Opus 5 and the 1M Promise: does Claude stay good over its whole context window?
Anthropic’s prompting guide for Opus 5 says: “Claude Opus 5 has a 1M token context window as both the default and the maximum, and its instruction following, tool calling, and reasoning stay consistent throughout the window.” No number backs the second half. So I checked it. Context Arena, an independent site, runs a test called […]
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