Tokenless

Responses API

Codex, Behind the Harness — Dominik Kundel, OpenAI

Codex, Behind the Harness — Dominik Kundel, OpenAI

Once GPT 5.3 Codex Spark achieved 1000 tokens/sec on Cerebras, network latency superseded inference as the bottleneck for agents. This talk details how the Codex harness addresses this and other agentic challenges through innovations like WebSocket mode for stateful context, deferred tools for efficient context construction, robust sandboxing (Seatbelt, Bubblewrap, custom Windows solution), and an auto-review subagent to mitigate approval fatigue while ensuring security. It also covers structured actions via 'apply patch' for file edits, shell tools for system interaction, and sophisticated long-horizon goal management, with most distinct features exposed through the open Responses API.

Build Hour: Responses API

Build Hour: Responses API

A deep dive into the OpenAI Responses API, covering its architecture, advantages over Chat Completions, and practical applications for building persistent, multimodal agents with GPT-5, including live demos on migration and multi-tool workflows.

Build Hour: GPT-5

Build Hour: GPT-5

OpenAI's Build Hour provides a deep dive into GPT-5, showcasing its advanced coding and agentic capabilities. The session covers the new Responses API, critical for leveraging the model's reasoning, along with new parameters for steerability and practical prompting techniques for building complex, reliable applications.

Build Hour: Built-In Tools

Build Hour: Built-In Tools

Built-in tools like web search, file search, and code interpreter allow developers to extend model capabilities out-of-the-box. This summary covers the concepts, compares them to function calling, and details a demo of building a data exploration dashboard using multiple tools in concert.

Build Hour: Agentic Tool Calling

Build Hour: Agentic Tool Calling

A deep dive into building agentic systems using OpenAI's latest APIs. The session covers the core concept of 'agentic tool calling' (reasoning + tools), outlines a four-part framework (Agent, Infrastructure, Product, Evaluation) for designing long-horizon tasks, and provides a hands-on demonstration of building a non-blocking task processing system with a real-time progress UI.