Anthropic’s release of Claude Sonnet 5.5 on September 28, just days after Opus 5.5, underscores the company’s accelerated cadence in the 5.x series and directly shapes trader views on when a 5.6+ Sonnet will arrive. Sonnet 5, launched June 30, emphasized agentic tool use, coding, and reasoning at lower cost than Opus 4.8; the 5.5 update adds 30% faster inference and reduced token usage for routine tasks while maintaining the same $2/$10 pricing tier. This rapid iteration, typical of 21-day intervals across recent Anthropic drops, points to ongoing pressure from competitors and internal roadmaps favoring frequent, incremental gains in benchmarks like SWE-Bench and agent evaluations rather than longer waits for major jumps. Traders are watching for any October announcements or developer conferences that could accelerate or delay the next Sonnet threshold.