The LLM landscape in May 2026 looks nothing like it did a year ago. OpenAI just shipped GPT-5.5 Instant with 52.5% fewer hallucinations. Anthropic's Claude Mythos is matching it in cybersecurity benchmarks. Moonshot AI dropped Kimi K2.6 as an open-weight contender with agent swarm capabilities. xAI's Grok 4.3 came with steep price cuts. And Google's Gemma 4 is pushing multi-token prediction for faster inference. If you're building anything serious with LLMs, you're not picking one model — you're routing across five. And that's where things break. The Five Failure Modes Nobody Talks About After running multi-provider LLM routing in production for months, here are the patterns that bite hardest — and the ones that are completely invisible until your users start complaining. 1.…