diff --git a/agent/run.sh b/agent/run.sh
index 810794ad..bd7747c9 100755
--- a/agent/run.sh
+++ b/agent/run.sh
@@ -30,7 +30,7 @@ Environment variables (required):
   AWS_REGION        AWS region for Bedrock (e.g., us-east-1)
 
 Environment variables (optional):
-  ANTHROPIC_MODEL   Model to use (default: us.anthropic.claude-sonnet-4-6)
+  ANTHROPIC_MODEL   Model to use (unset: defer to the agent runtime default)
   DRY_RUN           Set to 1 to validate config and print prompt without running the agent
   MAX_TURNS         Max agent turns (default: 100)
 
@@ -205,13 +205,15 @@ DOCKER_ARGS=(
     -e "CLAUDE_CODE_USE_BEDROCK=1"
     -e "AWS_REGION=${AWS_REGION}"
     -e "GITHUB_TOKEN=${GITHUB_TOKEN}"
-    -e "ANTHROPIC_MODEL=${ANTHROPIC_MODEL:-us.anthropic.claude-sonnet-4-6}"
 )
 
 # Repo URL (may be empty in server mode — sent via payload)
 [[ -n "${REPO_URL}" ]] && DOCKER_ARGS+=(-e "REPO_URL=${REPO_URL}")
 
-# Optional env vars
+# Optional env vars. Pass each through only when the caller actually set it, so an
+# unset variable leaves the agent runtime's own default (agent/src/config.py) intact
+# instead of being shadowed by a second default defined here.
+[[ -n "${ANTHROPIC_MODEL:-}" ]] && DOCKER_ARGS+=(-e "ANTHROPIC_MODEL=${ANTHROPIC_MODEL}")
 [[ -n "${ISSUE_NUMBER}" ]] && DOCKER_ARGS+=(-e "ISSUE_NUMBER=${ISSUE_NUMBER}")
 [[ -n "${TASK_DESCRIPTION}" ]] && DOCKER_ARGS+=(-e "TASK_DESCRIPTION=${TASK_DESCRIPTION}")
 [[ -n "${DRY_RUN:-}" ]] && DOCKER_ARGS+=(-e "DRY_RUN=${DRY_RUN}")