Same-day releases: Opus 5.5 beats Fable 5.1 on benchmarks, GPT-6 Luna cuts task cost 96%
kimmonismus · x · 2026-09-23
A recap of the same-day releases from Anthropic and OpenAI, with the verdict that there was no clear winner.
Anthropic
- Responded to feedback on how Opus communicates and gave subscribers a storable usage reset
- Opus 5.5 beats Fable 5.1 on every benchmark in its headline comparison table and reportedly costs 40% less than Opus 5 on typical workloads
- Sonnet 5.5 and Haiku 5.5 to follow in coming weeks
OpenAI
- Efficiency took center stage: GPT-6 Luna at max effort scores 66.6% on DeepSWE 1.1, comparable to Fable 5 at medium effort, at 96% lower cost per task; API pricing $0.10/M input, $0.50/M output
- GPT-6 Sol approaches Astra's factual reliability on internal evals and beats low-effort Astra on AutomationBench at xhigh effort
The author also flags unverified rumors of an OpenAI counterpart to Grok Bot. Core takeaway: capable models are getting dramatically cheaper.
Related event: Anthropic Launches Claude Opus 5.5: Stronger, 40% Cheaper, Tops AA Index(259 posts)→
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