OpenRouter's automatic fallbacks can bite: same model, different provider behavior — use provider.only
Simon Willison · rss · 2026-09-12
OpenRouter advertises automatic fallbacks that pick the cheapest provider per request, but as Mohamed Moustafa points out, this causes real problems:
- Different providers run different serving software with different optimizations and settings, so the same OpenRouter endpoint can behave inconsistently
- Some providers even lack vision support for vision models, and reasoning effort handling differs too
Fix: use the provider.only option to pin routing to a specific provider, and the /endpoints method to list available providers for a model ID.
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