Quick Take

Released in June 2026, these two models represent the latest offerings from OpenAI and Anthropic. GPT-5.5 Instant (released June 25, 2026) positions itself as an efficient, cost-effective solution. Conversely, Claude Fable 5 (released June 9, 2026) focuses on high-effort, adaptive reasoning, boasting significantly higher intelligence and coding indices.

Benchmark Read

Claude Fable 5 consistently outperforms GPT-5.5 Instant across all shared metrics. In the Intelligence index, Claude Fable 5 scores 59.9 compared to 28.9 for GPT-5.5 Instant. The disparity continues in the Coding index, where Claude Fable 5 reaches 76.5 against GPT-5.5 Instant’s 39.4.

Specific benchmark performance is as follows:

• GPQA: Claude Fable 5 (0.926) vs. GPT-5.5 Instant (0.823)
• HLE: Claude Fable 5 (0.533) vs. GPT-5.5 Instant (0.186)
• SciCode: Claude Fable 5 (0.602) vs. GPT-5.5 Instant (0.486)
• LCR: Claude Fable 5 (0.7) vs. GPT-5.5 Instant (0.64)

Additionally, Claude Fable 5 provides data for IFBench (0.635), TerminalBench Hard (0.629), and TAU2 (0.985), demonstrating a broader range of evaluated capabilities.

Cost and Speed

Cost efficiency is a primary differentiator. GPT-5.5 Instant is priced at a blended rate of $11.25/1M tokens (Input: $5.00/1M, Output: $30.00/1M). Claude Fable 5 is more expensive, with a blended rate of $20.00/1M tokens (Input: $10.00/1M, Output: $50.00/1M). Performance metrics regarding output speed and time to first token remain unknown for both models.

Best Fit

GPT-5.5 Instant is best suited for high-volume tasks where cost management is critical and the workload does not require the absolute peak of current reasoning capabilities. Claude Fable 5 is the ideal choice for complex, multi-step reasoning, advanced coding tasks, and applications where accuracy and benchmark performance are the primary drivers of success.