diff --git a/Sources/AnyLanguageModel/Shared/StructuredGeneration.swift b/Sources/AnyLanguageModel/Shared/StructuredGeneration.swift
index aae832e2..eb45bd93 100644
--- a/Sources/AnyLanguageModel/Shared/StructuredGeneration.swift
+++ b/Sources/AnyLanguageModel/Shared/StructuredGeneration.swift
@@ -46,6 +46,8 @@ private final class StringTokenCache: @unchecked Sendable {
     }
 
     private let tokensByKey = Locked<[Key: Set<Int>]>([:])
+    private let integerTokensByKey = Locked<[Key: Set<Int>]>([:])
+    private let decimalTokensByKey = Locked<[Key: Set<Int>]>([:])
 
     func tokens(for key: Key) -> Set<Int>? {
         tokensByKey.withLock { $0[key] }
@@ -54,6 +56,22 @@ private final class StringTokenCache: @unchecked Sendable {
     func store(_ tokens: Set<Int>, for key: Key) {
         tokensByKey.withLock { $0[key] = tokens }
     }
+
+    func integerTokens(for key: Key) -> Set<Int>? {
+        integerTokensByKey.withLock { $0[key] }
+    }
+
+    func storeIntegerTokens(_ tokens: Set<Int>, for key: Key) {
+        integerTokensByKey.withLock { $0[key] = tokens }
+    }
+
+    func decimalTokens(for key: Key) -> Set<Int>? {
+        decimalTokensByKey.withLock { $0[key] }
+    }
+
+    func storeDecimalTokens(_ tokens: Set<Int>, for key: Key) {
+        decimalTokensByKey.withLock { $0[key] = tokens }
+    }
 }
 
 // MARK: - JSON Generator
@@ -194,6 +212,11 @@ struct ConstrainedJSONGenerator<Backend: TokenBackend> {
     }
 
     private static func buildValidIntegerTokens(backend: Backend) -> Set<Int> {
+        let cacheKey = stringTokenCacheKey(for: backend)
+        if let cached = StringTokenCache.shared.integerTokens(for: cacheKey) {
+            return cached
+        }
+
         var allowed = Set<Int>()
         for token in 0 ..< backend.vocabSize {
             if backend.isSpecialToken(token) { continue }
@@ -204,10 +227,17 @@ struct ConstrainedJSONGenerator<Backend: TokenBackend> {
                 allowed.insert(token)
             }
         }
+
+        StringTokenCache.shared.storeIntegerTokens(allowed, for: cacheKey)
         return allowed
     }
 
     private static func buildValidDecimalTokens(backend: Backend) -> Set<Int> {
+        let cacheKey = stringTokenCacheKey(for: backend)
+        if let cached = StringTokenCache.shared.decimalTokens(for: cacheKey) {
+            return cached
+        }
+
         var allowed = Set<Int>()
         for token in 0 ..< backend.vocabSize {
             if backend.isSpecialToken(token) { continue }
@@ -218,6 +248,8 @@ struct ConstrainedJSONGenerator<Backend: TokenBackend> {
                 allowed.insert(token)
             }
         }
+
+        StringTokenCache.shared.storeDecimalTokens(allowed, for: cacheKey)
         return allowed
     }