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LMArena Bridge proxies every chat request through one of four transports. Selection is fully automatic — the bridge tracks challenge outcomes and switches transports when the current one starts failing.

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The four transports

TransportFunctionTypical use case
Direct httpxStandard async HTTP via httpx.AsyncClientMost models under normal conditions
Chrome fetch (fetch_lmarena_stream_via_chrome)Headless Chrome/Edge via Playwright; executes fetch() in-pageModels that always require a real browser; reCAPTCHA v3 token minting
Camoufox fetch (fetch_lmarena_stream_via_camoufox)Firefox-based stealth browser; uses main_world_eval=TrueFallback when Chrome is blocked or failing
Userscript proxy (fetch_lmarena_stream_via_userscript_proxy)Long-poll queue served to a browser userscript or internal Camoufox workerNo auth token configured

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Selection logic

The bridge follows these rules in order when selecting a transport for each request:
1

Check for strict-browser models

If the requested model is in STRICT_BROWSER_FETCH_MODELS (gemini-3-pro-grounding, gemini-exp-1206), the bridge always uses Chrome fetch regardless of any other state.
2

Check for auth token

If no auth token is present in config.json, the bridge prefers the userscript proxy transport. This allows anonymous use through a real browser tab.
3

Apply Chrome/Camoufox failure counters

For all other requests, the bridge tracks consecutive reCAPTCHA validation failures per browser transport:
  • After 2 or more consecutive Chrome reCAPTCHA failures → switches to Camoufox
  • After 2 or more consecutive Camoufox failures → switches back to Chrome
4

Fall back to direct httpx

When no browser transport is needed and an auth token is available, the bridge uses direct httpx.
Transport selection is automatic. You do not normally configure it. The only relevant config.json fields are the window mode keys (chrome_fetch_window_mode, camoufox_fetch_window_mode, camoufox_proxy_window_mode), which control whether browser windows are hidden or visible.

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Periodic refresh

The bridge runs periodic_refresh_task() on startup and then every 30 minutes in the background.
ConstantValue
PERIODIC_REFRESH_INTERVAL_SECONDS1800 (30 minutes)
During each refresh cycle, the bridge re-scrapes the LMArena page to discover updated reCAPTCHA sitekeys and actions, re-fetches the models list, and optionally mints a fresh reCAPTCHA v3 token. This keeps the bridge functional after LMArena deploys configuration changes.
If you notice persistent recaptcha validation failed errors, trigger a manual refresh from the /dashboard admin UI rather than restarting the server.

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