So you want to use OpenRouter?
Simon Willison’s Weblog
Subscribe
11th September 2026 - Link Blog
So you want to use OpenRouter? (via) One of OpenRouter's selling points is that it "handles fallbacks automatically and picks the most cost-effective option for each request", so you can call a single API endpoint for a model and get routed to the best available backend provider.
Mohamed Moustafa points out a whole set of ways that this can cause you problems. Different providers run different serving software with different optimizations and settings, which means that the same OpenRouter endpoint can serve model requests that behave in different ways.
Some providers even lack vision capability for vision models, and the way the reasoning effort option is processed can differ as well.
Thankfully you can control which provider is routed to using the provider.only option. The /endpoints method returns the list of available providers for a specific model ID.
Recent articles
Some thoughts on the Navier–Stokes Millennium Prize Problem - 8th September 2026
The Pelican comparison grid for Astra is pretty interesting - 4th September 2026
OpenAI's rogue agents were caught communicating via public wikis - 4th September 2026
This is a link post by Simon Willison, posted on 11th September 2026.
ai 2,230
generative-ai 1,976
llms 1,942
openrouter 32
Monthly briefing
Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments.
Pay me to send you less!
Sponsor & subscribe
Disclosures
Colophon
©
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026