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Launch3w ago

OpenAI Launches GPT-5.6 Models with Enhanced Capabilities

Simon Willison1 min brief

In brief

  • OpenAI has released its new GPT-5.6 models-Luna, Terra, and Sol-available for widespread use starting today.
    • These models are priced per 1 million input/output tokens, ranging from $1/$6 for Luna to $5/$30 for Sol.
  • While the pricing is competitive with other leading models like Claude Opus, the real innovation lies in their capabilities.
  • The GPT-5.6 series boasts a February 2026 knowledge cutoff and an impressive million-token context window.
  • Its standout feature is its improved "long-running agentic performance," as demonstrated by beating Claude Fable 5 in tasks across 55 professional fields, including coding.
  • However, while GPT-5.6 Sol excelled in these benchmarks, it underperformed compared to Fable 5 on the SWE-Bench Pro evaluation, where it scored 64.6% versus Fable 5's 80%.
  • OpenAI has since flagged issues with SWE-Bench Pro, suggesting that nearly 30% of its tasks may be flawed.
  • The models introduce new API features like Programmatic Tool Calling, which enables them to execute JavaScript and orchestrate tool calls, bridging the gap between model-based and terminal-based utility use.
    • This could enhance their versatility for developers.
  • As OpenAI continues to refine these tools, users can expect further improvements in efficiency and cost-effectiveness.

Terms in this brief

Luna
One of OpenAI's new GPT-5.6 models, designed for specific use cases with lower cost and fewer capabilities compared to more advanced models like Sol.
Sol
The most powerful model in OpenAI's GPT-5.6 series, known for its high performance across various professional tasks but also noted for higher costs.
SWE-Bench Pro
A benchmark test evaluating AI's ability to fix real bugs from open-source software projects on GitHub, considered a practical measure of coding skills.

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