--- title: OpenQASM 3 feature table description: A table of the language features included in OpenQASM 3. source: https://quantum.cloud.ibm.com/docs/en/guides/qasm-feature-table --- # OpenQASM 3 feature table Below is a list of the `OpenQASM 3` language features. For more details on these capabilities, see the [OpenQASM 3.X Live Specification](https://openqasm.com/). Key: - โŒ Not supported - ๐ŸŸก Partial support - โœ… Supported The meaning of the complete "supported" mark depends on the column: - *Qiskit SDK*: The feature can be parsed by [`qiskit.qasm3.loads`](/docs/api/qiskit/qasm3) (by using the `qiskit-qasm3-import` extension), represented in a [`QuantumCircuit`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit), and exported to OpenQASM 3 by [`qiskit.qasm3.dumps`](/docs/api/qiskit/qasm3#dumps). - *IBM Quantum Compute Service*: A circuit containing the corresponding Qiskit feature can be successfully executed on hardware through IBM Quantum Compute Service. The meaning of "partial support" typically depends on the linked notes. > **Note** > > The most common method of submitting circuits to IBM Quantum Compute Service is to create the circuit in the Python-space interface to Qiskit SDK. > Circuits constructed and submitted in this manner do not need to be loaded from OpenQASM 3 files into Qiskit SDK. > > If you do not use OpenQASM 3 directly yourself, you can safely use features that are supported for representation in Qiskit SDK, export to OpenQASM 3, and submission to IBM Quantum Compute Service. > This includes features that cannot be loaded by Qiskit SDK from OpenQASM 3. | OpenQASM 3 Feature | Qiskit SDK feature | Qiskit SDK | IBM Quantum Compute Service | Notes | | :----------------------------- | :----------------------------------- | :--------: | :-------------------------: | :--------------- | | comments | | โœ… | โœ… | [1](#1) | | QASM vstring | | โœ… | โœ… | [1](#1) | | `include` | | ๐ŸŸก | โŒ | [1](#1), [7](#7) | | unicode names | | โœ… | โœ… | | | `qubit` | `Qubit` and `QuantumRegister` | โœ… | ๐ŸŸก | [2](#2) | | `bit` | `Clbit` and `ClassicalRegister` | โœ… | โœ… | [3](#3) | | `bool` | `expr.Var` and classical expressions | ๐ŸŸก | โœ… | [4](#4) | | `int` | | โŒ | โœ… | [4](#4) | | `uint` | `expr.Var` and classical expressions | ๐ŸŸก | โœ… | [4](#4) | | `float` | `expr.Var` and classical expressions | ๐ŸŸก | ๐ŸŸก | [4](#4) | | `angle` | Implicit, as gate parameters | โŒ | ๐ŸŸก | [4](#4) | | `complex` | | โŒ | โŒ | [4](#4) | | `const` | | โŒ | โŒ | [4](#4) | | `pi`/`ฯ€`/`tau`/`ฯ„`/`euler`/`โ„‡` | Constant-folded into gate parameters | โœ… | โœ… | | | Aliasing: let | Quantum and classical registers | ๐ŸŸก | โŒ | [5](#5) | | register concatenation | Quantum and classical registers | ๐ŸŸก | โŒ | [5](#5) | | casting | `expr.Cast` classical expressions | ๐ŸŸก | ๐ŸŸก | [4](#4) | | `duration` | | โŒ | โŒ | | | `durationof` | | โŒ | โŒ | | | `ns`/`ยตs`/`us`/`ms`/`s`/`dt` | Durations of `delay` and `box` | โœ… | โœ… | [6](#6) | | `stretch` | `expr.Stretch` | ๐ŸŸก | ๐ŸŸก | [4](#4), [6](#6) | | `delay` | `Delay`/`QuantumCircuit.delay` | โœ… | โœ… | [6](#6) | | `barrier` | `Barrier`/`QuantumCircuit.barrier` | โœ… | โœ… | | | `box` | `BoxOp`/`QuantumCircuit.box` | โœ… | โŒ | [6](#6) | | Built-in `U` | `UGate`/`QuantumCircuit.u` | โœ… | โœ… | | | `gate` | | ๐ŸŸก | ๐ŸŸก | [7](#7) | | `gphase` | `QuantumCircuit.global_phase` | ๐ŸŸก | โŒ | [7](#7) | | `ctrl @`/ `negctrl @` | `AnnotatedOperation` | ๐ŸŸก | โŒ | [7](#7) | | `inv @` | `AnnotatedOperation` | ๐ŸŸก | โŒ | [7](#7) | | `pow(k) @` | `AnnotatedOperation` | ๐ŸŸก | โŒ | [7](#7) | | `reset` | `Reset`/`QuantumCircuit.reset` | โœ… | โœ… | | | `measure` | `Measure`/`QuantumCircuit.measure` | โœ… | โœ… | | | bit operations | | ๐ŸŸก | โœ… | [4](#4) | | boolean operations | | ๐ŸŸก | โœ… | [4](#4) | | arithmetic expressions | | ๐ŸŸก | ๐ŸŸก | [4](#4) | | comparisons | | ๐ŸŸก | โœ… | [4](#4) | | `if` | `QuantumCircuit.if_test` | โœ… | โœ… | [8](#8) | | `else` | `QuantumCircuit.if_test` | โœ… | โœ… | [8](#8) | | `else if` | `QuantumCircuit.if_test` | โœ… | โŒ | [8](#8) | | `for` loops | `QuantumCircuit.for_loop` | ๐ŸŸก | โŒ | [8](#8) | | `while` loops | `QuantumCircuit.while_loop` | โœ… | โŒ | [8](#8) | | `continue` | `QuantumCircuit.continue_loop` | ๐ŸŸก | โŒ | [8](#8) | | `break` | `QuantumCircuit.break_loop` | ๐ŸŸก | โŒ | [8](#8) | | `return` | | โŒ | โŒ | | | `extern` | | โŒ | โŒ | | | `def` subroutines (classical) | | โŒ | โŒ | | | `def` subroutines (quantum) | | โŒ | โŒ | | | `input` | `QuantumCircuit.add_input` | โœ… | ๐ŸŸก | [4](#4), [9](#9) | | `output` | | โŒ | โŒ | | ## Notes 1. These OpenQASM 3 program features have no impact on the execution and Qiskit strips them out as part of parsing the files. Files that use them can be submitted but they will have no effect. For `include` files, `stdgates.inc` is currently supported as input to Qiskit, and backend execution always requires circuits to have been compiled to the backend Instruction Set Architecture (ISA), where `include` files are irrelevant. 2) Qiskit SDK supports parsing and dumping OpenQASM 3 files with any `qubit` declarations. For execution on hardware, only circuits defined in terms of hardware qubits (for example, `$0`) are valid. Qiskit SDK automatically outputs OpenQASM 3 in terms of the supported hardware-qubit identifiers if the circuit was transpiled for a backend with layout information. 3. `bit`- and `bit[n]`-typed variable declarations in Qiskit SDK correspond to `Clbit` and `ClassicalRegister` declarations. 4) As of July 2025, Qiskit SDK can represent local variables of a restricted set of types, can represent many runtime operations on these objects, and supports outputting them to OpenQASM 3. However, Qiskit SDK (through `qiskit-qasm3-import` v0.6.0) does not support parsing OpenQASM 3 files that contain variable declarations, and has very limited support for parsing variable expressions. In general, most of what Qiskit can represent in its expression system can be executed on suitable dynamic circuits hardware, even if the expression cannot yet be parsed by Qiskit SDK. See [the Qiskit documentation of the `qiskit.circuit.classical` module](/docs/api/qiskit/circuit_classical) for the most up-to-date information. 5. Qiskit SDK can represent register aliasing for both quantum and classical registers, but it is strongly discouraged to use aliasing of classical registers. Most expressions on classical registers do not work with aliases, and aliased classical registers are not supported for execution on hardware. The Qiskit OpenQASM 3 parser can resolve `let` alias statements that bind the result of register concantenation. 6) Qiskit SDK supports explicit delays via `QuantumCircuit.delay`, and circuit boxes (`QuantumCircuit.box`) can also have explicit durations. These durations can include classical expressions of `stretch` variables. Qiskit SDK (as of July 2025 through `qiskit-qasm3-import` v0.6.0) does not support parsing declarations of type `duration` or type `stretch` from OpenQASM 3 files. Hardware has limited support for durations including `stretch`. 7. Circuits must be transpiled to the backend ISA to run on IBM hardware. This precludes custom `gate` definitions and higher-level constructs like gate modifiers (such as `inv @`) from being valid for execution on hardware verbatim, but the `transpile` process resolves them into valid ISA circuits. Qiskit SDK (as of July 2025, through `qiskit-qasm3-import` v0.6.0) will eagerly evaluate gate modifiers during the parse, so these will not be evident in the resulting `QuantumCircuit`, potentially at a runtime cost. 8) Qiskit SDK can represent structured control flow and export this to OpenQASM 3. The `continue` and `break` statements can technically be represented by Qiskit, but are not well supported even within Qiskit SDK. `for` loops in Qiskit v2.1.0 are not well supported. Nested control flow (such as an `if` inside another `if`, or an `else if` statement) is not eligible for execution on hardware. 9. Qiskit SDK supports declaring any supported classical type as an `input` variable on the circuit. Such variables are not currently eligible for execution on hardware, and cannot be loaded by the Qiskit OpenQASM 3 importer. Unbound `Parameter` objects present in the `QuantumCircuit` are exported as `input float[64]` variables. Certain runtime configuration options can enable executing such circuits on some backends. ## Next steps > **Recommendations** > > - Learn how to generate OpenQASM code using [IBM Quantum Composer](/docs/guides/composer). > - See the [OpenQASM 3 Qiskit API](/docs/api/qiskit/qasm3) reference. > - See the [OpenQASM 2 Qiskit API](/docs/api/qiskit/qasm2) reference. > - Review the [Verify your program](/docs/guides/debugging-tools) topic. > - Visit the [OpenQASM Live Specification](https://openqasm.com/).