Benchmark results attributed to internal OpenAI testers began circulating this week, consistent with a June 2026 release window for GPT-5.6. The leaked data points to two headline improvements: enhanced reasoning accuracy for multi-step agentic workflows, and significantly improved performance on tasks requiring sustained logical consistency across long chains of reasoning.
What the Leaked Benchmarks Show
Based on data circulating in AI research communities, GPT-5.6 reportedly achieves:
- Terminal-Bench 2.1: ~79% — up from GPT-5.5’s 74% on autonomous agent tasks
- Multi-step agentic reasoning: significant improvement on tasks requiring 10+ sequential decisions
- Hallucination rate: further reduction below GPT-5.5’s already-industry-leading benchmark
- Code generation consistency: improved performance on complex multi-file codebases
What GPT-5.6 Is Designed to Fix
GPT-5.5 made headlines for cutting hallucinations by 52% versus GPT-5. GPT-5.6 appears focused on a different limitation — the tendency of even strong models to drift or make compounding errors in long agentic workflows where each step depends on the accuracy of previous steps.
- Long-horizon task completion — maintaining accuracy across 20, 30 or 50-step automated workflows
- Tool-use reliability — better decisions about when to call external tools vs. answer from knowledge
- Plan adherence — staying on the original task plan even when individual steps surface unexpected information
Expected Pricing and Availability
No official pricing has been confirmed. Based on OpenAI’s recent cadence, GPT-5.6 is expected to replace GPT-5.5 in the API with similar or slightly reduced pricing, and appear in ChatGPT Plus and Team plans at launch. A free-tier rollout would likely follow 4–6 weeks after the paid launch.