Anthropic's $965 billion Series H valuation, closed 28 May 2026 and overtaking OpenAI's $852 billion (31 Mar 2026), marks the consolidation of frontier enterprise AI into a hyperscaler-backed top two, which shifts the binding risk in a multi-year Claude or GPT contract from model capability to vendor pricing power and operational switching cost, making contractual exit terms rather than benchmark wins the procurement variable that matters.

Anchored on Anthropic's 28 May 2026 Series H announcement ($65B raised, $965B post-money, run-rate revenue crossed $47B, leads Altimeter/Dragoneer/Greenoaks/Sequoia, $15B hyperscaler tranche incl $5B Amazon, CFO Krishna Rao quote) and OpenAI's most recent round ($122B raised, $852B post-money, closed 31 Mar 2026). VERIFIED 2026-06-05: anthropic.com/news/series-h (primary, all Anthropic figures + Rao quote); OpenAI valuation via OpenAI's own accelerating-the-next-phase-ai post ($122B) and CNBC 31 Mar 2026 ($852B post-money) — OpenAI does not publish valuations on-site, so the comparison rests on contemporaneous financial press. Both figures are private-market marks, not public valuations; framed as such in the body. The claim is the market-structure read (consolidation to a hyperscaler-backed top two) and its procurement consequence (negotiate exit, not benchmark), NOT a prediction of either vendor's IPO outcome. 90-day cadence, market dynamics. Triggers: (1) a credible third frontier vendor or open-weight option taking material enterprise share; (2) enterprise AI prices falling rather than holding, indicating pricing power did not materialise; (3) a vendor offering structurally cheaper enterprise terms that re-open price as the deciding variable. Siblings: AM-191 (Big Four model concentration), AM-185 (frontier labs as systems integrators), the Karpathy-to-Anthropic vendor-trajectory read.