GPT-5.6 vs Fable 5: Benchmark Lead but Mixed Real-World Results

OpenAI recently fully released GPT-5.6 (Sol version), and Anthropic promptly reset user quotas, sparking a direct showdown between the two models. Official benchmarks show GPT-5.6 Sol leading in several metrics, but third-party evaluations and user tests reveal divergence: scores are close between GPT-5.6 and Fable 5, yet Fable 5 performs better in real-world tasks like complex project collaboration and 3D modeling.

Official Benchmarks: GPT-5.6 Leads in Multiple Areas

Data from OpenAI's launch event shows GPT-5.6 Sol leading Claude Mythos 5 by about 4 percentage points on Terminal-Bench 2.1, and surpassing Fable 5 by over ten points on Agents' Last Exam. On DeepSWE 1.1, Sol achieved the highest score with a single-task cost of about $8, less than half that of Fable 5. Vertically, on OpenAI's own AGI Index, 5.5 scored 43%, while 5.6 Sol jumped to 60%, a significant improvement.

Third-Party Evaluation: Intelligence Scores Close, Cost Advantage Clear

Initial data from Artificial Analysis shows Fable 5 leading the Intelligence Index v4.1 with 60 points, closely followed by GPT-5.6 Sol at 59 points, a mere 1-point gap. In terms of cost, Sol (max) spent $1.04 per Index task, far lower than Fable 5 (with fallback). On the Coding Agent leaderboard, Codex + Sol topped with 80 points, beating Claude Code + Fable 5's 77 points.

Real-World Experience: Fable 5 Excels in Complex Tasks

Multiple user feedback indicates that GPT-5.6 performs smoothly on general tasks (e.g., queries, loops), but falls short in deep project collaboration compared to Fable 5. One user assigned the same project to both models: Fable 5 completed it in about 10 minutes, while GPT-5.6 took over an hour, with rigid methods requiring frequent verification. Additionally, GPT-5.6's quota consumption is rapid: some users reported that completing just two moderate tasks consumed 80% of the 5-hour usage limit.

Specialized Test: 3D Modeling Gap Is Stark

In a 3D web application building test, GPT-5.6 Sol finished in just 7 minutes 40 seconds, but the result was described as "2.5D paper cutouts," with abnormal character and vehicle shapes. In contrast, Fable 5 took about 50 minutes, undergoing multiple rounds of autonomous verification and fixes, delivering a complete work featuring 10 vehicle types, 3D characters, multi-angle switching, paint switching, and more. Its 3D modeling and spatial awareness were significantly superior.

Other Release Information

• Codex has been renamed to ChatGPT Work, positioned as an agent workspace for non-programming users.
• The new ChatGPT desktop app integrates five entry points: Chat, Work, Codex, Scheduled, and Sites.
• GPT-5.4 will be deprecated on July 23, less than six months after its release.
• New Sites feature allows users to publish interactive websites directly in chat.
• GPT-5.5's "goblin" speech quirk has been largely suppressed in 5.6, with word frequency dropping from 0.405% to 0.032%.