The 2026 enterprise agentic AI vendor comparison reduces to four credible platform plays (Anthropic, OpenAI, Google, Microsoft), and the procurement decision between them is no longer primarily about model capability. The model layer has converged to comparable parity for most enterprise use cases. The procurement decision in 2026 is on three other axes: pricing model (Anthropic Managed Agents at 8 cents per session-hour plus tokens versus OpenAI Agents SDK at no first-party runtime fee versus Microsoft and Google's vertically-integrated platform pricing), governance and BAA posture (Anthropic's three-cloud BAA position is structurally distinct), and ecosystem distribution (Microsoft's Office plus Azure footprint has no near peer; Google's vertical integration on Workspace and Cloud is second). Treating this as a model-quality bake-off is the most common 2026 procurement mistake and produces decisions that age badly within the first 12 months.

Claim is scoped to enterprise procurement of agentic AI platforms in 2026. The four credible plays are based on observed market share, enterprise reference customers, and platform completeness. Smaller specialised vendors (Cohere, Mistral, others) compete on specific verticals or use cases but do not currently meet the platform-completeness bar for general enterprise agentic AI procurement. 60-day review cadence. Watches: (1) major repricing or model-tier changes at any of the four vendors, (2) regulatory enforcement actions that materially affect one vendor's enterprise-suitability profile, (3) entry of a credible fifth platform (most plausibly via the Linux Foundation Agentic AI Foundation member firms or via a major systems-integrator-backed neutral platform).