diff --git a/.github/aw/compat.json b/.github/aw/compat.json
index 0ea0160b78a..0cc6b903db3 100644
--- a/.github/aw/compat.json
+++ b/.github/aw/compat.json
@@ -10,7 +10,7 @@
         "min-gh-aw": "0.72.0",
         "max-gh-aw": "*",
         "min-agent": "1.0.21",
-        "max-agent": "1.0.56",
+        "max-agent": "1.0.75",
         "open": true
       },
       {
diff --git a/Makefile b/Makefile
index e962bbd1c13..2b792d76db5 100644
--- a/Makefile
+++ b/Makefile
@@ -38,7 +38,7 @@ all: build
 
 # Build the binary, run make deps before this
 .PHONY: build
-build: sync-action-pins sync-action-scripts
+build: sync-action-pins sync-action-scripts sync-compat
 	go build $(LDFLAGS) -o $(BINARY_NAME) ./cmd/gh-aw
 
 # Build for all platforms
@@ -1105,6 +1105,16 @@ sync-action-scripts:
 	@cp install-gh-aw.ps1 actions/setup-cli/install.ps1
 	@echo "✓ Action scripts synced successfully"
 
+# Sync max-agent in the latest compat.json interval with DefaultCopilotVersion
+.PHONY: sync-compat
+sync-compat:
+	@bash scripts/sync-compat.sh
+
+# Check that compat.json is in sync with DefaultCopilotVersion (CI gate)
+.PHONY: check-stale-compat
+check-stale-compat:
+	@bash scripts/sync-compat.sh --check
+
 # Sync install-gh-aw.sh SHA/hash constants in pkg/cli/copilot_setup.go
 .PHONY: sync-install-script-hashes
 sync-install-script-hashes:
@@ -1301,6 +1311,8 @@ help:
 	@echo "  install          - Install binary locally"
 	@echo "  sync-action-pins - Sync actions-lock.json from .github/aw to pkg/actionpins/data and pkg/workflow/data (runs automatically during build)"
 	@echo "  sync-action-scripts - Sync install-gh-aw.sh and install-gh-aw.ps1 to actions/setup-cli/ (runs automatically during build)"
+	@echo "  sync-compat      - Sync max-agent in .github/aw/compat.json latest interval with DefaultCopilotVersion (runs automatically during build)"
+	@echo "  check-stale-compat - Guard: detect when compat.json max-agent is out of sync with DefaultCopilotVersion"
 	@echo "  sync-install-script-hashes - Update install-gh-aw.sh SHA and SHA256 constants in pkg/cli/copilot_setup.go (runs automatically during update)"
 	@echo "  update           - Update GitHub Actions and workflows, sync action pins, and rebuild binary"
 	@echo "  fix              - Apply automatic codemod-style fixes to workflow files (depends on build)"
diff --git a/scripts/sync-compat.sh b/scripts/sync-compat.sh
new file mode 100755
index 00000000000..0c2d4ba5004
--- /dev/null
+++ b/scripts/sync-compat.sh
@@ -0,0 +1,66 @@
+#!/bin/bash
+
+# sync-compat.sh - Keep .github/aw/compat.json in sync with DefaultCopilotVersion
+#
+# Reads DefaultCopilotVersion from pkg/constants/version_constants.go and updates
+# the max-agent field of the latest interval (the entry with "open": true) in
+# .github/aw/compat.json.
+#
+# Usage:
+#   sync-compat.sh [--check]
+#
+# Options:
+#   --check   Exit with code 1 if compat.json is out of sync instead of updating it.
+#
+# Exit codes:
+#   0 - compat.json is already in sync, or was updated successfully
+#   1 - compat.json is out of sync (only when --check is passed), or an error occurred
+
+set -euo pipefail
+
+# Script must be run from the repository root
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+CONSTANTS_FILE="$REPO_ROOT/pkg/constants/version_constants.go"
+COMPAT_FILE="$REPO_ROOT/.github/aw/compat.json"
+
+CHECK_ONLY=0
+for arg in "$@"; do
+  if [ "$arg" = "--check" ]; then
+    CHECK_ONLY=1
+  fi
+done
+
+# Extract DefaultCopilotVersion from Go constants file
+COPILOT_VERSION=$(grep -oP '^\s*const DefaultCopilotVersion\s+Version\s*=\s*"\K[^"]+' "$CONSTANTS_FILE")
+if [ -z "$COPILOT_VERSION" ]; then
+  echo "Error: could not extract DefaultCopilotVersion from $CONSTANTS_FILE" >&2
+  exit 1
+fi
+
+# Read the current max-agent of the latest interval (entry with "open": true)
+CURRENT_MAX_AGENT=$(jq -r '."agent-compat-v1".copilot[] | select(.open == true) | ."max-agent"' "$COMPAT_FILE")
+if [ -z "$CURRENT_MAX_AGENT" ] || [ "$CURRENT_MAX_AGENT" = "null" ]; then
+  echo "Error: could not find latest interval (\"open\": true) in $COMPAT_FILE" >&2
+  exit 1
+fi
+
+if [ "$CURRENT_MAX_AGENT" = "$COPILOT_VERSION" ]; then
+  echo "compat.json is already in sync (max-agent=$COPILOT_VERSION)"
+  exit 0
+fi
+
+if [ "$CHECK_ONLY" = "1" ]; then
+  echo "Error: compat.json is out of sync: max-agent=$CURRENT_MAX_AGENT, DefaultCopilotVersion=$COPILOT_VERSION" >&2
+  echo "Run 'make sync-compat' to update." >&2
+  exit 1
+fi
+
+# Update max-agent in the latest interval
+UPDATED=$(jq --arg version "$COPILOT_VERSION" \
+  '."agent-compat-v1".copilot = [."agent-compat-v1".copilot[] | if .open == true then ."max-agent" = $version else . end]' \
+  "$COMPAT_FILE")
+
+echo "$UPDATED" > "$COMPAT_FILE"
+echo "Updated compat.json: max-agent $CURRENT_MAX_AGENT -> $COPILOT_VERSION"