Fallback Chains (Stable)

Define an ordered list of models/providers. On error or policy match, advance to the next. Pseudocode:

// let chain = FallbackChain::new()
//     .primary("gpt-4o")
//     .on_timeout("claude-3-haiku")
//     .always("mistral-medium");
// let client = AiClientBuilder::new(Provider::OpenAI).fallback(chain).build()?;

First success short-circuits the chain. Combine with racing for tail latency reduction.

Basic Failover (OSS)

AiClient::with_failover(Vec<Provider>) provides lightweight provider-level failover: when retryable errors occur (network, timeout, rate limit, 5xx), it attempts fallback providers in sequence. When used with routing_mvp, the selected model is preserved during failover.

use ai_lib::{AiClient, Provider};

let client = AiClient::new(Provider::OpenAI)?
    .with_failover(vec![Provider::Anthropic, Provider::Groq]);

Note: Advanced weighted/cost and SLO-aware strategies are available in ai-lib-pro.