Address #2543

docs/migration-guides/_toc.json

@@ -54,6 +54,10 @@
             "title": "Migrate from qiskit-ibm-provider",
             "url": "/migration-guides/qiskit-runtime-from-ibm-provider"
           },
+          {
+            "title": "Migrate from a third-party provider",
+            "url": "/migration-guides/qiskit-runtime-from-third-party-provider"
+          },
           {
             "title": "Migrate options",
             "url": "/migration-guides/qiskit-runtime-options"

docs/migration-guides/qiskit-runtime-from-third-party-provider.mdx

@@ -0,0 +1,61 @@
+---
+title: Migrate from a third-party provider
+description: Migrate from a third-party provider to using Qiskit Runtime primitives
+
+---
+
+# Migrate from a third-party provider
+
+This topic shows how to migrate code from a third-party provider that implemented `IBMBackend.run()` to use `qiskit_ibm_runtime`.
+
+The Qiskit SDK offers wrappers for `backend.run` that can be easily adapted to a custom primitives workflow
+through subclassing; these are the [`BackendEstimatorV2`](/api/qiskit/qiskit.primitives.BackendEstimatorV2) and [`BackendSamplerV2`.](/api/qiskit/qiskit.primitives.BackendSamplerV2) The inputs
+to the primitives should follow the Primitive Unified Bloc (PUB) syntax specified in the V2 primitives interface. See the [Overview of PUBs section](/guides/primitive-input-output#pubs) in the Primitive inputs and outputs guide for details.
+
+An advantage of this strategy is that the wrapper can handle the input and output manipulation, so knowledge of the PUB data
+model is not required. However, this might result in a suboptimal runtime, which could be refined through a fully
+custom primitives implementation.
+
+The following snippets show how to create a custom Estimator instance following the strategy described above.
+The process is analogous for a custom Sampler, modifying the base class to `BackendSamplerV2`.
+
+``` python
+from qiskit.primitives import BackendEstimatorV2
+
+class CustomEstimator(BackendEstimatorV2):
+    """Estimator primitive for custom provider."""
+
+    # This line is for type checking purposes.
+    # We are changing the type of self._backend from qiskit's
+    # BackendV1/BackendV2 classes to our custom provider resource.
+    _backend: CustomProviderResource
+
+    def __init__(
+        self,
+        backend: CustomProviderResource,
+        options: dict | None = None,
+        extra_flag_used_in_estimation: bool = True,
+        another_extra_flag: bool = False,
+    ) -> None:
+        """
+        Args:
+            backend: custom provider resource to evaluate circuits on.
+            options: options passed to through to the underlying BackendEstimatorV2.
+            extra_flag_used_in_estimation:  if `False`, do this.
+            another_extra_flag: if `True`, do that,
+        """
+
+        # preprocess arguments if necessary according to custom flags
+        processed_backend = ...
+        processed_options = ...
+
+        super().__init__(
+            processed_backend,
+            options=processed_options,
+        )
+
+    @property
+    def backend(self) -> CustomProviderResource:
+        """Computing resource used for circuit evaluation."""
+        return self._backend
+```

qiskit_bot.yaml

@@ -278,6 +278,10 @@ notifications:
     - "@jyu00"
     - "@ElePT"
     - "@beckykd"
+  "docs/migration-guides/qiskit-runtime-from-third-party-provider":
+    - "@jyu00"
+    - "@ElePT"
+    - "@beckykd"
   "docs/migration-guides/qiskit-runtime-from-ibmq-provider":
     - "@jyu00"
     - "@ElePT"