diff --git a/Sources/_StringProcessing/ByteCodeGen.swift b/Sources/_StringProcessing/ByteCodeGen.swift
index c44b5af94..c8cf0805c 100644
--- a/Sources/_StringProcessing/ByteCodeGen.swift
+++ b/Sources/_StringProcessing/ByteCodeGen.swift
@@ -1,4 +1,4 @@
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 extension Compiler {
   struct ByteCodeGen {
diff --git a/Sources/_StringProcessing/Capture.swift b/Sources/_StringProcessing/Capture.swift
index f7dff424e..51428acee 100644
--- a/Sources/_StringProcessing/Capture.swift
+++ b/Sources/_StringProcessing/Capture.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 /// A structured capture
 struct StructuredCapture {
diff --git a/Sources/_StringProcessing/Compiler.swift b/Sources/_StringProcessing/Compiler.swift
index 90192bdaf..96476f42b 100644
--- a/Sources/_StringProcessing/Compiler.swift
+++ b/Sources/_StringProcessing/Compiler.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 class Compiler {
   let tree: DSLTree
diff --git a/Sources/_StringProcessing/ConsumerInterface.swift b/Sources/_StringProcessing/ConsumerInterface.swift
index b49804ca1..ecb7d1356 100644
--- a/Sources/_StringProcessing/ConsumerInterface.swift
+++ b/Sources/_StringProcessing/ConsumerInterface.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 extension DSLTree.Node {
   /// Attempt to generate a consumer from this AST node
diff --git a/Sources/_StringProcessing/Engine/MEBuilder.swift b/Sources/_StringProcessing/Engine/MEBuilder.swift
index 2b849874b..7cf94f6ef 100644
--- a/Sources/_StringProcessing/Engine/MEBuilder.swift
+++ b/Sources/_StringProcessing/Engine/MEBuilder.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser // For errors
+@_implementationOnly import _RegexParser // For errors
 
 extension MEProgram where Input.Element: Hashable {
   struct Builder {
diff --git a/Sources/_StringProcessing/Engine/MECapture.swift b/Sources/_StringProcessing/Engine/MECapture.swift
index 301212736..390af7d66 100644
--- a/Sources/_StringProcessing/Engine/MECapture.swift
+++ b/Sources/_StringProcessing/Engine/MECapture.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 /*
 
diff --git a/Sources/_StringProcessing/Engine/MEProgram.swift b/Sources/_StringProcessing/Engine/MEProgram.swift
index ecd67d4ba..b0f2e6a79 100644
--- a/Sources/_StringProcessing/Engine/MEProgram.swift
+++ b/Sources/_StringProcessing/Engine/MEProgram.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 struct MEProgram<Input: Collection> where Input.Element: Equatable {
   typealias ConsumeFunction = (Input, Range<Input.Index>) -> Input.Index?
diff --git a/Sources/_StringProcessing/Engine/Registers.swift b/Sources/_StringProcessing/Engine/Registers.swift
index a2a5be104..bc17f1215 100644
--- a/Sources/_StringProcessing/Engine/Registers.swift
+++ b/Sources/_StringProcessing/Engine/Registers.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 struct SentinelValue: Hashable, CustomStringConvertible {
   var description: String { "<value sentinel>" }
diff --git a/Sources/_StringProcessing/Engine/Structuralize.swift b/Sources/_StringProcessing/Engine/Structuralize.swift
index 02a03c09c..12d2e1242 100644
--- a/Sources/_StringProcessing/Engine/Structuralize.swift
+++ b/Sources/_StringProcessing/Engine/Structuralize.swift
@@ -1,4 +1,4 @@
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 extension CaptureStructure {
   var optionalCount: Int {
diff --git a/Sources/_StringProcessing/Executor.swift b/Sources/_StringProcessing/Executor.swift
index d911c3512..c7d4527a5 100644
--- a/Sources/_StringProcessing/Executor.swift
+++ b/Sources/_StringProcessing/Executor.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 struct Executor {
   // TODO: consider let, for now lets us toggle tracing
diff --git a/Sources/_StringProcessing/MatchingOptions.swift b/Sources/_StringProcessing/MatchingOptions.swift
index 0f244f1b8..8213185c1 100644
--- a/Sources/_StringProcessing/MatchingOptions.swift
+++ b/Sources/_StringProcessing/MatchingOptions.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 /// A type that represents the current state of regex matching options, with
 /// stack-based scoping.
diff --git a/Sources/_StringProcessing/PrintAsPattern.swift b/Sources/_StringProcessing/PrintAsPattern.swift
index 8e1dd8322..edf4fad40 100644
--- a/Sources/_StringProcessing/PrintAsPattern.swift
+++ b/Sources/_StringProcessing/PrintAsPattern.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 // TODO: Add an expansion level, both from top to bottom.
 //       After `printAsCanonical` is fleshed out, these two
@@ -17,6 +17,7 @@ import _RegexParser
 //       incremental conversion, such that leaves remain
 //       as canonical regex literals.
 
+@_spi(PatternConverter)
 extension AST {
   /// Render as a Pattern DSL
   @_spi(PatternConverter)
diff --git a/Sources/_StringProcessing/Regex/ASTConversion.swift b/Sources/_StringProcessing/Regex/ASTConversion.swift
index ac88dcd73..d32770eae 100644
--- a/Sources/_StringProcessing/Regex/ASTConversion.swift
+++ b/Sources/_StringProcessing/Regex/ASTConversion.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 extension AST {
   var dslTree: DSLTree {
diff --git a/Sources/_StringProcessing/Regex/AnyRegexOutput.swift b/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
index 16829ff78..06241c7ea 100644
--- a/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
+++ b/Sources/_StringProcessing/Regex/AnyRegexOutput.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 @available(SwiftStdlib 5.7, *)
 extension Regex where Output == AnyRegexOutput {
diff --git a/Sources/_StringProcessing/Regex/Core.swift b/Sources/_StringProcessing/Regex/Core.swift
index a2cf76cd2..56a14da51 100644
--- a/Sources/_StringProcessing/Regex/Core.swift
+++ b/Sources/_StringProcessing/Regex/Core.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 
 /// A type that represents a regular expression.
diff --git a/Sources/_StringProcessing/Regex/DSLTree.swift b/Sources/_StringProcessing/Regex/DSLTree.swift
index 189b3a22d..6bf4ec47c 100644
--- a/Sources/_StringProcessing/Regex/DSLTree.swift
+++ b/Sources/_StringProcessing/Regex/DSLTree.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 @_spi(RegexBuilder)
 public struct DSLTree {
diff --git a/Sources/_StringProcessing/Regex/Options.swift b/Sources/_StringProcessing/Regex/Options.swift
index 0e30140c8..d474caae3 100644
--- a/Sources/_StringProcessing/Regex/Options.swift
+++ b/Sources/_StringProcessing/Regex/Options.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 @available(SwiftStdlib 5.7, *)
 extension RegexComponent {
diff --git a/Sources/_StringProcessing/Utility/ASTBuilder.swift b/Sources/_StringProcessing/Utility/ASTBuilder.swift
index c14454a5c..51d4f8bfc 100644
--- a/Sources/_StringProcessing/Utility/ASTBuilder.swift
+++ b/Sources/_StringProcessing/Utility/ASTBuilder.swift
@@ -25,7 +25,7 @@ AST.
 
 */
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 func alt(_ asts: [AST.Node]) -> AST.Node {
   return .alternation(
diff --git a/Sources/_StringProcessing/_CharacterClassModel.swift b/Sources/_StringProcessing/_CharacterClassModel.swift
index d160abc81..c9762f00e 100644
--- a/Sources/_StringProcessing/_CharacterClassModel.swift
+++ b/Sources/_StringProcessing/_CharacterClassModel.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _RegexParser
+@_implementationOnly import _RegexParser
 
 // NOTE: This is a model type. We want to be able to get one from
 // an AST, but this isn't a natural thing to produce in the context