How to Add LLM Failover to Your Application

Build resilient AI features that stay online even when individual LLM providers experience outages or degraded performance.

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Identify common failure modes

LLM APIs fail in several ways: full outages, elevated error rates, latency spikes, rate-limit throttling, and degraded output quality. Map each failure mode to its impact on your users so you can prioritize which ones to handle first. Provider status pages and your own error logs are the best sources of historical data.

Define your fallback chain

For each primary model, designate one or two fallback models from different providers. For example, if GPT-5.2 is your primary, fall back to Claude Sonnet 4.5, then Gemini 3 Flash. Cross-provider fallbacks protect you from single-provider outages. LLMWise Mesh mode lets you define these chains in a single API call.

Configure circuit breakers

A circuit breaker tracks consecutive failures and temporarily removes a failing model from rotation. After a cooldown period, it sends a test request to check recovery. LLMWise uses a three-strike circuit breaker with a 30-second open window and automatic half-open retry, so you get failover without writing the logic yourself.

Add health checks and monitoring

Ping each provider periodically with lightweight requests to detect degradation before user traffic is affected. Log every failover event with the reason, fallback model used, and added latency. These logs feed your optimization loop and help you negotiate SLAs with providers.

Test under realistic load

Simulate provider failures in staging by injecting errors and latency. Verify that failover triggers correctly, that response quality from fallback models is acceptable, and that your circuit breakers recover when the primary comes back. LLMWise Replay Lab lets you re-run historical requests through alternate model chains to validate failover behavior before deploying changes.

Key takeaways

✓Cross-provider fallback chains are the simplest way to eliminate single points of failure in your AI stack.

✓LLMWise Mesh mode implements circuit-breaker failover across nine models with zero custom infrastructure.

✓Always test failover in staging with injected failures before relying on it in production.

Common questions

How fast does failover add to response latency?

A well-implemented circuit breaker adds near-zero latency during normal operation. When failover triggers, the added time is the latency of the fallback model's first token. LLMWise Mesh mode typically fails over in under 200 milliseconds because the circuit breaker short-circuits without waiting for a timeout.

Can I fail over between models from the same provider?

You can, but it offers limited protection against full provider outages. For maximum resilience, pair models from different providers. For example, use GPT-5.2 as primary with Claude Sonnet 4.5 as the first fallback, so an OpenAI outage does not take your feature offline.

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