Stop Giving Your Agent Tools. Give It a Sandbox - Mikyo King, Arize AI

Classic tool-calling agents fill their context with tool catalogs and raw outputs. Code mode gives the agent a sandbox and lets it search for and compose tools in code, returning only what it needs. Mikyo King, head of open source at Arize AI, explains why code mode works, how Arize built it into Phoenix (Bash, a Python sandbox, SQL and even UI control), its hidden costs (secrets, permissions, durability, double sandboxing), and how Harbor evals showed 43% fewer tokens and 31% lower cost. Chapters: 0:00 Intro 0:36 The line between engineers and everyone else is dissolving 1:52 The classic tool-calling agent 3:03 What is code mode? 4:37 Why code mode works 6:11 How Phoenix uses code mode 8:19 The hidden costs of code mode 10:42 Open problems 11:44 Evaluating code mode with Harbor 12:55 Results: 43% fewer tokens, 31% lower cost 13:59 Takeaways Mikyo King https://arize.com Join us in SF for the second annual AIE CODE summit: https://aie.codes our last flagship summit of 2026. Applications live now!