AI21 Labs Publishes Debugging Tale of vLLM Bug Affecting Jamba Model

Jul 11, 2026

AI21 Labs discovered a rare bug in vLLM that caused their new Jamba model to generate gibberish about once every thousand prompts. The issue was traced to how vLLM's scheduler interacts with different model architectures. AI21 Labs shared their fix and insights from the debugging process.

Why it matters: This highlights the subtle bugs that can arise in inference engines when supporting diverse model architectures, and the importance of thorough testing.

Full story at: AI21 Labs ↗