GPT-5-Codex Developer Guide: OpenAI's SWE-Optimized Model API Explained

GPT-5-Codex Developer Guide: OpenAI's SWE-Optimized Model API Explained

GPT-5-Codex is OpenAI’s software-engineering-optimized model family, built specifically for agentic coding tasks like feature development, debugging, and large-scale refactoring. Unlike general-purpose GPT models, it runs exclusively through the Responses API and powers the OpenAI Codex platform, which reached 4 million weekly active developers by April 2026. What Is GPT-5-Codex? Understanding OpenAI’s SWE-Optimized Model Family GPT-5-Codex is a specialized series of language models from OpenAI, purpose-built for software engineering tasks that require long-horizon reasoning, multi-file context comprehension, and autonomous code execution. Unlike general-purpose models such as GPT-5.5, the GPT-5-Codex family is optimized for agentic workflows — meaning it can plan a multi-step coding task, interact with tools like shells and file systems, and iterate on results without continuous human intervention. The original gpt-5-codex model was released on September 23, 2025, priced at $1.25 per 1M input tokens and $10.00 per 1M output tokens, and was immediately positioned as the backbone of OpenAI’s Codex platform. A critical distinction developers must understand: GPT-5-Codex is available only through the Responses API, not the older Chat Completions API — this is not a minor implementation detail, but a paradigm shift in how you structure API calls, tool use, and conversation state. The model family has since expanded through GPT-5.1-Codex, GPT-5.2-Codex, and GPT-5.3-Codex, each improving SWE-Bench Pro scores while introducing better context compaction and reduced output token overhead. ...

May 25, 2026 · 16 min · baeseokjae
GLM-5.1 Review 2026

GLM-5.1 Review 2026: #1 SWE-bench Pro, MIT License, $1/M Tokens

GLM-5.1 is the first open-weight model to claim the #1 position on SWE-Bench Pro, scoring 58.4 — ahead of GPT-5.4 (57.7) and Claude Opus 4.6 (57.3). Released April 7, 2026 by Z.AI under an MIT license, it costs $1.40/M input tokens versus Claude Opus 4.7’s $5.00/M, making it the most cost-effective frontier-class coding model available today. What Is GLM-5.1? The Open-Source Frontier Model from Z.AI GLM-5.1 is a 754B-parameter Mixture-of-Experts language model developed by Z.AI (formerly Zhipu AI) and released on April 7, 2026, under the MIT license. It activates only 40B parameters per forward pass via its sparse MoE routing, which delivers frontier-tier reasoning at significantly lower inference cost than dense models of comparable quality. The architecture combines DeepSeek Sparse Attention (DSA) for efficient long-context processing, a 203K-token context window, and asynchronous reinforcement learning via Z.AI’s proprietary “slime” training framework. In independent benchmarking by BenchLM, GLM-5.1 ranks 14th out of 115 models with an overall composite score of 83/100. What sets it apart is the combination of open weights, commercial-use permissive licensing, and a demonstrated capability peak at software engineering tasks that no prior open-weight model has matched. Teams can access it via the Z.AI API, self-host via Hugging Face and Ollama, or integrate it as a drop-in replacement for the OpenAI SDK through vLLM’s OpenAI-compatible endpoint. ...

May 15, 2026 · 12 min · baeseokjae
GLM-5.1 vs Claude vs GPT-6: Open-Source Model That Beats Frontier Models

GLM-5.1 vs Claude vs GPT-6: Open-Source Model That Beats Frontier Models

GLM-5.1 is the first open-weight model to top SWE-Bench Pro, scoring 58.4 against GPT-5.4 (57.7) and Claude Opus 4.6 (57.3) — at API prices 5–10x lower than Anthropic’s flagship. It is not a universal winner, but for coding and agentic tasks, it has genuinely closed the gap with frontier closed models. What Is GLM-5.1? The Open-Weight Model That Shocked the Leaderboard GLM-5.1 is an open-weight large language model released by Zhipu AI (Z.ai) in April 2026, built on a 754-billion-parameter Mixture-of-Experts (MoE) architecture that activates only 40 billion parameters per token — the same efficiency design used by Mixtral and DeepSeek-V3. On April 7, 2026, GLM-5.1 became the first open-source model to claim the global #1 position on Scale AI’s SWE-Bench Pro leaderboard, scoring 58.4% against GPT-5.4 at 57.7% and Claude Opus 4.6 at 57.3%. That ranking held for 9 days before Claude Opus 4.7 reclaimed the top spot at 64.3%. The model ships under an MIT license, runs on vLLM and SGLang, supports a 200K-token context window with up to 128K output tokens, and was trained entirely on Huawei Ascend 910B chips — zero Nvidia GPU involvement. As of May 2026, it sits at #18 overall on Chatbot Arena and holds the #1 open-source model slot. For teams doing high-volume code generation or autonomous agent workflows, GLM-5.1 is the first open-weight option worth taking seriously against paid frontier APIs. ...

May 15, 2026 · 14 min · baeseokjae
Qwen3-Coder Review 2026: The Open-Source Model That Rivals GPT-5

Qwen3-Coder Review 2026: The Open-Source Model That Rivals GPT-5

Qwen3-Coder is Alibaba’s open-source coding LLM family that scores 69–70% on SWE-bench Verified while costing 85x less than Claude Opus 4.6 — and the 80B Next variant runs on a single MacBook Pro with 48GB unified memory. If you’re running multi-model coding pipelines or need a cost-effective alternative for overnight refactors and batch PR triage, this is the model to benchmark first. What Is Qwen3-Coder and Why Does It Matter in 2026? Qwen3-Coder is a family of open-source Mixture-of-Experts (MoE) coding language models released by Alibaba’s Qwen team under the Apache 2.0 license. The lineup spans from a 1.5B model for IDE autocomplete all the way to a 480B MoE model for maximum benchmark performance. What makes the 2026 release significant is the convergence of two trends: open-source models have closed the SWE-bench gap to within single-digit percentage points of Claude Opus 4.6 (80.8%), while API pricing has dropped so dramatically that $0.22 per million input tokens is now viable for continuous coding workloads that would cost hundreds of dollars per day with GPT-5. The February 2026 wave saw six models released — MiniMax M2.5 (80.2%), GLM-5 (77.8%), Qwen3-Coder-Next (70.6%), among others — that would have each led all public benchmarks just 12 months earlier. For developers who self-host or use cost-sensitive pipelines, Qwen3-Coder is no longer a compromise. It is a first-choice option backed by serious infrastructure: RL training across 20,000 parallel environments on Alibaba Cloud using real GitHub issues, LeetCode challenges, and Codeforces problems. ...

April 24, 2026 · 11 min · baeseokjae