diff --git a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/AbstractArrayHttpHeaders.java b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/AbstractArrayHttpHeaders.java
index 8ddbcd455d..0474c1e745 100644
--- a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/AbstractArrayHttpHeaders.java
+++ b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/AbstractArrayHttpHeaders.java
@@ -232,6 +232,13 @@ public void forEachEntry(BiConsumer<String, String> consumer) {
         }
     }
 
+    @Override
+    public <C> void forEachEntry(C contextValue, HeaderWithValueConsumer<C> consumer) {
+        for (int i = 0; i < size * 2; i += 2) {
+            consumer.accept(contextValue, array[i], array[i + 1]);
+        }
+    }
+
     /**
      * Create a new ArrayHttpHeaders by copying raw array data.
      */
diff --git a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ArrayHttpHeaders.java b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ArrayHttpHeaders.java
index 0a67b275df..3960233618 100644
--- a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ArrayHttpHeaders.java
+++ b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ArrayHttpHeaders.java
@@ -34,7 +34,8 @@ final class ArrayHttpHeaders extends AbstractArrayHttpHeaders implements Modifia
      * @param key   pre-interned header name (must be from HeaderNameRegistry)
      * @param value header value
      */
-    void addHeaderCanonical(String key, String value) {
+    @Override
+    public void addHeaderCanonical(String key, String value) {
         ensureCapacity();
         int idx = size * 2;
         array[idx] = key;
@@ -44,9 +45,14 @@ void addHeaderCanonical(String key, String value) {
 
     @Override
     public void addHeaderTrusted(HeaderName name, String value) {
+        addHeaderTrusted(name.name(), value);
+    }
+
+    @Override
+    public void addHeaderTrusted(String name, String value) {
         ensureCapacity();
         int idx = size * 2;
-        array[idx] = name.name();
+        array[idx] = name;
         array[idx + 1] = value;
         size++;
     }
diff --git a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/HeaderName.java b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/HeaderName.java
index 561996e88a..feed036f44 100644
--- a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/HeaderName.java
+++ b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/HeaderName.java
@@ -90,6 +90,11 @@ public final class HeaderName {
     public static final HeaderName AMZ_SDK_REQUEST = HeaderName.builtin("amz-sdk-request");
     public static final HeaderName X_AMZN_REQUESTID = HeaderName.builtin("x-amzn-requestid");
     public static final HeaderName X_AMZN_TRACE_ID = HeaderName.builtin("x-amzn-trace-id");
+    public static final HeaderName X_AMZ_CHECKSUM_CRC32 = HeaderName.builtin("x-amz-checksum-crc32");
+    public static final HeaderName X_AMZ_CHECKSUM_CRC32C = HeaderName.builtin("x-amz-checksum-crc32c");
+    public static final HeaderName X_AMZ_CHECKSUM_CRC64NVME = HeaderName.builtin("x-amz-checksum-crc64nvme");
+    public static final HeaderName X_AMZ_CHECKSUM_SHA1 = HeaderName.builtin("x-amz-checksum-sha1");
+    public static final HeaderName X_AMZ_CHECKSUM_SHA256 = HeaderName.builtin("x-amz-checksum-sha256");
     public static final HeaderName X_AMZ_CONTENT_SHA256 = HeaderName.builtin("x-amz-content-sha256");
     public static final HeaderName X_AMZ_DATE = HeaderName.builtin("x-amz-date");
     public static final HeaderName X_AMZ_REQUEST_ID = HeaderName.builtin("x-amz-request-id");
diff --git a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ModifiableHttpHeaders.java b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ModifiableHttpHeaders.java
index ef41d730a1..48166b8cc7 100644
--- a/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ModifiableHttpHeaders.java
+++ b/http/http-api/src/main/java/software/amazon/smithy/java/http/api/ModifiableHttpHeaders.java
@@ -68,6 +68,16 @@ default void addHeader(HeaderName name, List<String> values) {
         addHeader(name.name(), values);
     }
 
+    /**
+     * Add a header with a pre-canonicalized name.
+     *
+     * <p>Use this when {@code name} is already canonical lowercase. The value is
+     * still normalized and validated.
+     */
+    default void addHeaderCanonical(String name, String value) {
+        addHeader(name, value);
+    }
+
     /**
      * Adds the given {@code headers}, similarly to if {@link #addHeader(String, List)} were to be called for each
      * entry in the given map.
@@ -181,6 +191,17 @@ default void addHeaderTrusted(HeaderName name, String value) {
         addHeader(name, value);
     }
 
+    /**
+     * Add a header with a pre-canonicalized name and pre-validated value, bypassing
+     * name canonicalization and value normalization when supported.
+     *
+     * <p>Use this only when {@code name} is already canonical lowercase and
+     * {@code value} is known to be valid.
+     */
+    default void addHeaderTrusted(String name, String value) {
+        addHeader(name, value);
+    }
+
     /**
      * Remove a header and its values by name.
      *