {
     val str = """ suffix(' # what a line', read_lines("foo.txt")) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluatorSpec.scala b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluatorSpec.scala
index 954ef0f52f0..a84adccfa0f 100644
--- a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluatorSpec.scala
+++ b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/types/CascadesTypeEvaluatorSpec.scala
@@ -56,6 +56,15 @@ class CascadesTypeEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wit
     }
   }
 
+  it should "evaluate the type of a sub() function as String" in {
+    val str = """ sub("input", "^pattern$", "s") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateType(Map.empty) shouldBeValid WomStringType
+    }
+  }
+
   it should "evaluate the type of a suffix() function as Array[String]" in {
     val str = """ suffix('S', ["a", "b", "c"]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluatorSpec.scala b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluatorSpec.scala
index bd47a20ca68..06ab5818331 100644
--- a/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluatorSpec.scala
+++ b/wdl/transforms/cascades/src/test/scala/wdl/transforms/cascades/linking/expression/values/CascadesValueEvaluatorSpec.scala
@@ -201,6 +201,29 @@ class CascadesValueEvaluatorSpec extends AnyFlatSpec with CromwellTimeoutSpec wi
     }
   }
 
+  it should "evaluate a POSIX-flavor regex in a sub expression correctly" in {
+    val str = """ sub("aB", "[[:lower:]]", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    val expectedString: WomString = WomString("9B")
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None) shouldBeValid EvaluatedValue(expectedString, Seq.empty)
+    }
+  }
+
+  it should "fail to evaluate a Java-flavor regex in a sub expression" in {
+    val str = """ sub("aB", "\\p{Lower}", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None)
+        .shouldBeInvalid(
+          """error parsing regexp: invalid character class range: `\p{Lower}`"""
+        )
+    }
+  }
+
   it should "evaluate a suffix expression correctly" in {
     val str = """ suffix("S", ["a", "b", "c"]) """
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/ast2wdlom/Ast2WdlomSpec.scala b/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/ast2wdlom/Ast2WdlomSpec.scala
index 664696ee86d..d99d3493b60 100644
--- a/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/ast2wdlom/Ast2WdlomSpec.scala
+++ b/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/ast2wdlom/Ast2WdlomSpec.scala
@@ -1,8 +1,8 @@
 package wdl.draft3.transforms.ast2wdlom
 
 import cats.instances.either._
-import java.util
 
+import java.util
 import common.Checked
 import common.assertion.CromwellTimeoutSpec
 import common.assertion.ErrorOrAssertions._
@@ -11,14 +11,15 @@ import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers
 import wdl.draft3.parser.WdlParser
 import wdl.draft3.parser.WdlParser.{ParseTree, SyntaxErrorFormatter}
+import wdl.draft3.transforms.ast2wdlom.Ast2WdlomSpec.{fromString, parser}
 import wdl.draft3.transforms.parsing.WdlDraft3SyntaxErrorFormatter
-import wdl.model.draft3.elements.ExpressionElement.IdentifierLookup
+import wdl.model.draft3.elements.ExpressionElement.{IdentifierLookup, StringLiteral, Sub}
 import wdl.model.draft3.elements._
 import wdl.transforms.base.ast2wdlom.GenericAstNode
 
 import scala.jdk.CollectionConverters._
 
-class Ast2WdlomSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
+object Ast2WdlomSpec {
 
   val parser = new WdlParser()
 
@@ -29,10 +30,15 @@ class Ast2WdlomSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
     val versionedExpression = "version 1.0\n" + expression
     // That "version 1.0" means we'll have 2 unwanted tokens at the start of the list, so drop 'em:
     val tokens = parser.lex(versionedExpression, "string").asScala.drop(2).asJava
-    val terminalMap = (tokens.asScala.toVector map { (_, expression) }).toMap
+    val terminalMap = (tokens.asScala.toVector map {
+      (_, expression)
+    }).toMap
     val parseTree = parseFunction(tokens, WdlDraft3SyntaxErrorFormatter(terminalMap))
     (wrapAstNode andThen converter).run(parseTree.toAst)
   }
+}
+
+class Ast2WdlomSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
 
   it should "not parse the new as_map function" in {
     val str = "as_map(some_pairs)"
@@ -52,6 +58,12 @@ class Ast2WdlomSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
     expr shouldBeInvalid "Failed to parse expression (reason 1 of 1): Unknown engine function: 'collect_by_key'"
   }
 
+  it should "get the non-posix version when parsing the sub function" in {
+    val str = """sub("my input", "[A-Za-z]", "repl")"""
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+    expr shouldBeValid (Sub(StringLiteral("my input"), StringLiteral("[A-Za-z]"), StringLiteral("repl")))
+  }
+
   it should "not parse the new suffix function" in {
     val str = "suffix(aStr, anArray)"
     val expr = fromString[ExpressionElement](str, parser.parse_e)
diff --git a/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/linking/expression/values/ValueEvaluatorsSpec.scala b/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/linking/expression/values/ValueEvaluatorsSpec.scala
new file mode 100644
index 00000000000..013a45308e6
--- /dev/null
+++ b/wdl/transforms/draft3/src/test/scala/wdl/draft3/transforms/linking/expression/values/ValueEvaluatorsSpec.scala
@@ -0,0 +1,42 @@
+package wdl.draft3.transforms.linking.expression.values
+
+import common.assertion.CromwellTimeoutSpec
+import common.assertion.ErrorOrAssertions._
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+import wdl.draft3.transforms.ast2wdlom.Ast2WdlomSpec.{fromString, parser}
+import wdl.draft3.transforms.ast2wdlom._
+import wdl.model.draft3.elements.ExpressionElement
+import wdl.model.draft3.graph.expression.EvaluatedValue
+import wdl.model.draft3.graph.expression.ValueEvaluator.ops._
+import wom.expression.NoIoFunctionSet
+import wom.values.WomString
+
+class ValueEvaluatorsSpec extends AnyFlatSpec with CromwellTimeoutSpec with Matchers {
+
+  behavior of "base value evaluator"
+
+  // In pre-1.1 WDL we use Java-flavored regex
+
+  it should "fail to apply a POSIX-flavor sub expression" in {
+    val str = """ sub("aB", "[[:lower:]]", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    val expectedString: WomString = WomString("aB") // no substitution
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None) shouldBeValid EvaluatedValue(expectedString, Seq.empty)
+    }
+  }
+
+  it should "evaluate a Java-flavor regex in a sub expression correctly" in {
+    val str = """ sub("aB", "\\p{Lower}", "9") """
+    val expr = fromString[ExpressionElement](str, parser.parse_e)
+
+    val expectedString: WomString = WomString("9B")
+
+    expr.shouldBeValidPF { case e =>
+      e.evaluateValue(Map.empty, NoIoFunctionSet, None) shouldBeValid EvaluatedValue(expectedString, Seq.empty)
+    }
+  }
+}
diff --git a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/ast2wdlom/AstNodeToExpressionElement.scala b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/ast2wdlom/AstNodeToExpressionElement.scala
index 2a773fd4e23..407d7f6f96c 100644
--- a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/ast2wdlom/AstNodeToExpressionElement.scala
+++ b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/ast2wdlom/AstNodeToExpressionElement.scala
@@ -231,7 +231,7 @@ object AstNodeToExpressionElement {
       s"Function $functionName expects exactly 2 arguments but got ${params.size}".invalidNel
     }
 
-  private def validateThreeParamEngineFunction(
+  def validateThreeParamEngineFunction(
     elementMaker: (ExpressionElement, ExpressionElement, ExpressionElement) => ExpressionElement,
     functionName: String
   )(params: Vector[ExpressionElement]): ErrorOr[ExpressionElement] =
diff --git a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/files/EngineFunctionEvaluators.scala b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/files/EngineFunctionEvaluators.scala
index 11c687588a7..b8ecf9d764b 100644
--- a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/files/EngineFunctionEvaluators.scala
+++ b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/files/EngineFunctionEvaluators.scala
@@ -219,8 +219,8 @@ object EngineFunctionEvaluators {
   implicit val crossFunctionEvaluator: FileEvaluator[Cross] = twoParameterFunctionPassthroughFileEvaluator[Cross]
   implicit val prefixFunctionEvaluator: FileEvaluator[Prefix] = twoParameterFunctionPassthroughFileEvaluator[Prefix]
 
-  implicit val subFunctionEvaluator: FileEvaluator[Sub] = new FileEvaluator[Sub] {
-    override def predictFilesNeededToEvaluate(a: Sub,
+  def threeParameterFunctionPassthroughFileEvaluator[A <: ThreeParamFunctionCallElement] = new FileEvaluator[A] {
+    override def predictFilesNeededToEvaluate(a: A,
                                               inputs: Map[String, WomValue],
                                               ioFunctionSet: IoFunctionSet,
                                               coerceTo: WomType
@@ -228,9 +228,13 @@ object EngineFunctionEvaluators {
       fileEvaluator: FileEvaluator[ExpressionElement],
       valueEvaluator: ValueEvaluator[ExpressionElement]
     ): ErrorOr[Set[WomFile]] =
-      (a.pattern.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo),
-       a.input.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo),
-       a.replace.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)
-      ) mapN { _ ++ _ ++ _ }
+      (a.arg1.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo),
+       a.arg2.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo),
+       a.arg3.evaluateFilesNeededToEvaluate(inputs, ioFunctionSet, coerceTo)
+      ) mapN {
+        _ ++ _ ++ _
+      }
   }
+
+  implicit val subFunctionEvaluator: FileEvaluator[Sub] = threeParameterFunctionPassthroughFileEvaluator[Sub]
 }
diff --git a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/values/EngineFunctionEvaluators.scala b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/values/EngineFunctionEvaluators.scala
index ffaf16ad0d2..58c83c67edc 100644
--- a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/values/EngineFunctionEvaluators.scala
+++ b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/linking/expression/values/EngineFunctionEvaluators.scala
@@ -835,7 +835,7 @@ object EngineFunctionEvaluators {
         s"Expected (${coercerA.toDisplayString}, ${coercerB.toDisplayString}) argument but got (${otherA.value.womType.stableName}, ${otherB.value.womType.stableName})".invalidNel
     }
 
-  private def processThreeValidatedValues[A <: WomValue, B <: WomValue, C <: WomValue, R <: WomValue](
+  def processThreeValidatedValues[A <: WomValue, B <: WomValue, C <: WomValue, R <: WomValue](
     arg1: ErrorOr[EvaluatedValue[_ <: WomValue]],
     arg2: ErrorOr[EvaluatedValue[_ <: WomValue]],
     arg3: ErrorOr[EvaluatedValue[_ <: WomValue]]
diff --git a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/wdlom2wdl/WdlWriterImpl.scala b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/wdlom2wdl/WdlWriterImpl.scala
index a85f3c34420..1df05e48db1 100644
--- a/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/wdlom2wdl/WdlWriterImpl.scala
+++ b/wdl/transforms/new-base/src/main/scala/wdl/transforms/base/wdlom2wdl/WdlWriterImpl.scala
@@ -401,6 +401,7 @@ object WdlWriterImpl {
       case a: OneOrTwoParamFunctionCallElement => a.toWdlV1
       case a: TwoParamFunctionCallElement => a.toWdlV1
       case a: Sub => s"sub(${a.input.toWdlV1}, ${a.pattern.toWdlV1}, ${a.replace.toWdlV1})"
+      case a: SubPosix => s"sub(${a.input.toWdlV1}, ${a.pattern.toWdlV1}, ${a.replace.toWdlV1})"
     }
   }