diff --git a/.github/workflows/spec-sync-on-merge.yml b/.github/workflows/spec-sync-on-merge.yml
index fd62c4034f..d7ac487c8e 100644
--- a/.github/workflows/spec-sync-on-merge.yml
+++ b/.github/workflows/spec-sync-on-merge.yml
@@ -147,11 +147,10 @@ jobs:
           # Get the tree SHA from the base commit (base_tree requires a tree SHA, not a commit SHA)
           BASE_TREE_SHA=$(gh api "repos/${SPEC_REPO}/git/commits/${BASE_SHA}" --jq '.tree.sha')
 
-          # Create blob and commit via API (commits created through the API are automatically signed by GitHub)
-          BLOB_SHA=$(gh api "repos/${SPEC_REPO}/git/blobs" \
-            -f "content=$(base64 -w 0 controller.json)" \
-            -f "encoding=base64" \
-            --jq '.sha')
+          # Create blob via API using --input to avoid ARG_MAX limit on large specs
+          BLOB_SHA=$(base64 -w 0 controller.json | \
+            jq -Rs '{content: ., encoding: "base64"}' | \
+            gh api "repos/${SPEC_REPO}/git/blobs" --input - --jq '.sha')
 
           TREE_SHA=$(gh api "repos/${SPEC_REPO}/git/trees" \
             -f "base_tree=${BASE_TREE_SHA}" \