Release News: Qiskit v2.5 is here!

July 14, 2026 | Source: IBM Research

Tags: Qiskit, IBM, quantum computing, SDK release, transpiler, fault-tolerant quantum computing

IBM's Qiskit SDK v2.5 adds classical control flow inspection to its C API, a multi-representation compiler framework for fault-tolerant quantum computing (FTQC) pipelines, and significant transpiler speedups via LightSabre improvements and expanded multithreading.

Details

Qiskit v2.5 continues IBM's v2.x strategy of strengthening SDK foundations while opening up programmable performance controls. The headline additions: the C API now supports classical control flow inspection in dynamic circuits, closing one of the biggest remaining gaps between C and Python parity in Qiskit's core data model. A new multi-representation compiler framework introduces abstractions for building compilation pipelines that move between intermediate representations — critical for fault-tolerant quantum computing (FTQC) workflows that require staged lowering. New preset pass managers provide dedicated compilation pipelines for Pauli-based computation (PBC) and Clifford+T algorithm families. On the performance side, the transpiler receives "significant speedups" via LightSabre improvements, expanded multithreading, and a new fidelity-focused optimization pass — directly reducing circuit compilation time for real hardware execution. IBM also renamed Qiskit Runtime Service to IBM Quantum Compute Service, explicitly clarifying the split between the open-source Qiskit SDK and IBM's commercial quantum offerings. No API or workflow changes accompany the rename. For developers working on quantum circuits today, the C API expansion and transpiler speedups are immediately practical. The multi-representation compiler framework is more forward-looking — it targets the compilation complexity that FTQC will require at scale.