Reason by Reason Machines

Not yet independently verified. Dated from the Y Combinator launch post of 13 November 2026; the maker's site gives no pricing or company location, and its cost, benchmark and user-count claims are the maker's own. We will update this when it can be confirmed, and remove this note.

Teams that pay for several AI coding tools often pay again for the harness that runs them. Reason, from Reason Machines, takes a different route: it is an agent harness that works on the customer's own API keys and subscriptions, so the spend goes to the model providers the customer already uses.

Sessions that move between machines

The launch post describes sessions running on cloud VMs that can follow the user across devices. Reason runs on cloud Linux, cloud Mac, local machines or SSH boxes, and handles hundreds of parallel sessions and long-running workflows. Keys and subscriptions are brought by the customer, with automatic failover between them.

An API, an app and Slack

The maker's site shows three ways in. Through the API, a prompt and a repository start a session that returns an ID, a status and a URL, which can be polled or streamed. In the app, users manage teammates and agents together and can run Claude Code, Codex and Cursor beside Reason. In Slack, mentioning @Reason in a thread brings back a pull request, a deck or an answer. Examples on the site include fixing a flaky test, porting code to Rust and building a reliability review deck from an incident log.

Cost and benchmark claims

The founders claim 30 to 80 percent lower cost per task than Codex, Cursor or Devin, and a score of 65.1 on the Coding Agent Index against 62.5 for Codex, at 22 percent lower cost per solved task. The site also says it is loved by more than 20,000 engineers. All of these figures are the maker's own and were not checked independently.

People and funding

Co-founders Adi and Sven both studied EECS at UC Berkeley. Adi worked in applied machine learning at Scale AI and earlier built a Rust-based IDE; Sven built AI models at a Fortune 100 company. YC companies are offered $1,000 in credits, and the company says it is raising a seed round.

Key facts

Maker: Reason Machines Founders: Adi and Sven Launched: Y Combinator launch post, 13 November 2026 Product: Reason, an agent harness for coding agents Pricing: not published; runs on the customer's own keys and subscriptions Backed by: Y Combinator