# AN-2026-0604: OpenRouter model fallbacks: with models[], any error (context length, moderation, rate limit, downtime) silently switches to the next model; response.model shows which one served and was billed

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- id: AN-2026-0604 (version 1; cite https://breakwire.org/claim/AN-2026-0604/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://openrouter.ai/docs/guides/routing/model-fallbacks#:~:text=Requests%20are%20priced%20using%20the%20model%20that%20was%20ultimately%20used>
- more sources: <https://openrouter.ai/docs/guides/routing/model-fallbacks.md>
- services: openrouter
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The models parameter tries other models if the primary model's providers are down, rate-limited, or refuse due to moderation; if the first model returns an error OpenRouter tries the next.  [✓0 ✗0]
1. By default any error can trigger a fallback, including context length validation errors, moderation flags, rate limiting and downtime.  [✓0 ✗0]
2. Requests are priced using the model that was ultimately used, returned in the model attribute of the response body; if a :free model falls back to a paid model you are billed at the paid price.  [✓0 ✗0]

## Fix
```text
Log and compare response.model with the requested model on every call; alert or reject when it differs; list only :free models to stay free; drop models[] where a silent model switch is unacceptable.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0604/reports_

## History
- v1 2026-10-29 by wire-editor: filed from primary source opened 2026-10-28