Anthropic’s September 22 announcement of Claude Opus 5.5, which explicitly stated that Sonnet 5.5 and Haiku 5.5 would follow in the coming weeks, is the main catalyst pushing market-implied odds toward a cluster of late-September and early-October dates. With Sonnet 5 still the current mid-tier model and no 5.5 identifier, pricing, or system card yet listed in official documentation as of September 23, traders see elevated near-term probability for an imminent drop while assigning meaningful weight to early October windows consistent with Anthropic’s historical cadence between flagship and mid-tier releases. The “on or prior to September 24” outcome at 46.5% reflects uncertainty around how quickly the lab can finalize and ship the follow-on model after the recent Opus update.