OpenAI's Codex development environment is undergoing significant changes, with a recent tweet highlighting a new "Fast mode" now becoming default for some users. Jinjing Liang, via a social media post, noted, > "Ok this explains my crazy usage... According to @OpenAI's Codex release notes, Fast mode is indeed now the default." This observation comes amidst OpenAI's broader rollout of its latest models.
The newly introduced "Fast mode" for Codex, specifically with the GPT-5.5 model, promises a 1.5 times speed improvement for users. However, this enhanced performance comes with a notable increase in cost, priced at 2.5 times more than standard usage, as reported by TheNewStack. This suggests that while speed is boosted, users should anticipate higher expenses for utilizing this accelerated capability.
This Fast mode is part of the larger launch of OpenAI's GPT-5.5 and GPT-5.5 Pro models, described as the company's most capable and efficient frontier models to date. These updates are rolling out across ChatGPT, the API, and Codex, focusing on advanced reasoning, coding, and agentic workflows. OpenAI aims for GPT-5.5 to be a "true agent" capable of handling multi-step, long-horizon tasks autonomously.
Earlier updates to Codex also included a "/fast" mode for GPT-5.4, offering similar speed improvements, according to a LinkedIn post by Hans Kärtner. The introduction of GPT-5.4 mini in Codex was also noted for providing a fast and efficient option for lighter coding tasks. These continuous enhancements underscore OpenAI's commitment to improving the speed and efficiency of its coding assistant.
The shift towards faster, more powerful models and modes in Codex reflects an evolving landscape where performance often correlates with increased resource utilization and cost. While the tweet suggests a default activation, the broader context from OpenAI's announcements indicates that "Fast mode" for GPT-5.5 is an available option, potentially becoming a default for specific premium plans or high-demand scenarios, impacting user experience and expenditure.
