Composer 2.5

Overview

Composer 2.5 is Cursor's in-house agentic coding model, released on May 18, 2026. It succeeded Composer 2 (March 19, 2026) and remains the current shipping model.

A successor is coming, but it does not exist yet. At its Compile conference in June 2026, Cursor announced "a new model — our first model trained from scratch." Cursor gave it no name, no version number, and no date, and as of July 8, 2026 it appears in neither the model list, the pricing table, nor the changelog. Treat the name "Composer 3" and the specifications quoted alongside it as press invention until Cursor says otherwise.

The single most important thing to understand about Composer, and the thing most coverage gets wrong, is stated plainly by Cursor itself:

"Composer 2.5 is built on the same open-source checkpoint as Composer 2, Moonshot's Kimi K2.5."

Composer is not a from-scratch Cursor model. It is a post-trained derivative of an open-source base — Moonshot AI's Kimi K2.5 — refined through continued training, reinforcement learning on long-horizon coding tasks, and synthetic task generation. Cursor's value-add is the post-training and the harness, not the pretraining.

That framing explains the model's economics. Cursor describes Composer 2 as "a new, optimal combination of intelligence and cost," and Composer 2.5 lands third on Artificial Analysis's Coding Agent Index at roughly 1/60th the per-task cost of the two models above it.

Cursor characterises Composer 2.5 as "a substantial improvement in intelligence and behavior over Composer 2" — "better at sustained work on long-running tasks, follows complex instructions more reliably, and is more pleasant to collaborate with."

Capabilities

• Long-horizon agentic execution — Cursor's documentation says the model "excels at long-horizon tasks via reinforcement learning on long-horizon coding tasks." Composer 2 was described as "able to solve challenging tasks requiring hundreds of actions."
• Tool use, file edits, and terminal operations — the model is "tuned for tool use, file edits, and terminal operations inside Cursor." It has access to all agent tools when used in Cursor.
• Sustained work — the specific improvement Cursor claims for 2.5 over 2: holding coherence across long-running tasks.
• Complex instruction following — Cursor cites more reliable adherence to multi-part instructions.
• Frontier-level coding — Cursor's own characterisation of Composer 2 was "frontier-level at coding."
• Low-latency variant — Composer 2.5 Fast is the default for interactive sessions, trading price for speed at the same intelligence tier.

Technical Specifications

• Base checkpoint: Moonshot AI's Kimi K2.5, open-source. Same base as Composer 2.
• Post-training: continued training and fine-tuning via reinforcement learning and synthetic task generation, applied by Cursor.
• Variants: Composer 2.5 (standard) and Composer 2.5 Fast (default for interactive sessions).
• Harness: full access to Cursor's agent tools — file editing, search, terminal.
• Weights: closed. Cursor's post-trained model is proprietary, even though its base is open.
• Availability: inside Cursor only. No standalone API.
• Context window: Not published by Cursor. Neither the launch post nor the model documentation states one.
• Maximum output tokens: Not published by Cursor.
• Architecture: Not disclosed beyond the base checkpoint identification. Cursor's Composer 2 announcement disclosed no architecture details.

The base-model disclosure matters for reasons beyond credit. Kimi K2.5's architecture, tokenizer, and pretraining data are Composer 2.5's architecture, tokenizer, and pretraining data. If you want to understand what Composer knows, read about Kimi K2.

Use Cases

• Long-running autonomous coding tasks — the workload Cursor explicitly reinforcement-trained for, spanning hundreds of sequential actions.
• In-editor agentic development — the model's native context, with full tool access inside Cursor.
• Terminal-driven work — Composer is tuned for terminal operations, and Terminal-Bench is one of the three benchmarks Cursor reports.
• Multilingual codebases — SWE-bench Multilingual is Cursor's third headline benchmark, at 73.7 for Composer 2.
• Cost-sensitive agent workloads — at $0.07 per task on Artificial Analysis's harness, Composer 2.5 makes high-volume agentic coding economically different from frontier alternatives.
• Interactive pair programming — the Fast variant exists for this, and is the default for interactive sessions.
• Mobile agent supervision — via Cursor's iOS app, in public beta since June 2026, which lets you "launch and manage always-on agents from anywhere."

Performance / Benchmarks

Cursor's own benchmarks (primary source)

From Cursor's Composer 2 announcement, comparing Composer 2 against Composer 1:

Cursor's Composer 2.5 launch post presents its benchmark tables and effort curves as charts rather than in text; the figures above are the ones Cursor states numerically.

Artificial Analysis (third-party evaluator)

Artificial Analysis independently evaluated Composer 2.5 on its Coding Agent Index. All figures below are Artificial Analysis's, not Cursor's.

Composer 2.5 ranks third, a 14-point gain over Composer 2's 48. Component movements from Composer 2 to Composer 2.5:

• SWE-Bench-Pro-Hard-AA: 12% → 47% (+35 points). Artificial Analysis notes this score is "comparable to Claude Opus 4.7 (max)."
• Terminal-Bench v2: 64% → 66% (+2 points)
• SWE-Atlas-QnA: 69% → 72% (+3 points)

Artificial Analysis also measured Composer 2.5 Fast at an average wall time of 6.7 minutes per task.

The headline is the cost column. Composer 2.5 sits 4 points behind the leading coding agent while costing roughly 1.7% as much per task.

Limitations

• Cursor-only. No standalone API, no weights, no third-party hosting. Using Composer means using Cursor.
• Not a from-scratch model. Composer inherits the capabilities, knowledge, and blind spots of Moonshot's Kimi K2.5. Cursor's post-training reshapes behaviour, not pretraining knowledge.
• No published context window. Neither the launch post nor the model docs state one, so long-context planning is guesswork.
• No published architecture or parameter count. Cursor discloses the base checkpoint and nothing further.
• Specialised for coding. Composer is tuned for tool use, file edits, and terminal operations inside Cursor. It is not a general-purpose assistant.
• Third place on the independent index. Artificial Analysis puts Composer 2.5 behind Claude Opus 4.7 and GPT-5.5 on raw capability. When the task justifies the cost, the frontier models still win.
• The Fast variant carries a real premium. At $3.00/$15.00 it is 6x the standard price, and it is the default for interactive sessions — worth knowing before your bill arrives.
• Knowledge cutoff not published. Recency of framework and library knowledge is unstated.

Pricing & Access

API pricing (per million tokens, from Cursor)

Cursor notes the Fast tier is "a lower cost than the fast tiers of other frontier models." Fast is the default for interactive sessions in Cursor.

Plan access

• Individual plans — Composer usage draws from the standalone usage pool.
• Team and enterprise plans — billed at direct API pricing.
• Cursor offered double usage for the first week after the Composer 2.5 launch.

Surfaces

• Cursor editor — the primary interface.
• Cursor for iOS — public beta on all paid plans since June 29, 2026. Launch and manage always-on agents remotely, with live activity tracking and artifact review.
• Cursor's new interface — Composer has been available in its early alpha since the Composer 2 release.

There is no way to access Composer 2.5 outside Cursor.

Ecosystem & Tools

• Cursor — the editor, and the only place Composer runs.
• Kimi K2 — Moonshot AI's open-source model line. Kimi K2.5 is Composer 2.5's base checkpoint; understanding K2 is understanding Composer's foundation.
• Cursor docs: Composer 2.5 — official model documentation.
• Cursor agent tools — file editing, semantic search, terminal execution. Composer has full access to all of them in Cursor.
• Cursor for iOS — mobile supervision of always-on agents, public beta since June 2026.
• Artificial Analysis Coding Agent Index — the leading independent evaluation of Composer 2.5.

Community & Resources

• Introducing Composer 2.5 — the official launch post, and the source of the Kimi K2.5 disclosure
• Introducing Composer 2 — the March 19, 2026 predecessor, with the CursorBench / Terminal-Bench / SWE-bench Multilingual table
• Composer 2.5 model documentation — official docs
• Cursor Composer 2.5 on the Coding Agent Index — Artificial Analysis's independent evaluation
• Cursor changelog — release history, including the iOS public beta
• Cursor pricing — current plan and usage pricing
• Cursor forum — community discussion and support