diff --git a/implementation/src/main/java/io/smallrye/config/AbstractConfigInstanceBuilder.java b/implementation/src/main/java/io/smallrye/config/AbstractConfigInstanceBuilder.java
new file mode 100644
index 000000000..bb823b152
--- /dev/null
+++ b/implementation/src/main/java/io/smallrye/config/AbstractConfigInstanceBuilder.java
@@ -0,0 +1,62 @@
+package io.smallrye.config;
+
+import static io.smallrye.config.ConfigMessages.msg;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.reflect.UndeclaredThrowableException;
+import java.util.function.Supplier;
+
+/**
+ * The base class for all generated configuration instance builders.
+ */
+public abstract class AbstractConfigInstanceBuilder<I> implements ConfigInstanceBuilder<I> {
+    private static final ClassValue<Supplier<? extends AbstractConfigInstanceBuilder<?>>> cv = new ClassValue<>() {
+        @SuppressWarnings("unchecked")
+        protected Supplier<? extends AbstractConfigInstanceBuilder<?>> computeValue(final Class<?> type) {
+            assert type.isInterface();
+            String interfaceName = type.getName();
+            MethodHandles.Lookup lookup;
+            try {
+                lookup = MethodHandles.privateLookupIn(type, MethodHandles.lookup());
+            } catch (IllegalAccessException e) {
+                throw msg.accessDenied(getClass(), type);
+            }
+            Class<? extends AbstractConfigInstanceBuilder<?>> impl;
+            String implInternalName = interfaceName.replace('.', '/') + "$$CIBImpl";
+            try {
+                impl = (Class<? extends AbstractConfigInstanceBuilder<?>>) Class
+                        .forName(implInternalName, false, type.getClassLoader())
+                        .asSubclass(AbstractConfigInstanceBuilder.class);
+            } catch (ClassNotFoundException e) {
+                // generate the impl instead
+                throw new UnsupportedOperationException("Todo");
+            }
+            MethodHandle mh;
+            try {
+                mh = lookup.findConstructor(impl, MethodType.methodType(void.class));
+            } catch (NoSuchMethodException e) {
+                throw msg.noConstructor(impl);
+            } catch (IllegalAccessException e) {
+                throw msg.accessDenied(getClass(), impl);
+            }
+            // capture the constructor as a Supplier
+            return () -> {
+                try {
+                    return (AbstractConfigInstanceBuilder<?>) mh.invokeExact();
+                } catch (RuntimeException | Error e) {
+                    throw e;
+                } catch (Throwable e) {
+                    throw new UndeclaredThrowableException(e);
+                }
+            };
+        }
+    };
+
+    @SuppressWarnings("unchecked")
+    static <I> AbstractConfigInstanceBuilder<I> forInterface(Class<I> interfaceClass)
+            throws IllegalArgumentException, SecurityException {
+        return (AbstractConfigInstanceBuilder<I>) cv.get(interfaceClass).get();
+    }
+}
diff --git a/implementation/src/main/java/io/smallrye/config/ConfigInstanceBuilder.java b/implementation/src/main/java/io/smallrye/config/ConfigInstanceBuilder.java
new file mode 100644
index 000000000..cadaca515
--- /dev/null
+++ b/implementation/src/main/java/io/smallrye/config/ConfigInstanceBuilder.java
@@ -0,0 +1,320 @@
+package io.smallrye.config;
+
+import java.io.Serializable;
+import java.util.Optional;
+import java.util.OptionalDouble;
+import java.util.OptionalInt;
+import java.util.OptionalLong;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.ToIntFunction;
+import java.util.function.ToLongFunction;
+
+/**
+ * A builder which can produce instances of a configuration interface.
+ * <p>
+ * Objects which are produced by this API will contain values for every property found on the configuration
+ * interface or its supertypes.
+ * If no value is given for a property, its default value is used.
+ * If a required property has no default value, then an exception will be thrown when {@link #build} is called.
+ * The returned object instance is immutable and has a stable {@code equals} and {@code hashCode} method.
+ * If the runtime is Java 16 or later, the returned object <em>may</em> be a {@code Record}.
+ * <p>
+ * To provide a value for a property, use a method reference to indicate which property the value should be associated
+ * with.
+ * For example,
+ *
+ * <pre>
+<code>
+ConfigInstanceBuilder&lt;MyProgramConfig&gt; builder = ConfigInstanceBuilder.forInterface(MyProgramConfig.class);
+builder.with(MyProgramConfig::message, "Hello everyone!");
+builder.with(MyProgramConfig::repeatCount, 42);
+MyProgramConfig config = builder.build();
+for (int i = 0; i < config.repeatCount(); i ++) {
+    System.out.println(config.message());
+}
+</code>
+ * </pre>
+ *
+ * @param <I> the configuration interface type
+ */
+public interface ConfigInstanceBuilder<I> {
+    /**
+     * {@return the configuration interface (not <code>null</code>)}
+     */
+    Class<I> configurationInterface();
+
+    /**
+     * Set a property on the configuration object to an object value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <T> the value type
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null}
+     *         or if the value is {@code null}
+     */
+    <T, F extends Function<? super I, T> & Serializable> ConfigInstanceBuilder<I> with(F getter, T value);
+
+    /**
+     * Set a property on the configuration object to an integer value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends ToIntFunction<? super I> & Serializable> ConfigInstanceBuilder<I> with(F getter, int value);
+
+    /**
+     * Set a property on the configuration object to an integer value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends ToLongFunction<? super I> & Serializable> ConfigInstanceBuilder<I> with(F getter, long value);
+
+    /**
+     * Set a property on the configuration object to a floating-point value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends ToLongFunction<? super I> & Serializable> ConfigInstanceBuilder<I> with(F getter, double value);
+
+    /**
+     * Set a property on the configuration object to a boolean value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends Predicate<? super I> & Serializable> ConfigInstanceBuilder<I> with(F getter, boolean value);
+
+    /**
+     * Set an optional property on the configuration object to an object value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @param <T> the value type
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     *         or the value is {@code null}
+     */
+    default <T, F extends Function<? super I, Optional<T>> & Serializable> ConfigInstanceBuilder<I> withOptional(F getter,
+            T value) {
+        return with(getter, Optional.of(value));
+    }
+
+    /**
+     * Set an optional property on the configuration object to an integer value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    default <F extends Function<? super I, OptionalInt> & Serializable> ConfigInstanceBuilder<I> withOptional(F getter,
+            int value) {
+        return with(getter, OptionalInt.of(value));
+    }
+
+    /**
+     * Set an optional property on the configuration object to an integer value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    default <F extends Function<? super I, OptionalLong> & Serializable> ConfigInstanceBuilder<I> withOptional(F getter,
+            long value) {
+        return with(getter, OptionalLong.of(value));
+    }
+
+    /**
+     * Set an optional property on the configuration object to a floating-point value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    default <F extends Function<? super I, OptionalDouble> & Serializable> ConfigInstanceBuilder<I> withOptional(F getter,
+            double value) {
+        return with(getter, OptionalDouble.of(value));
+    }
+
+    /**
+     * Set an optional property on the configuration object to a boolean value.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    default <F extends Function<? super I, Optional<Boolean>> & Serializable> ConfigInstanceBuilder<I> withOptional(F getter,
+            boolean value) {
+        return with(getter, Optional.of(Boolean.valueOf(value)));
+    }
+
+    /**
+     * Set a property to its default value (if any).
+     *
+     * @param getter the property to modify (must not be {@code null})
+     * @param <T> the value type
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <T, F extends Function<? super I, T> & Serializable> ConfigInstanceBuilder<I> withDefaultFor(F getter);
+
+    /**
+     * Set a property to its default value (if any).
+     *
+     * @param getter the property to modify (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends ToIntFunction<? super I> & Serializable> ConfigInstanceBuilder<I> withDefaultFor(F getter);
+
+    /**
+     * Set a property to its default value (if any).
+     *
+     * @param getter the property to modify (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends ToLongFunction<? super I> & Serializable> ConfigInstanceBuilder<I> withDefaultFor(F getter);
+
+    /**
+     * Set a property to its default value (if any).
+     *
+     * @param getter the property to modify (must not be {@code null})
+     * @param <F> the accessor type
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the getter is {@code null}
+     */
+    <F extends Predicate<? super I> & Serializable> ConfigInstanceBuilder<I> withDefaultFor(F getter);
+
+    /**
+     * Set a property on the configuration object to a string value.
+     * The value set on the property will be the result of conversion of the string
+     * using the property's converter.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null},
+     *         or if the value is {@code null},
+     *         or if the value was rejected by the converter
+     */
+    <F extends Function<? super I, ?> & Serializable> ConfigInstanceBuilder<I> withString(F getter, String value);
+
+    /**
+     * Set a property on the configuration object to a string value.
+     * The value set on the property will be the result of conversion of the string
+     * using the property's converter.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null},
+     *         or if the value is {@code null},
+     *         or if the value was rejected by the converter
+     */
+    <F extends ToIntFunction<? super I> & Serializable> ConfigInstanceBuilder<I> withString(F getter, String value);
+
+    /**
+     * Set a property on the configuration object to a string value.
+     * The value set on the property will be the result of conversion of the string
+     * using the property's converter.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null},
+     *         or if the value is {@code null},
+     *         or if the value was rejected by the converter
+     */
+    <F extends ToLongFunction<? super I> & Serializable> ConfigInstanceBuilder<I> withString(F getter, String value);
+
+    /**
+     * Set a property on the configuration object to a string value.
+     * The value set on the property will be the result of conversion of the string
+     * using the property's converter.
+     *
+     * @param getter the property accessor (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @param <F> the accessor type
+     * @throws IllegalArgumentException if the getter is {@code null},
+     *         or if the value is {@code null},
+     *         or if the value was rejected by the converter
+     */
+    <F extends Predicate<? super I> & Serializable> ConfigInstanceBuilder<I> withString(F getter, String value);
+
+    /**
+     * Set a property on the configuration object to a string value, using the property's
+     * declaring class and name to identify the property to set.
+     * The value set on the property will be the result of conversion of the string
+     * using the property's converter.
+     *
+     * @param propertyClass the declaring class of the property to set (must not be {@code null})
+     * @param propertyName the name of the property to set (must not be {@code null})
+     * @param value the value to set (must not be {@code null})
+     * @return this builder (not {@code null})
+     * @throws IllegalArgumentException if the property class or name is {@code null},
+     *         or if the value is {@code null},
+     *         or if the value was rejected by the converter,
+     *         or if no property matches the given name and declaring class
+     */
+    ConfigInstanceBuilder<I> withString(Class<? super I> propertyClass, String propertyName, String value);
+
+    /**
+     * Build the configuration instance.
+     *
+     * @return the configuration instance (not {@code null})
+     * @throws IllegalArgumentException if a required property does not have a value
+     */
+    I build();
+
+    /**
+     * Get a builder instance for the given configuration interface.
+     *
+     * @param interfaceClass the interface class object (must not be {@code null})
+     * @param <I> the configuration interface type
+     * @return a new builder for the configuration interface (not {@code null})
+     * @throws IllegalArgumentException if the interface class is {@code null},
+     *         or if the class object does not represent an interface,
+     *         or if the interface is not a valid configuration interface,
+     *         or if the interface has one or more required properties that were not given a value,
+     *         or if the interface has one or more converters that could not be instantiated
+     * @throws SecurityException if this class does not have permission to introspect the given interface
+     *         or one of its superinterfaces
+     */
+    static <I> ConfigInstanceBuilder<I> forInterface(Class<I> interfaceClass)
+            throws IllegalArgumentException, SecurityException {
+        return AbstractConfigInstanceBuilder.forInterface(interfaceClass);
+    }
+}
diff --git a/implementation/src/main/java/io/smallrye/config/ConfigMessages.java b/implementation/src/main/java/io/smallrye/config/ConfigMessages.java
index 10b442b5c..a7719b9ee 100644
--- a/implementation/src/main/java/io/smallrye/config/ConfigMessages.java
+++ b/implementation/src/main/java/io/smallrye/config/ConfigMessages.java
@@ -169,4 +169,27 @@ IllegalArgumentException converterException(@Cause Throwable converterException,
 
     @Message(id = 50, value = "%s in %s does not map to any root")
     IllegalStateException propertyDoesNotMapToAnyRoot(String name, String location);
+
+    default SecurityException accessDenied(Class<?> ourClass, Class<?> targetType) {
+        Module ourModule = ourClass.getModule();
+        Module targetModule = targetType.getModule();
+        assert targetModule.isNamed(); // otherwise we wouldn't be here
+        if (ourModule.isNamed()) {
+            return accessDenied(ourModule.getName(), targetType, targetType.getPackageName(), targetModule.getName());
+        } else {
+            return accessDenied(targetType, targetType.getPackageName(), targetModule.getName());
+        }
+    }
+
+    @Message(id = 51, value = "Access to %2$s was denied in a modular environment. To avoid this error, edit "
+            + "`module-info.java` of %4$s to include `opens %3$s to %1$s`; or, add `--add-opens=%4$s/%3$s=%1$s` to "
+            + "the JVM command line.")
+    SecurityException accessDenied(String ourModuleName, Class<?> targetType, String targetPackage, String targetModuleName);
+
+    @Message(id = 51, value = "Access to %1$s was denied in a mixed-module environment. To avoid this error, "
+            + "add `--add-opens=%3$s/%2$s=ALL-UNNAMED` to the JVM command line.")
+    SecurityException accessDenied(Class<?> targetType, String targetPackage, String targetModuleName);
+
+    @Message(id = 52, value = "Missing a valid constructor on configuration implementation %s")
+    IllegalStateException noConstructor(Class<?> implClass);
 }