When backends are at capacity (per-model max_concurrent or the
process-wide --max-concurrent-backend-requests ceiling), the response
was 503. The OpenAI SDK, litellm, and most agent harnesses key on 429
for rate-limit backoff and treat 503 as a hard error.
Both saturation paths now return 429 with the existing Retry-After
header and type: "rate_limit_error" in the JSON body. The per-model
admission middleware keeps admission_rejected as the code field so
existing alerts that match on it still fire.
Non-saturation 503s are unchanged: model cold-loading (with progress
body), model-load failure cooldown, PII detector fail-closed, and
classifier unavailable. These mean "not ready" rather than "busy".
Assisted-by: AGENT:regolo/glm5.2 [TOOL]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Ettore Di Giacinto
7f3029e0d3